Tests for HIV infection: features of the procedure and interpretation of the results. In what cases and when is HIV ELISA performed? Testing for HIV using the IFA method

The human immunodeficiency virus is a dangerous disease that, despite the efforts of medical specialists, is spreading at a high rate. Much attention is paid to the fight against this disease throughout the world. But a miracle vaccine against AIDS has not yet been found. In modern medicine, there are several methods for diagnosing the immunodeficiency virus, but the most common among them is enzyme immunoassay. HIV ELISA began to be used several decades ago. All these years, this diagnostic method has been improved. And today it is also considered one of the most accurate. The reliability of the ELISA test for HIV is high. It is ninety-six to ninety-eight percent. The margin of error for a false positive or false negative result is small. Thanks to this, the popularity of such diagnostics becomes clear. How is HIV detected by ELISA, where can this test be taken and how to prepare for it?

Description of the HIV ELISA test

An ELISA test for HIV is aimed at detecting antibodies to this disease in a person’s blood. Once this virus enters the human body, it does not immediately begin its active activity. Accordingly, up to a certain point it may be impossible to identify it. Medical experts recommend testing for the immunodeficiency virus no earlier than several weeks after suspected infection.

ELISA detects antibodies to HIV with a high degree of probability. It is worth noting that this test can detect antibodies in blood serum. It determines not only their presence. HIV blood ELISA also helps to identify the total spectrum of antibodies. To some extent, such information helps determine the time at which infection occurred to within a week. This is necessary not only so that an infected person can guess under what circumstances the infection occurred. The number of antibodies to HIV in ELISA is information that is also needed by medical specialists. With its help, they can subsequently monitor the patient’s condition, determining with great accuracy how the virus will behave in the coming weeks or months. A patient who has already been diagnosed can be offered to donate blood using the ELISA test for HIV. This procedure is necessary in order to determine the quantitative composition of antibodies and prescribe the correct antiretroviral therapy regimen.

In modern medicine, in particular in our country, 4th generation ELISA is used today for HIV. This analysis has been refined over the years, and today its reliability is ninety-six to ninety-eight percent. The error is small, but it is there. Therefore, to be on the safe side, patients with a diagnosis established by enzyme immunoassay are also tested using immunoblotting. In other words, 4th generation ELISA test systems for HIV make it more likely to identify people without a diagnosis of the immunodeficiency virus. In this case, a re-check is not carried out. If the enzyme immunoassay shows the presence of antibodies to the immunodeficiency virus, patients are referred for other types of tests.

How is HIV testing performed using ELISA?

An ELISA blood test for AIDS is taken from a vein. As with other known methods of research for identifying the immunodeficiency virus, blood serum is used as a biological material for enzyme immunoassay testing. The patient comes for analysis on an empty stomach. There are no special restrictions in terms of food intake and abstinence from alcohol in this regard. However, excessive consumption of alcoholic beverages before the test may negatively affect the results. Everyone should know about this.

Antibodies to HIV are detected by ELISA in several stages. In addition to the patient’s biological material, in this case it is venous blood, such a procedure requires artificial serum with immunodeficiency virus protein and a solid base. The latter uses a special tablet, which can be made of polystyrene or other moderately porous materials. The study of blood samples in ELISA for HIV/AIDS begins by combining the patient's blood with the protein that contains the virus. After this, the laboratory assistant observes the reaction between the patient’s blood serum and the disease cells. The test material is washed several times with special enzymes. If the reaction is persistent and the production of antibodies begins, it means that the patient’s body has an immunodeficiency virus. However, doctors do not draw final conclusions based on enzyme immunoassay for HIV. For this purpose, additional diagnostic methods are used.

It is worth noting that the 3rd generation HIV ELISA is still used today. It differs slightly from fourth-generation test systems by more effective enzymes. But this analysis is less expensive, so it is most often used in public clinics.

HIV ELISA test: timing of testing

Specialized HIV ELISA diagnostic laboratories are now available in all major cities. Large laboratories specializing in various tests also carry out testing using enzyme immunoassay testing. It is worth noting that today people living in small towns have the opportunity to take an ELISA test for HIV, in a month (the reliability of the result largely depends on the period of testing) or more time after the suspected infection. And for this they do not have to come to regional centers. Tests for the immunodeficiency virus are carried out in all clinics and even in some rural and town outpatient clinics. However, employees of small medical institutions subsequently send blood serum samples to specialized laboratories. An ELISA test for HIV in both cases will not differ in results. The only disadvantage of “start” tests is that their readiness time is longer. In other words, residents of megacities will learn the results of the test the next day or even on the same day. Those who get tested in small towns sometimes wait from one to several weeks for ELISA results.

HIV ELISA in a month, two or several weeks: when to get tested?

The main mistake people make when wanting to be tested for the presence of the immunodeficiency virus in their blood is that they get tested too early after the suspected infection. Medical experts recommend this type of check be carried out at least three weeks later. Will ELISA for HIV always show results in 4-6 weeks or not? This question is often asked to medical professionals. No one has the right to answer in the affirmative and declare that ELISA for HIV in 5 weeks, 6 or a month will show one hundred percent. It all depends on the individual characteristics of the body. The fact is that once the virus cells enter the blood or other environment, they do not immediately take active action. It takes them a certain time to begin multiplying inside the human body, as well as to begin destroying leukocytes. ELISA for HIV infection during a period when virus cells have not spread in the blood in sufficient quantities is ineffective. That is why it is pointless to conduct such an analysis a day or even a week after the alleged infection. This period is called the seronegative window by medical experts. It is worth noting one of its characteristic features. It is impossible to determine the presence of the immunodeficiency virus in the body during this period. But a person whose disease is still undetected is already potentially dangerous to others because he can spread the virus.

An ELISA blood test for HIV will reveal the presence of this disease in 3-4 months. In some cases, it is during this period that a person first learns about a terrible diagnosis. It depends on some characteristics of the body. Whether IFA will determine HIV after 2 months, a month or several weeks is largely influenced by the concentration of the virus that entered the body. If we are talking about blood transfusion or unprotected contact, then its concentration will obviously be high. Therefore, using ELISA it will be possible to determine HIV antibodies not in 5 months, but much earlier. In rare cases, people may find out about a terrible diagnosis much later. There have been cases when the HIV ELISA showed a positive result only after a year. This could be determined by the concentration of virus cells. Fortunately, such cases are very rare. They make up only 0.5% of all infected people.

Where can I get an ELISA test for HIV 1, 2?

The question of where to take an ELISA test for HIV 3 or 8-10 weeks after the alleged infection is of interest to many. In our country, this can be done in a clinic at your place of residence or temporary residence. The procedure is free. In order to take an HIV ELISA test after 12 weeks or earlier, you do not need to take a referral from a general practitioner or virologist. You should inform the receptionist if you wish to be tested for this disease. You should have your passport and compulsory health insurance with you. By the way, recently, you can undergo verification anonymously. Such testing for the immunodeficiency virus is also free. The patient is assigned an individual number by which he can find out the results after they are ready.

Why should I even get tested for HIV?

HIV testing is the only way to determine whether you have HIV or not. When you know your HIV status, you are confident in your health and know that you will not infect your loved one. The earlier HIV is detected, the sooner you can start treatment and maintain your health.

Be sure to get tested for HIV if:

you had intercourse without barrier protection,
Have you used a used needle, syringe,
You had a risky contact and it worries you very much. It’s better to get checked once than to suffer for a long time from the fear of the unknown.

Many people are afraid to take an HIV test, but in vain. It is better to get tested and know about your HIV status than to worry in vain (if HIV minus) or infect others (HIV plus).

Why shouldn't you be afraid to get tested for HIV?

It's very easy and fast. Testing for HIV can be done quickly and easily using a rapid saliva or blood test.
Better to know. It's normal to be afraid to test for HIV. But you need to overcome yourself and put an end to it; it is much better to either forget about it (provided that risky behavior is excluded) or begin treatment immediately if the result is positive.
Will help you live a long and happy life. If you are diagnosed with HIV in the early stages, then your life is not over, but on the contrary, it is just beginning + you can start therapy early and avoid AIDS. With proper treatment and care, a person infected with HIV can live a quality life like the average HIV-negative person.
Treatment is free. If you are diagnosed with HIV, you will receive free expensive medications that will lower and strengthen the immune system.
Healthy sex life. If you know your status and the HIV result of your partner, then you will be calm about your sexual intercourse. You won't infect each other with anything.

May the hand of the giver never fail

Project "AIDS.HIV.STD." is a non-profit, created by volunteer HIV/AIDS experts at their own expense to bring the truth to people and to be clear before their professional conscience. We will be grateful for any help to the project. May it be rewarded to you a thousandfold: DONATE .

A Brief History of HIV/AIDS Testing

1981 - first case of AIDS.

1984 - detection of HIV.

1985 - The first HIV test was certified.

1987 - the first Western Blot test system was created.

1992 - the first rapid test was introduced.

1994 - the first test for detecting HIV in saliva was created.

1996 - the first home test and urine test to detect HIV.

2002 - the first rapid finger test for HIV.

2004 - the first rapid test for detecting HIV in saliva.

When should you get tested for HIV?

