Ifa blood for HIV. FAQ: HIV testing Ifa 4th generation 3 weeks HIV

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

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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 HIV antibodies 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.

1. 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.
2. 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 most patients, antibodies to HIV are detected 6–12 weeks after infection using first-generation test systems and 3–4 weeks using third-generation test systems that work on the sandwich ELISA principle with two antigens. However, HIV infection is detected already 2 weeks after infection by testing for p24 antigen and already after 1 week by testing for viral RNA. In other words, the window period can be reduced to 2 weeks or more using a comprehensive diagnostic approach. The p24 capsid antigen appears in the blood during rapid viral replication in the acute febrile phase of HIV infection and during this period is easily detected using a simple and relatively cheap ELISA.

If the task is to identify all HIV-infected people, including those with early stages of infection, then it is necessary to use the entire arsenal of tests: for antibodies, for antigens and for RNA. However, testing for viral RNA is expensive, labor intensive, and unavailable to most laboratories. Yet those laboratories that have ELISA equipment are able to detect most cases of HIV infection, provided that samples are tested for both HIV antibodies and p24 antigen.

At the end of the 1990s. test systems for parallel ELISA for HIV antibodies and p24 antigen appeared, eliminating the need for separate tests. A new generation of combined test systems has been developed and is being introduced for the simultaneous detection of HIV antibodies and HIV antigens.

The advantage of combined assays is that they take less time, require less labor, and are more cost-effective than separate assays. Combined test systems have high analytical sensitivity both due to the use of sandwich ELISA with two antigens to detect antibodies to HIV, and due to the simultaneous detection of p24 antigen.

There are currently 8 fourth-generation combination test systems on the market that have undergone clinical trials: VIDAS HIV DUO Ultra (bioMérieux; Marcy-l'Etoile, France); Enzymun-Test-HIV-Combi (Boehringer; Mannheim, Germany); Vironostika HIV Uni-Form II Ag/AB (Organon Teknika; Boxtel, the Netherlands); AxSYM-HIV Ag/AB (Abbott Laboratories; Abbott Park, IL, USA); Enzygnost HIV Integral (Dade Behring; Marburg, Germany); Genescreen Plus HIV Ag-AB (Bio-Rad), and COBAS Core HIV Combi (Roche Diagnostics; Mannheim, Germany); Elecsys-HIV Combi (Boehringer; Mannheim, Germany). The latest test system uses an electrochemiluminescent sandwich method with two antigens; analysis takes 18 minutes; specificity based on tests in hospitalized patients is 99.8%. This test system allows you to diagnose HIV infection 5 days earlier than the most sensitive test systems for HIV antibodies. There is another unbranded combination test system for antibody and p24 antigen ELISA with a sensitivity of only 99.5% and a specificity of 94.8%.

A combined antibody and antigen test to detect recent and long-term HIV infection is warranted not only when testing blood donors, but also in many clinical situations. Early diagnosis of HIV infection by detecting the p24 antigen allows for immediate treatment, counseling of the patient and taking measures to reduce the risk of transmission of infection. Thanks to their ability to detect p24 antigen, fourth-generation test systems make it possible to diagnose HIV infection in the early stages. These test systems are very useful for diagnosing recent and long-term HIV infection in hospital and independent clinical laboratories and diagnostic centers (both public and commercial). Such institutions are often visited by patients whose risk of HIV infection is significantly higher than that of blood donors. For early detection of HIV infection in such patients, test systems with high analytical sensitivity are required.

It is important to note that the high analytical and epidemiological sensitivity of most fourth-generation test systems, proven in tests on patients from different populations, patients with seroconversion and patients with different subtypes of HIV, makes these test systems indispensable for the diagnosis of both recent and long-term HIV infections in a variety of situations. For example, in clinical laboratories of public health institutions, blood testing for HIV antigens is not usually carried out (this is the prerogative of blood transfusion stations), and therefore cases of recent infection may be missed with standard testing for HIV antibodies. It has been shown that identifying infection in the early stages provides a basis for timely initiation of antiretroviral therapy, which increases its effectiveness. In addition, it becomes possible to promptly consult the patient, properly organize his management and prevent the transmission of HIV infection.

Express tests: This is a class of test systems that provide results faster than in 30 minutes. Rapid tests for detecting specific antibodies to HIV appeared in the late 1980s, and in the early 1990s. gained popularity. Thanks to improvements in production technology, rapid tests have become no less accurate than ELISA (provided that the analysis is carried out carefully by a qualified employee). However, due to the supposed simplicity of rapid tests, staff often make mistakes. For example, when adding reagents, pipettes are not always held vertically (as indicated in the instructions), which violates the ratio of reagent volumes. Another source of error is the desire of many laboratory technicians to simultaneously analyze several samples. Because of this, the timing of the analysis stages is not maintained.

When performed correctly, rapid HIV antibody tests provide reliable results and can be used in a wide variety of health care settings and clinical situations. In particular, they are used in emergency departments, doctors' offices, outpatient clinics, pathology departments, morgues, blood transfusion centers, and anywhere where urgent testing for HIV is required (for example, after contact of a health care worker with a possible source of infection).