You can be tested for HIV at any time, especially when you have had contact with an HIV-positive person or you do not know whether he/she has HIV infection or not.

Even if you think that you have no risk of contracting HIV, get tested at least once a year. This will not interfere at all and you yourself will be calm and confident.

What is the correct name for a blood test for HIV?

ELISA, Immunoblot, PCR.

I was at risk of contracting HIV, when should I get tested?

If you have had unprotected intercourse or have used a used syringe or needle (even if it is “sterilized”), then do not hesitate and consult a doctor as soon as possible to determine the risk of HIV infection and prescribe tests, etc.

2 weeks have passed since contact with an HIV-infected person

A month has passed since high-risk contact with a person who may have HIV

The ELISA method using 4th generation test systems is suitable.

If you are sure that you have become infected (which is usually 99% untrue), remember that a person infected with HIV is most contagious and poses a danger to his contacts. in the early stages of HIV infection. Therefore, follow safety measures: either abstain from intercourse, psychoactive substances or.

How long after can I take my last HIV test to be 100% sure that I have not contracted HIV?

Take the last HIV test, forget and continue to think with your head:

ELISA 4th generation - 6 weeks on the perceived risk;
HIV RNA PCR - 4 weeks from the expected risk;
ELISA 3rd generation - 12 weeks from the expected risk.

What generation was my HIV test?

For the Russian Federation - usually the fourth (for Belarus, Ukraine - the 3rd). The name of the 4th generation test usually contains one of the words: “Combo”, “At/Ag”, “AT/AG”, “antigen-antibody” or “p24”. In any case, so as not to guess - Find out for sure from your healthcare professional. You are required to provide this information.

I think I was NOT at risk of contracting HIV, should I be tested for HIV?

At least 2 times a year you need to be examined for HIV and other sexually transmitted diseases in order to notice the disease in time and treat it, and to be sure - it’s calmer.

I'm pregnant, do I need to be tested for HIV?

Necessarily! Most likely, you will be offered an HIV test at the antenatal clinic or maternity hospital. Don't refuse! This is important for your child's health. If the doctor knows that you are HIV positive, he will be able to help protect your child from HIV infection.

Is it possible to find out if you have HIV infection without tests?

It is possible with a high degree of probability to be diagnosed with HIV infection, but ONLY in the AIDS stage. Before AIDS, you can also SUSPECT HIV infection. Before the stage of secondary manifestations, AIDS, especially in the latent stage, an HIV-infected person will look like an ordinary person !

How do diagnostic test systems for determining HIV and AIDS work?

3rd generation tests (ELISA antibody)

When a person becomes infected with HIV, his body produces antibodies (defenders, special proteins that attack the virus). Antibody ELISA test detects these antibodies in blood, saliva and urine. If it finds antibodies, it means the person is infected with HIV. This test is only accurate 3 months after infection, because... it takes time for the body to produce the required level of antibodies that the test can detect.

What are antibodies?

Antibodies- These are immunoglobulin proteins that bind to bacteria and viruses and neutralize them. Each antibody is specific, i.e. it binds and neutralizes only one type of bacteria or virus and has no effect on others. Antibodies in humans are produced by blood cells - B-leukocytes.

Antibody is a protein (immunoglobulin) that circulates in the blood plasma and binds to the antigen that caused its formation.

What are antigens?

Antigen- any substance (usually protein, but can also be carbohydrate) that causes the production of antibodies by lymphocytes. Proteins and other substances on the surface of any “non-self” cells are considered antigens and cause a similar specific response, i.e. antibody production.

In the case of HIV antigens are virus proteins.

4th generation tests (Combined antigen-antibody ELISA)

4th generation tests also detect antibodies (proteins of the human immune system that are produced in response to infection), but also the p24 antigen, and therefore determine the presence of HIV earlier than 3rd generation ELISA tests.

Antibodies are produced by the body in response to HIV infection, but their production takes some time (“window period”).

p24 antigens are particles of the HIV virus itself; there are a lot of them in the blood in the first few weeks after HIV infection; it is during these first few weeks that an HIV-infected person is most contagious.

The HIV p24 antigen, which is usually determined by test systems, is the protein of the viral capsid (core component), the essence is a piece of the virus itself, it is clear that it begins to be detected in the blood earlier than antibodies. Those. The “window period” for the 4th generation test is very small.

When antibodies against HIV begin to be detected in large quantities, after some time, the p24 antigen is often no longer detected, because a complex is formed between the antigen and antibodies in the blood, the protein becomes associated with another protein.

4th generation tests can detect the HIV virus 11 days to 1 month after infection. Proof:

“The detection of acute HIV infection” J Infect Dis. 2010 Oct 15;202 Suppl 2:S270-7. Cohen MS, Gay CL, Busch MP, Hecht FM. — 17 days;
“How can we better identify early HIV infections?” Rosenberg NE, Pilcher CD, Busch MP, Cohen MS. — 5-10 days after detection by PCR method is possible (7-10 days);
“Diagnosing acute HIV infection” Expert Rev Anti Infect Ther. 2012 Jan;10(1):31-41. Yerly S, Hirschel B. - 20-25 days for 3rd generation systems, and 4 days less for 4th generation systems (median value, range 2-14 days).

Laboratory ELISA systems of the 4th generation with a very high probability “will not miss” HIV infection within a month from the field of infection.

Quick (express) tests

With the help of rapid tests, the result for HIV can be obtained anywhere on the spot, even at home, BUT... the probability of a false positive result when using rapid tests is much higher, p.e. anyway, then you need to redo it on normal ones.

Rapid test kits for determining HIV infection.

Self-test

In order to determine the presence of HIV at home, you need to buy a rapid HIV test at the pharmacy. Usually, the pharmacy sells tests for detecting HIV by saliva, which are very convenient. Follow the instructions for using the test exactly. If the result is positive, contact immediately.

How to get tested for HIV?

There are several facilities where you can get tested for HIV. Analysis can be done in the clinic at the place of residence. To do this, you need to contact your local therapist. The analysis is carried out using the method ELISA (enzyme-linked immunosorbent assay). Result usually ready within 7 – 14 days.

You can get tested for HIV at the AIDS Prevention Center, if there is one in your city. Here you can donate blood anonymously without providing your personal information. The result will be ready in the period from 2 to 7 days(possibly the very next day).

HIV testing is carried out in these institutions for free. In private medical centers You can get tested for HIV for a fee. The advantage here is that the analysis is ready within a few hours to the first day.

It is even possible to conduct research at home using rapid tests, which are now sold in pharmacies throughout the Russian Federation.From the point of view of common sense, this is not the best option, since if you receive a negative result, you cannot be 100% sure that you do not have HIV, and if it is positive, you will need to retest it using another method (ELISA), since there is a possibility of obtaining a false positive result.

New algorithm for detecting HIV.

What are false positive and false negative results in HIV testing?

False positive result

False positive result (when there is no infection in the body and the test result is positive) can be obtained for a number of reasons. Some so-called autoimmune diseases (rheumatoid arthritis, systemic lupus erythematosus, scleroderma, etc.), allergic diseases in the active phase, pregnancy, hormonal disorders, acute infectious diseases, oncological diseases, sharply elevated levels of blood components (cholesterol), recent vaccinations can lead to the appearance of antigens in human blood, which, due to high sensitivity, can be “caught” by the test system. In addition, errors by medical personnel can simply lead to a false result, "human factor":

the tubes were labeled incorrectly,
made a mistake when introducing the sample during analysis,
documentation errors
mixed up the test tubes
they gave the wrong result,
contaminated the sample, etc.

False negative result

False negative result (HIV – there is an infection, but the test result is negative). One of the common reasons for obtaining such a result is the “” period. Another reason - immune system failure a person either in the final stage of the disease - the AIDS stage, or when taking immunosuppressive therapy - after organ transplantation, as well as in immunodeficiencies. In this case, the person’s immune system is simply unable to produce antibodies to HIV, which are detected during testing. Factors of a technical nature cannot be excluded - errors in the storage and transportation of blood donated for testing, during the analysis.

What are antibodies to HIV?

What is the serological window (seroconversion) period?

This is the period of time after a person is infected with HIV, when the virus is present in the blood, often in very large quantities, and the immune system has not yet developed antibodies to the virus. In such people, the result of an HIV test using ELISA will be negative, since this method detects antibodies to HIV in the blood. Typically, antibodies in the majority of infected people appear in the blood within three months after infection, in a small percentage of people - after 6 months, in a few - up to a year.

What is tested for HIV?

To test for HIV using ELISA, blood is taken from a vein. When using express tests, it is possible to use blood from a finger, saliva and urine.

How to prepare for an HIV test?

You need to take an HIV test on an empty stomach, since some substances that enter the blood after eating can affect the accuracy of the test system. So, if cholesterol and lipids in the blood rise sharply after eating fatty foods, this can lead to distorted results.

What are the best methods to do a blood test for HIV?

During the patient’s initial visit, the blood is tested using ELISA. Its advantages are very high specificity (that is, antibodies are detected only to the human immunodeficiency virus and to no others) and sensitivity (even the smallest concentrations of antibodies to HIV are determined).

There are so-called rapid tests for rapid analysis of HIV. They are based on the immunochromatography method. To diagnose HIV infection using this method, you can use whole blood from a finger prick and saliva. But the reliability of these rapid tests is lower than ELISA.

False Positive Rate results when using them reaches 1%. According to the sanitary rules “On the Prevention of HIV Infection,” testing for antibodies to HIV using rapid tests must be accompanied by mandatory testing of the same portion of blood using standard laboratory technologies approved for use in the Russian Federation.

It is possible to diagnose HIV infection using the method, but it is not recommended, because very expensive, longer and technically more complex than ELISA, which implies a greater risk of errors. Testing of a patient at his first visit is always carried out using the ELISA method, since it is simpler to perform, does not require much time and special conditions (PCR - laboratories), but is quite reliable. However, the use PCR allows you to diagnose infection during the serological window, starting from 10–14 days of infection. It should also be taken into account that the sensitivity of PCR reaches 98%, which is lower than that of ELISA (more than 99.5%). In addition, PCR analysis is paid and not cheap. The optimal diagnostic option is the ELISA method using 4th generation test systems that detect both antibodies to HIV and p24 antigen. This allows you to obtain a reliable result during the period of seroconversion.

Why are HIV test results delayed?

The issuance of an HIV result is delayed if a positive HIV test result is obtained. The fact is that there is a certain algorithm for diagnosing HIV infection. If a positive result is obtained, the same portion of blood should be tested in another test system from a different manufacturer or test format. If a repeated positive result is obtained, the sample is tested in a test system, again from a different manufacturer or a different format. Upon receipt of the third “plus” result, the blood is sent for research in the immune blotting reaction.

What is an immunoblotting test?

This is a type of ELISA that detects not antibodies to all components of HIV, but antibodies to specific proteins of the virus. The bottom line is that the virus contains various proteins: shells, cores and enzyme proteins. On the strip (a strip similar to a pregnancy test), these proteins are applied in the form of stripes. When exposed to serum from an infected person, a series of reactions results in these bands becoming visible. If the serum does not contain antibodies to HIV, the strip remains clean. This method is a reference method, that is, based on its results in conjunction with clinical manifestations and epidemiological data (in the presence of risks of infection, unprotected contacts, use of injecting drugs, etc.), a diagnosis of “HIV infection” is made.

Why is it recommended to donate blood again after 2-3 months after receiving a negative result for HIV?

To exclude blood donation during the serological window. It should be noted that currently, for ELISA diagnostics, a 4th generation test system is used, which detects not only antibodies to HIV, but also the p 24 antigen, which appears in the blood from the end of the second week of the disease and is an indicator of HIV multiplication in the blood. This reduces the likelihood of getting a false negative result.

Graph of the dynamics of the appearance of HIV markers.

When HIV markers appear, the “window period.”

How to interpret the result of an HIV test?

Negative for HIV

If you donated blood for HIV using the ELISA method, the result will be "negative" means what you have no antibodies to HIV detected. This indicates either that you not infected with human immunodeficiency virus, or that antibodies in the blood after meeting him did not have time to be developed by the immune system.

What to do in this case to eliminate all doubts?

Donate blood using the same method in two to three months, which will practically eliminate infection if a negative result is obtained. If you are an anxious person, then the third repeat of the test after another six months means that you do not have HIV in your blood (if, of course, there are no risks of infection during this time interval).

Positive for HIV

Upon receipt positive result or formulation “antibodies to HIV detected” , it is necessary not to stop at this stage and be sure to continue the examination for several reasons.

Firstly, there is a possibility of obtaining a false positive result. You may have a chronic illness, pregnancy, or other factors that may affect the blood testing process. To avoid errors in diagnosis, there is an algorithm for studying primary positive blood, which consists of several stages.
Secondly, if you are truly infected with HIV, then your quality of life directly depends on the timely start of antiviral therapy. It has already been proven that when treatment begins in the stage of acute HIV infection, the life expectancy of an HIV-infected patient approaches the average life expectancy of a healthy person.

When I was diagnosed with HIV infection many years ago, I thought that now it would dominate my whole life. But today, for me, HIV is a tiny virus that I control, not it controls me.
- Alexei.

I took a quick test in a mobile anonymous testing room and never expected that the test would show me a positive result. I howled like a wounded beluga: “Who will raise my children??!!! How long do I have to live??” But I was lucky, I came across a very cool doctor, and he told me that he knows a bunch of people who live with HIV for 20 years and feel fine and even give birth to several children, and this helped me survive this stress. I literally lived by his words for the first few hardest months. And now everything is fine with me, I have wonderful children, family, work!
- Sasha.

Remember! Now HIV infection is being treated, life is not over, but a new, rethought life is beginning, and HIV is not a death sentence, provided that it is treated correctly and regularly with antiretroviral therapy. Be sure to regularly visit the doctor at the AIDS center, give him the opportunity to do his job and help you. Don’t give in, these are poor, unhappy people who find themselves in a deep hole and are dragging others there.

Also, at the same time, you can check for sexually transmitted diseases: syphilis, trichomoniasis, gardnerellosis.

Where can you get help in this situation?

If you donated blood at a clinic, you will be referred to an infectious disease specialist. If the analysis was done anonymously in a private center or at home using rapid tests, you can contact either the AIDS Prevention Center or an infectious disease specialist at a local clinic. And remember Your life is in your hands!

Who must have their blood taken for HIV?

Patients with drug addiction (code 102 will be indicated in the referral for HIV),
For those who have received blood transfusion, blood components (plasma, red blood cells) (code 110),
Donors of blood, plasma, (code 108),
Sick (code 104),
Homosexuals, (code 103),
Children born from HIV-infected mothers (code 124),
Prisoners, (code 112),
Contacts through heterosexual sexual intercourse (code 121), drug transmission with HIV+ (code 123),
Pilots, flight attendants and air traffic controllers, (code 118),
Railway workers (drivers, switchmen, those who maintain tracks and trains), (code 118),
Conscripts, military, (code 111),
Police, (code 118),
Medical workers, doctors, (code 115)
Foreigners, (code 200),
Pregnant women, (code 109),
For clinical indications with symptoms similar to AIDS (code 113),
Patients with hepatitis B, C (code 118),
Deceased with suspected HIV (drug addicts, homeless people, etc.), (code 118),
indigenous small peoples of the North (Nenets, Khanty, Mansi, Komi, Zyryans, etc.), (code 118).

In recent years, there has been significant progress in identifying this terrible disease: older test systems are being replaced by more advanced ones, examination methods are becoming more accessible, and their accuracy is significantly increasing.

In this article we will talk about modern methods for diagnosing HIV infection, knowledge of which is useful for timely treatment of this problem and maintaining a normal quality of life for the patient.

HIV diagnostic methods

In Russia, a standard procedure is carried out to diagnose HIV infection, which includes two levels:

Other methods can also be used for diagnosis:

ELISA test systems

At the first stage of diagnosis, a screening test (ELISA) is used to detect HIV infection, which is based on HIV proteins created in laboratories that capture specific antibodies produced in the body in response to infection. After their interaction with the reagents (enzymes) of the test system, the color of the indicator changes. Next, these color changes are processed using special equipment, which determines the result of the analysis performed.

Such ELISA tests can show results within a few weeks after the introduction of HIV infection. This test does not determine the presence of the virus, but detects the production of antibodies to it. Sometimes, in the human body, the production of antibodies to HIV begins after 2 weeks after infection, but in most people they are produced at a later date, after 3-6 weeks.

There are four generations of ELISA tests with varying sensitivities. In recent years, third and fourth generation test systems have been increasingly used, which are based on synthetic peptides or recombinant proteins and have greater specificity and accuracy. They can be used to diagnose HIV infection, monitor HIV prevalence, and ensure safety when testing donated blood. The accuracy of generation III and IV ELISA test systems is 93-99% (tests produced in Western Europe are more sensitive - 99%).

To perform an ELISA test, 5 ml of blood is taken from the patient’s vein. At least 8 hours must pass between the last meal and the analysis (usually it is performed in the morning on an empty stomach). It is recommended to take such a test no earlier than 3 weeks after the suspected infection (for example, after unprotected sexual intercourse with a new sexual partner).

ELISA test results are obtained in 2-10 days:

negative result: indicates absence of HIV infection and does not require contacting a specialist;
false negative result: can be observed in the early stages of infection (up to 3 weeks), in the later stages of AIDS with severe suppression of the immune system and with improper blood preparation;
false positive result: can be observed in some diseases and in case of improper blood preparation;
positive result: indicates HIV infection, requires carrying out an IB and the patient contacting a specialist at the AIDS center.

Why can an ELISA test give false positive results?

False-positive HIV ELISA test results can occur due to improper blood processing or in patients with the following conditions and diseases:

multiple myeloma;
alcoholic hepatitis;
infectious diseases caused by the Epstein-Barr virus;
condition after dialysis;
autoimmune diseases;
against the background of pregnancy;
condition after vaccination.

For the reasons described above, nonspecific cross-reacting antibodies may be present in the blood, the production of which was not provoked by HIV infection.

In recent years, the frequency of false-positive results has decreased significantly due to the use of generation III and IV test systems, which contain more sensitive peptide and recombinant proteins (they are synthesized using genetic engineering in vitro). After the introduction of such ELISA tests, the frequency of false positive results decreased significantly and is about 0.02-0.5%.