Rapid HIV tests are indispensable for testing women in labor who have not received prenatal care (i.e., women in labor whose HIV status is unknown). It has been shown that antiretroviral therapy (in particular, zidovudine) effectively reduces the risk of vertical transmission of HIV and that such treatment is necessary as early as possible for the mother and then the newborn. Rapid testing of a pregnant woman for HIV in the prenatal period allows, if antibodies are detected, to begin treatment before birth.

Timely diagnosis of HIV infection becomes an extremely important measure, since early initiation of treatment can largely determine the further development of the disease and prolong the patient’s life. 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:

• ELISA test system (screening analysis);
• immunoblotting (IB).

Other methods can also be used for diagnosis:

• rapid tests.

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;
• infectious diseases caused by the Epstein-Barr virus;
• state after ;
• 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:

• oncological diseases;
• pregnancy;
• frequent blood transfusions.

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 10-15 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 10-15 minutes a colored and control strip appears 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 becoming infected.

About half of all questions that arise on the topic of HIV are related to HIV tests and their reliability. Nowadays, the ELISA test (enzyme-linked immunosorbent assay) is used everywhere as a primary (screening) test for HIV. Its peculiarity is that it determines not the presence of the virus itself in the body, but the presence of antibodies to it (which, however, is complete proof that the virus itself is present, even if the virus itself is not detected by PCR due to the low viral load) . But the main problem is that antibodies to HIV do not appear immediately after infection, but with some delay. Therefore, a situation is possible when infection has already occurred (and transmission of HIV to other sexual partners is possible), but the HIV test still shows nothing. This period is called the seroconversion period, seronegative window, or simply the window period. And naturally, the main question on this topic is how long this window period lasts or, in other words, how long after a possible risk of infection, a negative ELISA test result can be considered completely reliable.

And the answer to this question is really very important for those who have had a risk of infection, because it is this period that determines how long they will have to languish in anxious anticipation until the moment when the test can be done.

You must understand that if infection has occurred, the ELISA test will most likely show it much earlier than the seronegative window, but if there is no infection, then you can be completely sure of this only as a result of a negative test after the end of the window period.

If you look for this information on the Internet, you can find very different and contradictory data. A window period is mentioned from 2 months to six months, a year and, sometimes, even more. And the fact is that ELISA tests have been used for quite a long time, and several generations have changed since then. The first tests were quite insensitive, and for them to “work” an increased concentration of antibodies was needed. It is from here that for a long time a period of 6 months appeared as a seronegative window.

Currently, 4th generation ELISA tests, or so-called combo tests, are widespread almost everywhere. In addition to the presence of the antibodies themselves, they also determine the presence of the specific antigen p24, which, in the event of infection, appears several weeks before the antibodies. This allows us to assert that, that the seronegative window period for modern ELISA tests does not exceed 3 months . In other words, a negative test taken 3 months after the risk of infection will be completely reliable. Although, according to existing statistics, within the first 22 days after infection, ELISA is already positive in 50% of all cases, and during the first 6 weeks after infection, ELISA is already positive in 95%. (Source Current Medical Diagnosis and Treatment 2008, page 1162).

Therefore, the optimal scheme for taking an HIV test is as follows: 6 weeks after the risk (the reliability of the negative test is 95%) and again, for guarantee, 3 months after the risk (the reliability is almost 100%).

There is information that after the period of the acute stage of HIV, the p24 antigen may disappear. But you need to understand that if this happens, then by this time antibodies to HIV have already been developed and therefore the ELISA test will in any case be positive and reliable.

Why does the period of 6 months still appear so often on the Internet, on helplines and other sources? One of the reasons is simply outdated data that related to ELISA tests of earlier generations. Another thing, perhaps, is that, as far as I know, the period of 6 months is still present in the official recommendations for doctors. And therefore, during official consultation, most often for reinsurance and for formal compliance with these recommendations, they talk about a 6-month window period, forcing people to wait and suffer for half a year, instead of 3 months.

An increase in the seroconversion period is possible only in some exceptional and therefore very rare cases: if a person takes post-exposure prophylaxis against HIV or immunosuppressive drugs - immunosuppressants (no other drugs can affect the seroconversion period), or in the case of severe diseases of the immune system (no other diseases either do not affect the window size). But, in the latter case, it is simply impossible not to know about your disease, because it cannot occur without serious consequences. Information that the window period can be affected by drug use is not true.

To finally close the topic of ELISA tests, I would like to add that for a number of reasons (pregnancy, some diseases, etc.) this test can give a false positive result (in about 1% of cases). Therefore, any positive ELISA test is always rechecked with a more sensitive and specific test - immunoblot. A positive immunoblot result after a positive ELISA is 99.9% reliable - this is the maximum accuracy for any medical test. And only after such confirmation is a diagnosis of HIV infection made. If the immunoblot is negative, it means that the first test was false positive, and in fact the person does not have HIV.

So, for everyone who is considering taking an HIV test, I will repeat once again the main point of this post: The final reliability of the HIV