A false positive result does not mean that the person is infected with HIV. In such cases, WHO recommends conducting another ELISA test (necessarily IV generation).

The patient’s blood is sent to a reference or arbitration laboratory with the mark “repeat” and tested using a IV generation ELISA test system. If the result of the new analysis is negative, then the first result is considered erroneous (false positive) and IS is not carried out. If the result is positive or questionable during the second test, the patient must undergo IB after 4-6 weeks to confirm or refute HIV infection.

Immune blotting

A definitive diagnosis of HIV infection can only be made after obtaining a positive immunoblotting (IB) result. To carry it out, a nitrocellulose strip is used, on which viral proteins are applied.

Blood sampling for IB is performed from a vein. Next, it undergoes special processing and the proteins contained in its serum are separated in a special gel according to their charge and molecular weight (manipulation is carried out using special equipment under the influence of an electric field). A nitrocellulose strip is applied to the blood serum gel and blotting (“blotting”) is carried out in a special chamber. The strip is processed and if the materials used contain antibodies to HIV, they bind to the antigenic bands on the IB and appear as lines.

IB is considered positive if:

according to American CDC criteria - there are two or three lines gp41, p24, gp120/gp160 on the strip;
according to the American FDA criteria, the strip has two lines p24, p31 and a line gp41 or gp120/gp160.

In 99.9% of cases, a positive IB result indicates HIV infection.

If there are no lines, the IB is negative.

When identifying lines with gr160, gr120 and gr41, IB is doubtful. This result may occur when:

In such cases, it is recommended to repeat the study using a kit from another company. If after additional IB the result remains doubtful, then observation is necessary for six months (IB is carried out every 3 months).

Polymerase chain reaction

A PCR test can detect the RNA of the virus. Its sensitivity is quite high and it allows detecting HIV infection within 10 days after infection. In some cases, PCR may give false-positive results, since its high sensitivity may also respond to antibodies to other infections.

This diagnostic technique is expensive and requires special equipment and highly qualified specialists. These reasons do not make it possible to carry out mass testing of the population.

PCR is used in the following cases:

to detect HIV in newborns born from HIV-infected mothers;
to detect HIV in the “window period” or in case of doubtful IB;
to control the concentration of HIV in the blood;
for the study of donor blood.

The PCR test alone does not make a diagnosis of HIV, but is carried out as an additional diagnostic method to resolve controversial situations.

Express methods

One of the innovations in HIV diagnostics is rapid tests, the results of which can be assessed within minutes. The most effective and accurate results are obtained using immunochromatographic tests based on the principle of capillary flow. They are special strips on which blood or other test fluids (saliva, urine) are applied. If antibodies to HIV are present, after a minute a colored line and a control line appear on the test - a positive result. If the result is negative, only the control strip appears.

As with ELISA tests, the results of rapid tests must be confirmed by IB analysis. Only after this can a diagnosis of HIV infection be made.

There are rapid home testing kits available. The OraSure Technologies1 test (USA) is FDA approved, available over the counter and can be used to detect HIV. After the test, if the result is positive, the patient is recommended to undergo examination at a specialized center to confirm the diagnosis.

Other tests for home use have not yet been approved by the FDA and their results may be very questionable.

Despite the fact that rapid tests are inferior in accuracy to IV generation ELISA tests, they are widely used for additional testing of the population.

You can take tests to detect HIV infection at any clinic, central district hospital or specialized AIDS centers. On the territory of Russia they are carried out absolutely confidentially, or anonymously. Each patient can expect to receive medical or psychological consultation before or after the test. You will only have to pay for HIV tests in commercial medical institutions, while in public clinics and hospitals they are performed free of charge.

Read about the ways in which you can become infected with HIV and what myths exist about the possibilities of getting infected in this article.

Which doctor should I contact?

To be tested for HIV infection, you need to visit a therapist and get a referral for testing. In addition, you can come directly to the AIDS Prevention and Control Center and get tested there anonymously. An infectious disease specialist or venereologist will also refer you for this examination if you suspect an HIV infection.

In what cases and when is HIV ELISA performed?

Description of the HIV ELISA test

How is HIV testing performed using ELISA?

HIV ELISA test: timing of testing

HIV ELISA in a month, two or several weeks: when to get tested?

Where can I get an ELISA test for HIV 1, 2?

What is HIV ELISA and its features

When taking tests, you always want to get only reliable answers. Especially when testing for immunodeficiency is carried out. It is in this case that the accuracy of HIV tests is important, because the future health of the person and his family depends on it. HIV testing is done in almost every clinical laboratory. To do this, it is enough to donate a small amount of blood and wait a few days before the result is issued. ELISA test for HIV is the most common analysis method that helps to detect antibodies to the virus, which confirms its presence in the body of the infected person.

What is ELISA

This research method uses an enzyme-linked immunosorbent assay, which is based on the detection of antibodies. This method has an immunochemical reaction, which allows you to see which antigen the antibody is associated with. This analysis is considered one of the most accurate and convenient. It is used even in cases where the PCR method after a viral load failed to obtain an accurate answer.

The most common heterogeneous ELISA variant. In it, the patient's blood is mixed with the antigen and antibodies are added to help create the molecular chain. It is in it that the virus protein can be detected and proven that HIV exists in the human body.

When is ELISA performed?

Since the virus is not visible immediately after possible infection, it takes some time for it to multiply and be detected. Only research can give a more reliable answer. Depending on the concentration of the virus in the body and how it enters, it may take a couple of weeks or several months to appear. No one knows exactly when it will appear; each infected person has an individual time frame.

Therefore, it is recommended to do the ELISA test several times. Basically, it is recommended to carry out it after 6 weeks, after 3 months and after six months. It is precisely this period, from the virus entering the body until it is detected, that will be the seronegative window. Therefore, during the window period, an ELISA test for HIV is performed. Foreign doctors recommend doing an HIV test after 3 months, ignoring the six-month test. But much depends on the ELISA itself and its generation. Moreover, people are constantly worried and afraid that HIV will not manifest itself during this time. To really be sure and reassure yourself, they take this test three times.

Features of ELISA

This research method was discovered several decades ago. Indeed, the first generation of ELISA was not so sensitive, which required multiple tests at different times. After all, only a high viral load helped detect HIV by ELISA. It was not very convenient; I had to live for a long time in worry and constant fear for my health.

Therefore, ELISA has not stood still since then. Even now, it continues to develop, looking for new opportunities for faster and more accurate research and detection of the virus. This will help detect it sooner after infection and start taking medications to suppress it earlier.

At the moment, there are already 4 generations of ELISA. The higher the generation, the more accurate and faster the analysis will be. Modern ELISA tests help detect the p24 antigen, which appears before the virus antibodies. This is what allows us to see the manifestation of the virus earlier than in previous years. Perhaps after some time several more generations will appear that will be able to detect HIV at the beginning of infection.

If the ELISA test is positive

In cases where the ELISA is positive for HIV, you should not panic. Perhaps the person did not heed the advice on preparation before taking the test, or he suffered from an acute viral infection. This is what can give such unwanted positive results.

In such a situation, an additional repeat test with other research methods is prescribed. The immunoblotting method is often used to look for antibodies to individual viral proteins. The reliability of such a study is quite high and allows us to accurately determine the presence or absence of the virus in the body.

Preparation for ELISA

In order for the ELISA test for HIV to be true and accurate, it is advisable to listen to the advice of doctors on preparing for the test. This helps to avoid false positive results and unnecessary unnecessary worries. Therefore, it is important to prepare the body in advance.

It is not recommended to drink alcoholic beverages immediately the day before taking the test. Ideally, this would take several days. Also, don't eat too much before the test. The last meal is possible 8 hours before donating blood for testing. They usually take it in the morning, so the last meal is dinner. And in the morning they donate blood on an empty stomach.

If a person has had an acute viral disease, the reliability of his tests will sharply decrease. It is advisable to consult a doctor about this or do a test a little later, when the body is completely freed from the residual effects of an acute viral illness. But in the case of a repeat test, a different method can be used to reliably verify the presence or absence of the virus.

Pregnancy and ELISA

Pregnant women must undergo some tests, including an ELISA test for HIV. But this time has its own characteristics, because pregnancy can affect the accuracy of HIV results. This is why a seemingly healthy woman receives a positive HIV test.

But do not despair and worry about your health and the well-being of your unborn child. Such false tests may not be the fault of the laboratory staff, but due to the special condition of the mother. Some processes occurring in her body at this time significantly affect the result.

It happens that a woman’s body perceives the baby’s body as a foreign object and begins to produce antibodies against it. If the period is quite short, and there are already a lot of antibodies, then miscarriages can often occur. Therefore, it is advisable to register at the very beginning of pregnancy.

Also, during this wonderful time for a woman, her body weakens somewhat, as does her immune system, and chronic diseases take advantage of this, trying to have a stronger impact on her health.

Because of such situations, false positive results occur. But don't worry. It is enough to take the test again and everything will become clear.

Where to get tested for HIV

Since the ELISA research method is common, it is used in every laboratory. Therefore, everyone chooses their own choice of place to donate blood for HIV. You just need to know the test appointment time and address.

If you wish, you can visit the AIDS Center and take the test there, because the work of this institution is aimed specifically at this disease and solving problems with it. Research in it is no different from research in other laboratories.

On average, it takes about 5 days to receive an analysis. But some laboratories can do it in 3 days. It is worth understanding that there may be cases when the response is delayed for a longer period. But this does not mean that the result will necessarily be positive. Perhaps some situation in the laboratory or a large influx of tests does not allow this to be done quickly.

If the ELISA test is positive, then a repeat test is prescribed. This is always done to eliminate possible errors on the part of the patient and the human factor of medical staff. In this case, research can be carried out using a different method.

If the repeated analysis yields a positive result, then you should consult a doctor. He will prescribe appropriate treatment and monitor the condition of the infected person. Drugs and dosage are selected individually for each person. It all depends on the viral load and the characteristics of the body.

If the tests are in doubt, a person can take them in several laboratories and then compare them when they receive the results. But cases of error are quite rare and the results are generally reliable. If one partner has been diagnosed with HIV, then it is advisable for the other to also undergo testing.

With proper treatment, the spread of the virus is suppressed and the person can live peacefully. If he does not tell about his illness, then no one will know, because doctors do not have the right to reveal medical confidentiality. But it is advisable to protect your loved ones and relatives by taking all safety measures.

HIV analysis using ELISA: accuracy, reliability

Human immunodeficiency virus is a serious diagnosis. Errors in diagnosis can lead to disastrous consequences. HIV ELISA is the most accessible research method. You need to figure out how effective it is.

What is ELISA

ELISA - enzyme immunoassay. The purpose of the ELISA method is to identify antibodies or specific antigens in biological material. Using the method, you can monitor the presence of viruses and other large molecules in a liquid. The research is used in the food industry, agriculture, and various fields of medicine. Enzyme immunoassay is widely used in the diagnosis of STDs. It helps detect HIV and other sexually transmitted infections. In this case, the “sandwich” method is used - this is a variant of ELISA for detecting antigens.

“Antigen-antibody” is the name of a system that determines the presence of antibodies, which serve as an indicator of the penetration of a foreign molecule. To identify these “tags,” the biological component is treated with enzymes. Enzyme immunoassay determines antibodies with % accuracy, the error is insignificant. It is 2 - 4%.

ELISA - a method for diagnosing HIV

I. ELISA test for HIV is the first stage of diagnosis. The highest concentration of virus cells is observed in the blood of an infected person. The antigens of the immunodeficiency virus are proteins p24, p15, p17, p31 and glycoproteins gp 41, gp55, gp66, gp120, gp160. To detect the viral protein, a portion of blood is taken from a vein. A sample sent for ELISA blood testing is treated with enzyme immunoassay reagents. Blood is donated strictly on an empty stomach. It is not recommended to eat fatty foods or drink alcohol 2 days before the test. You should stop taking antiviral drugs for 14 days.

Serum is isolated from the blood. It is applied to a special tablet with many small holes (96 pieces). A viral protein is added to the biological material. The plate is washed several times with enzymes. If antibodies and antigens begin to be produced during such treatment, it means that the virus was already present in the blood.

Advantages of the ELISA method:

relatively low cost;
high stability of reagents;
sensitivity;
carried out in a short time;
minimal influence of the human factor.

Modern ELISA test systems are produced according to international standards. This increases the accuracy of the method.

After the virus enters the blood, the latent (hidden) stage of development begins. The period before dangerous molecules begin to multiply and antibodies have not yet been formed is called the “seronegative window time.” There is no point in taking an HIV test at this stage. If infection occurs, the result will be false negative. How quickly the virus reveals itself depends on how many dangerous cells have entered the body. In case of unprotected sexual intercourse or transfusion of contaminated blood, this period will be minimal. For high reliability of HIV ELISA, the test is carried out three times. Deadlines for taking the ELISA test for human immunodeficiency virus:

in 6 weeks,
in 3 months,
six months later.

4th generation ELISA for HIV is a method that is most informative in the early stages of infection. It can be performed as early as 1 month after the suspected infection. The 4th generation HIV test is expensive compared to its 3rd generation counterpart. Therefore, in public medical institutions it is used as an additional diagnostic method. Test 3 is carried out free of charge; if its results cannot give an unambiguous answer, the therapist will refer you to a 4th generation ELISA test.

Important! Immediately after infection, a person becomes contagious. He is dangerous to others, even when he does not yet know about his diagnosis!

II. If HIV antigens are detected by ELISA, additional studies must be performed. These include polymerase chain reaction (PCR). The reliability of this method is 80%. PCR tests blood, semen and vaginal discharge. The biological fluid is broken down in a medical reactor and then treated with enzymes. As a result, data is obtained on the concentration of HIV cells in the liquid medium. Due to the large error (20%), if the result is positive, immunoblotting is additionally performed.

III. The next stage of diagnosis is the Combo test (or immunoblotting). This is a highly sensitive test (98% confidence), which is carried out if ELISA results are equivocal after 6 months.

Decoding ELISA results

Even if the result of the initial and repeated ELISA was positive, the person cannot be considered infected. There may be errors in the HIV test. Reasons for a false positive result:

chronic diseases,
long-term infectious diseases,
pregnancy.

If the immunoblotting test for HIV results in a positive (reactive) result, the person is considered HIV-infected, and a negative test means that he is healthy. Reactivity or viral load for HIV is characterized by the number of antigens per unit of blood. The norm is considered to be the number of antibodies to the virus from 5000 cells. If the number is within these limits or less, the virus is inactive. Even if a positive HIV status is further confirmed, a person will not notice changes in his health for a long time (years). If the reactivity is less than cells, this is close to normal. When their number increases, antiviral therapy should be started immediately.

Decryption time ranges from 24 to 48 hours. If you need to obtain information urgently (surgery is required), the period is reduced to 2 hours. Provincial medical centers do not always have the necessary reagents. The sample is taken at the place of application, then it is transferred to the regional center. Under such circumstances, the result can be found out in 1-2 weeks.

The result of an enzyme immunoassay is a table that lists antibodies and antigens. Opposite each there is a mark “+” or “-”. Sometimes a quantitative indicator per unit of blood is indicated.

A separate column shows the antigen avidity index. The percentage figure makes it clear when the infection began to develop.

What to do if the ELISA is positive

3rd and 4th generation enzyme immunoassays show with high confidence (98%) that a person is healthy. It is not enough to confirm a positive HIV status. If HIV antigens are detected in the blood during the first and repeated tests, the person receives a referral for immunoblogging. When research reveals that a person is HIV-positive, he should consult a doctor. He will determine the viral load and, after registration, select therapy. Over time, the virus cells adapt to the prescribed drugs. To monitor the effectiveness of treatment, an ELISA test is performed periodically.

Sometimes immunoblogging shows a false negative result. It is extremely rare that the immunodeficiency virus does not manifest itself for 6 months (or more). This is possible if a small amount of virus cells enters the blood. In 0.5% of the total number of cases, the infection can be diagnosed only after a year. In 99.5% of cases, within six months, an ELISA test will yield a reliable result. Even with highly accurate studies, there is still a 2% chance of error. We should not forget about the human factor. People tend to make mistakes. In order to exclude it, the test can be carried out in 2 different institutions.

An HIV blood test or HIV test includes several laboratory diagnostic methods that help determine the presence of the immunodeficiency virus (HIV), detect antibodies to its proteins (immunoglobulins) or antigens (virus proteins) in the patient’s blood, saliva or urine. The human immunodeficiency virus has a unique antigenic variability, which is associated with a high rate of transcription (reproduction), which makes both the diagnosis of HIV infection and its prevention difficult.

The basis for diagnosing HIV infection, like any other infectious disease, is:

epidemiological history,
characteristic complaints of the patient,
clinical picture of the disease,
data from laboratory research methods.

Once the diagnosis of HIV infection is established, in order to clarify the nature of the course of the underlying disease and secondary diseases, further examination of the patient is carried out and appropriate treatment is prescribed.

The severity of the disease is assessed by the level of virus concentration in the blood, the number of CD4 lymphocytes and the determination of the p24 antigen.

Main types of HIV diagnosis

Virological diagnostics is based on the detection of HIV in the patient’s tissues and biological fluids.

Polymerase chain reaction(PCR) is used to detect the virus and assess the viral load, which makes it possible to judge the effectiveness of specific treatment and predict the course of the infectious disease.

Serological diagnosis HIV infection involves the detection of viral antigens and antibodies in blood serum. Detection of antibodies to using ELISA (enzyme-linked immunosorbent assay) is the main method of laboratory diagnosis. All positive results are confirmed by immunoblotting. is based on the detection of antibodies in the blood and biological fluids of the subject. Used in cases where it is necessary to quickly obtain results.

Level of immunosuppression determined by the method of counting CD4 and CD8 lymphocytes, followed by determination of the CD4:CD8 ratio.

Each of the laboratory methods for diagnosing HIV infection is characterized by a certain sensitivity (% of correctly identified tests among obviously (+) samples) and specificity (% of correctly identified tests among obviously negative samples). HIV test results are interpreted as negative, positive or equivocal.

Rice. 1. In the photo on the left, HIV infects an immune cell (indicated in yellow). In the photo on the right is a lymphocyte infected with HIV. Elongated structures on the cell surface are caused by protein overproduction.

Rice. 2. The photo shows the process of release (budding) of virions from an infected cell.

Blood test for HIV. What you need to know

Any resident of our country can do a blood test for HIV anonymously and free of charge. But there are categories of people who are required to be tested for HIV. These include:

all donors of blood and its components, as well as tissues and other biological fluids;
persons who have undergone a transfusion or transplantation (carried out during the first 3 months after the procedure);
pregnant women;
persons injured as a result of the accident;
persons with clinical indications - fever, diarrhea, persistent cough and enlargement of more than 2 groups of lymph nodes, lasting more than 1 month, unexplained weight loss, AIDS-associated and opportunistic infectious diseases, somatic and oncopathology;
Foreign citizens;
persons at risk (drug addicts and those suffering from sexually transmitted diseases).

Anyone who has been exposed to HIV should be tested for HIV.

Rice. 3. A blood test for HIV in our country can be taken anonymously and free of charge.

Where to donate blood for HIV

An HIV test can be taken free of charge in health care institutions operating on a budgetary basis if you have a passport and health insurance. Doctors are required to maintain medical confidentiality. You can get tested free of charge and anonymously at the AIDS Prevention and Control Centers and get medical advice there before and after the examination. HIV testing is carried out on a paid basis in commercial medical institutions. Any person temporarily residing in this territory can take an HIV test.

The laboratory will do a blood test for HIV using the enzyme immunoassay method (ELISA).

Anonymous HIV test

In public health institutions (clinics and hospitals), you cannot anonymously take a blood test for HIV. Information about the results of the study will be known to a narrow circle of doctors who are obliged to maintain medical confidentiality.

Anonymous testing rooms exist at the AIDS Centers, where each test is assigned a number.

Rice. 4. Test tubes with blood are sent for serological testing.

Forced HIV test

There are four population groups for which HIV testing is mandatory, but not forced:

Donors of blood and other biological material.
When applying for work in institutions where the employee may have contact with obviously infected material and patients.
Foreign citizens upon receipt of visas for residence (more than 3 months) on the territory of the Russian Federation.
If there are clinical indications for persons in prison.

Forced testing of the population for HIV is futile and contrary to respect for human rights. Forced testing of the population in the Russian Federation is illegal.

Rice. 5. HIV testing of convicts is carried out according to clinical indications.

How much does an HIV test cost?

In government institutions, HIV testing is free, in private clinics it is paid:

The cost of ELISA ranges from 400 to 800 rubles. The answer will be ready after one day. There is an urgent diagnosis, when an answer can be received within 2 hours.
The cost of an HIV test using the immunoblot method ranges from 3 to 5 thousand rubles. The result will be ready in 4 - 7 days.
The cost of an HIV test using the PCR method is 10 - 12 thousand rubles. The result will be ready in 10 - 14 days.

How long does it take to test for HIV?

In government agencies, the deadline for receiving HIV test results is:

When using 3rd generation ELISA, the results give the most reliable results 12 weeks from the moment of suspected infection.
When using 4th generation ELISA – 6 weeks.
When using PCR - 4 weeks.

How to get tested for HIV

It is necessary to take an HIV test no earlier than 3 to 4 weeks after the suspected infection.
Testing is carried out no earlier than 8 hours after eating.

The only liquid you can drink is plain water.

For analysis, 3 - 5 ml of blood is taken from the ulnar vein, for which a regular syringe or needle with a pump is used.
Before transportation to the laboratory, blood serum can be stored in the refrigerator for up to 7 days. Without refrigeration no more than 30 minutes after collection.
Transportation of tubes with blood serum is carried out in special thermal containers at a temperature of +4 - +8 o C.

Rice. 6. To test for HIV, it is necessary to collect 3 - 5 ml of blood taken from the antecubital vein - for which a regular syringe (photo on the left) or a needle with a pump (photo on the right) is used.

When blood is taken from a vein, it is impossible to become infected with the human immunodeficiency virus.

False-positive HIV test and other types of test results

HIV test results can be interpreted as positive, negative or equivocal.

Questionable test result for HIV is obtained when there are antibodies in the blood serum that cross-react with proteins of the human immunodeficiency virus. In this case, the analysis is repeated, and during its conduct more specific test systems will be used. If a questionable result persists, testing should be carried out every 1 to 3 months for six months.

Test positive for HIV(seropositive) indicates the presence of antibodies to the virus in the blood of the person being tested. In this case, the enzyme-linked immunosorbent assay (ELISA) is repeated and, if a second positive result is obtained, it is confirmed by an immunoblotting test with the same blood sample.

Negative HIV test result(seronegative) indicates the absence of HIV infection, or the infection occurred quite recently and antibodies have not yet been developed in the blood of the subject (the “window” period). In this case, the examination should be repeated after 3 and 6 months.

False positive HIV test result is registered when its cause was not the human immunodeficiency virus, but pregnancy, an autoimmune disease, allergies, any other infectious disease, a recent vaccination, oncopathology, organ transplantation and even ordinary food (seeds, spicy, fatty and sour foods eaten the day before, and even highly carbonated mineral water). A large number of false positive results are obtained when testing at home.

False negative HIV test result indicates that the virus is present in the patient’s blood, but antibodies have not yet been developed. When conducting a PCR analysis, a false negative result can be obtained in HIV-infected patients during the period of specific treatment, when the concentration of viruses in the blood is so low that it leads to the failure of the test system. In most cases, a false negative result is obtained due to a technical error or defect in the test system, which is extremely rare due to strict quality control at all levels.

An HIV test should be postponed for at least two weeks after an infectious disease or vaccination.

Rice. 7. Carrying out a serological blood test.

Test systems that determine the presence of antibodies to HIV

By testing for antibodies to the human immunodeficiency virus, the body's response to infection is assessed. For this purpose, an enzyme-linked immunosorbent assay (ELISA) is used to detect antibodies to viral proteins and a confirmatory immunoblotting analysis (Western blot), which determines the reaction of antibodies to viral proteins.

Antibodies to HIV

Human immunodeficiency viruses have antigenic properties and, when they enter the human body, cause the synthesis of antibodies - specific immunoglobulins. Using modern test systems, the class of immunoglobulins (antibodies) can be determined in the blood serum and other biological fluids of an HIV patient. IgM class immunoglobulins appear before everyone else (a week after infection). Their growth is observed within a month and then they persist for about 30 days. IgG class immunoglobulins circulate in the blood for several years. Their detection is an indicator of the presence of HIV infection.

Antibodies to HIV appear within 2–4 weeks. after infection and then they are detected in the blood throughout the entire disease.

"Window" period for HIV

Antibodies are not immediately produced in the body of an infected person. At first, HIV infection does not manifest itself in any way. Antibodies appear in the blood on average 2 - 3 months from the moment of infection (from 2 weeks to 6 months). This period is called the “window”, when tests for antibodies are still negative, but the viruses multiply intensively, and the patient himself becomes dangerous in terms of infecting contact persons. An infected person can be identified after a shorter (1 - 2 weeks) period after infection, for which polymerase chain reaction (PCR) is used. However, due to its high cost, this type of study is not used for screening.

Enzyme immunoassay for diagnosing HIV

In 90 - 95% of infected individuals, antibodies appear in the blood serum 3 months after infection. In a small proportion of patients (5 - 9%) antibodies appear in the period from 3 to 9 months and in 0.5 - 1% - in more than late dates. In the terminal stage of AIDS, the number of antibodies decreases significantly, and in some cases disappears completely.

Since 1985, this technique has been used in the Russian Federation for the purpose of mass research. It is easy to implement, shows fairly accurate results, and is cheap compared to other methods. Due to the possibility of obtaining false-positive results, all positive results are examined twice, after which the patient’s blood serum is examined with a confirmatory test - an immunoblot. This uses the same blood sample. If there are 2 positive results using ELISA and immunoblot in one sample, a diagnosis of HIV infection is made.

In the Russian Federation, 4th generation ELISAs are usually used. The study is carried out to obtain the total spectrum of antibodies against HIV proteins (antigens) - p24 and gp160.

The test sees both antibodies that are produced by the patient’s body and p24 antigens (virus proteins). The window period for 4th generation tests is shorter. Within a month you can get reliable results. However, according to Russian healthcare experts, terms of 6, 8 or 12 weeks are more reliable.

Rice. 8. The photo shows enzyme immunoassay analyzers.

Rice. 9. The photo shows an automatic enzyme immunoassay analyzer.

For the initial examination of groups of people in order to detect HIV infection, only the ELISA method is used.

Immunoblotting method

The immunoblotting method is more accurate than ELISA; according to most experts, it is the reference method. With its help, antibodies to HIV proteins are detected in blood serum. The technique is used to confirm the results obtained during ELISA. Has high specificity. False positive results are rare. The reliability of the results obtained reaches 99%. Immunoblotting is an expensive technique and requires high specialization of the specialist conducting the study. Questionable results may be obtained.

The method is based on the separation of HIV antigens (proteins) using electrophoresis based on molecular weight. Antibodies against capsid proteins are the first to be detected during infection. Gag"(p24 and p17) and the precursor p55. Following them, antibodies against supercapsid proteins appear. Env"(glycoproteins gр 160, gр120, gр41 and proteins р88) and non-structural proteins "Pol" (р31, р51 and р66). In some cases, antibodies against genes can be detected " vpu», « vpr», « vif», « tat», « nef», « rev», « tat».

The blood serum of patients with HIV-1 and HIV-2 contains antibodies to all viral proteins, but to confirm the diagnosis, only antibodies to proteins p24, gp41, gp120 and gp160 are detected in HIV-1, and antibodies to proteins gp105, gp140 and gp140 in HIV-2. gr36.

If there are 2 positive results using ELISA and immunoblot in one sample, a diagnosis of HIV infection is made.

Rice. 10. Apparatus for conducting immunoblot research.

Rice. 11. The diagnosis of HIV infection is made in the presence of 2 positive results using ELISA and immunoblot in one sample.

Test systems for counting CD4 lymphocytes

One of the immunological tests used for HIV infection is the method of counting CD4 and CD8 lymphocytes in the blood.

CD4 lymphocytes (T helper cells) are affected by immunodeficiency viruses. The gradual depletion of their population leads to a decrease in immunity and the patient’s body ceases to resist infection. CD4 lymphocyte counts are performed by flow cytometry using automated analyzers or manually using optical or fluorescence microscopy. The number of CD4 lymphocytes determines the time of initiation of specific treatment (antiretroviral therapy) and the prevention of opportunistic infections, and evaluates the effectiveness of treatment.

When the number of CD4 lymphocytes in the blood serum is 500 or less per 1 ml, it indicates the development of immunodeficiency.
When the number of CD4 lymphocytes decreases to 200 per 1 ml (the norm is from 600 to 1900 cells per 1 ml), acquired immunodeficiency syndrome (AIDS) develops.
When the level of CD4 lymphocytes decreases to 50 or below per 1 μl, AIDS enters the terminal stage.

The proportion of CD4 lymphocytes among all lymphocytes is normally about 40%. A decrease in the rate to 20% indicates the development of AIDS.

CD8-lymphocytes(T-killers, in English. killer- killer) destroy HIV viruses by cytolysis. Their proliferation (increase in number) depends on the activity of T helper cells. During HIV infection, the number of CD4 and CD8 lymphocytes decreases, but the level of CD4 lymphocytes decreases most of all. The normal CD4/CD8 ratio is 1.5 - 2.5. With a decrease in the number of CD4 lymphocytes, a decrease in the index is observed.

Its value less than 1 indicates a developed immunodeficiency; with a ratio of 0.6 - 0.8, AIDS develops.

Upon receiving positive test results, a person must register with the government agency Center for Prevention and Control of AIDS, where his condition will be monitored and adequate specific treatment will be prescribed.

Rice. 12. In the photo, automatic flow analyzers are used to count CD4 lymphocytes in the blood of the person being studied.

HIV test using PCR

In recent years, a molecular genetic method for diagnosing HIV infection—polymerase chain reaction (PCR)—has become increasingly widespread. With its help, the genetic material of the pathogen is determined - RNA - already 1 - 2 weeks after the alleged infection, and the high sensitivity of the test allows you to detect RNA viruses even if there are only a few of them in the test material. This technique is expensive and therefore is not currently used for screening. In addition, a significant problem with the study is the possibility of obtaining false positive results.

The essence of the PCR technique for HIV

The essence of this technique is to obtain multiple copies of the virus RNA (nucleic acid), which are subsequently identified both by their characteristic structure and with the help of labeled enzymes or isotopes.

Possibilities of PCR for HIV infection

Using PCR, you can resolve questionable results obtained when using the immunoblotting technique, diagnose HIV infection in the early stages (as early as 1-2 weeks after the suspected infection), monitor the effectiveness of antiretroviral therapy, and determine the stage of the disease.

Rice. 13. In the photo on the left is a normal T-lymphocyte, on the right is a T-lymphocyte infected with HIV. Multiple bubbles are visible, between which newly formed viruses (small rounded formations) have appeared. Using PCR, HIV infection is detected within 1 - 2 weeks after the suspected infection.

Advantages of the PCR technique for HIV

Using PCR, it is possible to detect the virus itself and its quantity.
Possibility of use in children under one and a half years old.
Evaluate the effectiveness of treatment.
Determine the severity and prognosis of the disease.

Disadvantages of PCR technology for HIV

High cost of research.
Availability of specialized laboratories.
Duration of obtaining results (up to 4 weeks).

Who needs PCR?

Receiving the result within 7-10 days for persons in case of suspected infection, when a result obtained in a short time is desired.
To determine the start date and evaluate the effectiveness of the treatment.
PCR is performed on infected pregnant women 4 weeks before birth in order to decide on the use of cesarean section.
Newborns from infected mothers. A positive result obtained twice indicates that the child is infected.

Under normal conditions, PCR is not used for screening and diagnosing HIV infection.

RNA PCR and DNA PCR. What is the difference

RNA PCR proves the presence of the immunodeficiency virus in the blood and the volume of detected RNA. This study is used in diagnosed individuals to evaluate the effectiveness of therapy.
Using DNA PCR, the presence of the virus in mononuclear cells in children is determined when antibodies to the human immunodeficiency virus in the mother prevent the use of the ELISA method.

The viral load is determined by counting the number of RNA copies in 1 ml of blood plasma, which makes it possible to determine the stage of the disease, analyze the specific treatment provided, and determine the severity and prognosis of the disease. The higher the viral load, the fewer CD4 lymphocytes are recorded in the blood plasma.

Interpretation of results:

RNA is either not detected, or the number of RNA copies is less than 20 per ml. plasma.
RNA was detected at the limit of sensitivity - less than 20 copies/ml.
RNA from 20 to 10 6 copies in 1 ml of blood plasma indicates the reliability of the result.
RNA copies greater than 10 6 ml are the upper limit of the linear range.

An increase in the viral load in a patient with HIV infection by three or more times is a clinically significant result.

Viral load monitoring is carried out every 3 months in patients who are not yet receiving treatment. If antiretroviral therapy is started, control is carried out after 2–8 weeks.

Rice. 14. PCR has become increasingly popular in recent years.

Rice. 15. Amplifiers for PCR.

An HIV test must be carried out in the early stages of infection and periodically during the disease, which will ensure timely administration of antiretroviral therapy to prevent the development of dangerous infectious and oncological processes.

Virus cultivation

Viruses, its RNA, DNA, antigens and antibodies can be detected not only in blood serum, but also in sperm, saliva, vaginal contents, etc. HIV is cultivated in a culture of lymphocyte cells. The technique is highly sensitive and specific (up to 100%), but the high cost of the study does not allow its use in everyday laboratory work.

Complete blood test for HIV

As a result of damage to the hematopoietic organs by human immunodeficiency viruses, inhibition of hematopoiesis is observed, which is manifested by a decrease in the number of lymphocytes (lymphopenia), neutrophils (neutropenia), platelets (thrombopenia) and anemia. In addition, the destruction of cell populations is influenced by autoimmune processes that develop in HIV-infected patients. IgG immunoglobulins predominate in the blood serum of patients.

Rice. 16. Taking blood from a vein and finger for testing.

Today, anyone can take an HIV test anonymously and free of charge in a matter of minutes, and modern equipment and trained personnel allow you to get the most accurate results.

Thanks to the development of modern medicine, when making a diagnosis, a doctor no longer needs to focus on indirect manifestations of diseases or conduct multi-stage laboratory tests. It is enough to conduct one analysis that will confirm or refute the alleged initial diagnosis.

This method is enzyme-linked immunosorbent assay (ELISA) - this study allows you to detect specific antibodies and antigens characteristic of various pathologies, which greatly speeds up the diagnosis.

ELISA analysis is a laboratory test (method) that helps determine the presence or absence of certain antibodies in the body to fight the virus and their quantity.

The basis of the study is the natural reaction antigen (an object harmful to the body) - antibody (a protein that destroys harmful objects), which makes it possible to detect the presence of various viruses and bacteria.

ELISA is a natural immune response of the body - the interaction of an antibody with the corresponding antigen. So, during ELISA, antigens or antibodies are added one by one to a test tube with the material, after which the concentration of the resulting antigen-antibody complexes is determined.

If matches are formed, then immune complexes arise, then an enzymatic reaction of the dye with the combined molecule occurs. It is thanks to the color change during enzymatic indication that the disease is identified after examining the level of the determined compound.

Types of immunoglobulins

Human immunoglobulins are differentiated into several classes that differ from each other in the properties, structure and antigenic characteristics of the heavy chains (H chain). All mammals, including humans, have five H-chains, which determine the belonging of immunoglobulins to the corresponding class: G, M, A, D, E.

Each class differs from each other in biological properties, and the ability to bind antigens, and the speed and strength of the connection with the molecule.

The functions of each immunoglobulin (Ig) are different:

Quantity in the body

Functions

Half-life (days)

Meaning

70%

Form passive immunity in the newborn;

necessary for immune response

improve phagocytosis,

21-24

provide long-term humoral immunity against infectious diseases

5-10%

needed to activate phagocytosis,

capable of binding 5 antigen molecules,

Provides the primary immune response

10-15

Neutralizes toxins and viruses

needed for the formation of early immunity

The emergence of immunoglobulins occurs along a peculiar “chain” - lgM lgG, this is how the body reacts to the appearance of an antigen in the body. During laboratory diagnostics, the concentration of three main immunoglobulins is assessed - G, M, A.

Indications for immunoglobulin testing

ELISA analysis is becoming more and more popular every year.

Such a study speeds up the diagnosis, and this is very important for the treatment of pathologies such as:

viral hepatitis;
HIV infection;
cytomegalovirus,
Epstein-Barr virus,
herpes virus,
rubella,
tuberculosis,
salmonellosis,
dysentery,
tick-borne encephalitis,
Helicobacter bacteria,
borreliosis,
tetanus,
syphilis,
diphtheria,
leptospirosis,
chlamydia,
ureaplasmosis,
mycoplasmosis,
whooping cough.

flatworms
roundworms
histolic amoebae,
liver tremades,
Giardia,
toxoplasma,
trichinella,
fluke,
cestodoses.

ELISA is a unique marker of autoimmune pathologies and malignant neoplasms.

Preparing for the test

When preparing for the study, you should adhere to the following rules:

Doctors also recommend adhering to a special diet - excluding fatty and fried foods, and if the test is carried out for hepatitis, then it is necessary not to eat any orange vegetables and especially citrus fruits. You should donate blood in the morning on an empty stomach.

False-positive analysis occurs due to unfulfilled recommendations, especially the consumption of fatty foods, which leads to too high a concentration of triglycerides in the plasma, which causes the ELISA conductivity to decrease.

Sample collection procedure

Whole blood, serum or venous blood plasma can be used as the test material. The material is collected, usually from the ulnar vein, using a disposable needle and a vacuum tube; 5-10 ml of blood is required.

To ensure the accuracy of the result, it is important to adhere to the correct sampling technique - the puncture of the vessel itself and the surrounding tissues must be performed in one manipulation, therefore a short needle with a large diameter is used, so that the opposite wall of the vein is not injured and red blood cells are not damaged.

Also, to maintain the integrity of red blood cells, it is necessary for blood to flow down the walls of the test tube.

During storage of the material, possible ionization should be avoided; in addition, the material should not come into contact with residual disinfectants, therefore only a disposable plastic tube is used, marked with the patient’s name, date and time of delivery of the material.

If short-term storage of the test material is necessary, then a refrigeration chamber with a temperature of 2-4 o C is used, if longer storage is necessary, then the material is frozen at a temperature of -20 o C.

How the analysis is done

After preparing the material under study, the laboratory assistant begins the necessary manipulations. For this purpose, a number of special sets of antigens are used, which have the ability to provoke the body’s response to an irritant, these are various infections, hormones, and allergens.

The expected antigen-antibody reaction looks something like this:

The primary reaction is a detected Ig (Ab) and a purified pathogen antigen (Ag).
To detect the resulting immune complexes, a new immunological reaction follows, where the antigen is a bound specific Ig, and the antibody for it is a conjugate Ig (Ab).
The last stage is an enzymatic reaction, together with a catalyst molecule of the conjugate. The substrate is a chromogen (not colored), which becomes colored during the reaction, and the intensity of the color is determined by the quantitative indicator of immunoglobulin in the sample.

At the moment, many different ELISA options have been developed, but there is no clear classification of them. Typically, methods are considered based on their division into hetero- and homogeneous - all phases of analysis occur using a solid phase or using only a solution.

Modern clinical diagnostic laboratories usually use heterogeneous (solid-phase) ELISA, in which the solid phase means the absorption of antigens or antibodies on the solid surface of special wells located on a polystyrene microplate; the method is divided into direct and indirect ELISA.

With direct ELISA, the introduced antigen is fixed during the incubation process on the surface of empty wells; for this, the test material is placed in clean wells for 20-25 minutes, this is necessary for the antigen to attach to their surface. After this, the required antibody is added. Next, the material remains for a certain time to form bonds.

Antibodies are always added in excess, so even if they are present, unbound antigens remain in the sample, and if there are no antigens at all, then there will be no connections. To remove “extra” antibodies, decantation is performed, after which only those antibodies that have created a bond with the antigen remain.

This is followed by an enzymatic reaction - adding a solution with an enzyme to the wells, after which the resulting bonds are colored.

In the indirect ELISA method, antibodies are used that are pre-combined with the substrate of the enzymatic reaction; in this case, the connection of antibodies with the antigen occurs during the incubation process, after which the mobilization of bonds on the surface of the wells occurs, and the conjugate and substrate-chromogenic reagent added afterwards color the reaction.

Thus, the main difference between the indirect and direct methods is not the adhesion of the material to the surface of clean wells, but the binding to the antigen immobilized on the plate.

The reaction is stopped using specialized devices, then each well is subjected to a photometric process, followed by a comparative description of the result obtained with previously conducted control samples.

If an increase in optical density is detected in the sample, then the concentration of specific antibodies in the test result is also overestimated.

When will the analysis be ready?

The study does not take much time; from blood sampling to receiving the result, it takes from 1 to 10 days, depending on the diagnostic measures.

Test results and their interpretation

The diagnostic result form received by the patient indicates a negative or positive result for certain classes of immunoglobulins, and a quantitative indicator of various classes of antibodies is also indicated.

Various interpretations of the results are possible:

IgM (+) (IgA, IgG were not determined) – healing process;
IgM (-);IgG (+), IgA (+) – chronic infectious pathology;
IgM, IgG, IgA (all with – meaning) – lack of protective mechanisms to infections;
IgG (+/-) and IgA (+/-), IgM (+) – acute process;
IgM (-), IgA (-), IgG (+) – post-infectious immunity;
IgM, IgG, IgA (+) – chronic pathology in the acute stage.

So, for example, if IgG and IgM were detected, then the patient may have one of the following diseases:

viral hepatitis;
cytomegalovirus;
herpes;
chicken pox;
chlamydia;
staphylococcal or streptococcal infection.

Enzyme immunoassay is often prescribed for hormonal studies; the norms are shown in the table:

	Hormone name	Floor	Norm
1	thyroglobulin	m/f	Up to 70 IU/ml
2	thyroxine	m/f	64-146 nmol/l
3	triiodothyronine	m/f	1.8-2.8 nmol/l
4	Free thyroxine	m/f	11-25 pmol/l
5	Free triiodritonin	m/f	4.49-9.3 pmol/l
6	Testosterone, dehydrotestosterone	AND	0.5-10 mU/l

ELISA analysis is a diagnostic test that allows you to assess the likelihood of the formation of oncological pathologies. However, interpretation of the results is carried out only by the attending physician.

Meaning of test results

ELISA is suitable for detecting various forms of sexually transmitted infections, including syphilis, and is often used for screening pregnant women.

Thanks to this study, you can find out how long ago the infection occurred and the stage of the disease at the time of the study:

immunoglobulins M indicate the duration of the disease;
IgA - the patient became infected more than 30 days ago;
IgG is detected at the “peak” of diseases, or at the moment when therapy has recently ended.

During the study, the wells on the plate with a negative indicator remain colorless, and the positive ones turn bright yellow. If the color of the positive wells does not match the color of the control, then the result is considered questionable and a repeat test is necessary.

Enzyme immunoassay is the first step in diagnosing HIV. The analysis cannot be carried out immediately after suspected infection; it is necessary to wait until the end of the incubation period (from 14 days to 6 months).

During the analysis, antibodies to HIV-1 and HIV-2 are determined, class G antibodies are searched for, which usually appears at a later stage, and class A and M antibodies are detected in the early stages (during the incubation period).

if the first test gives a positive result, then the blood is rechecked again by another laboratory technician;
a repeated positive result presupposes a retake of the material,
If the result is repeated, the patient is prescribed immunoblotting.

The final conclusion about the presence of HIV infection is issued only after the result of immunoblotting.

ELISA is also used as a diagnostic test for tuberculosis, but even if the patient has antibodies to this pathology, this does not always confirm the presence of tuberculosis, so ELISA is often used as a clarifying technique, or to diagnose a latent extrapulmonary form.

IgG - chronic stage of invasion

IgA – infection occurred more than 30 days ago

IgG – invasion is in the acute phase

IgG – confirms the diagnosis and shows the effectiveness of therapy

Pros and cons of analysis

ELISA has many advantages, which explains its popularity among doctors and patients, these are:

high accuracy of results,
affordable price,
quick result,
identifying the stage of the disease,
disease control over time.

However, along with the advantages, there is also a disadvantage - in rare cases, the analysis can be false positive or false negative.

Why the result may be unreliable

Errors as a result can occur due to technical violations; the analysis can also be unreliable in people with certain chronic diseases (rheumatoid factor) which are characterized by the production of specific antibodies.

The final result is also influenced by the patient’s use of medications and metabolic disorders. For these reasons, a positive result for HIV and oncopathology requires repeat samples.

Cost of the study

The price of ELISA varies depending on the direction of diagnosis (RUB):

hepatitis 250 -900;
viruses – 250 -1000;
HIV – 250-350;
helminthic infestations – 280 – 900;
syphilis -150-250;
fungal infections 400-500.

Article format: Lozinsky Oleg

Video about ELISA analysis

How is ELISA analysis performed: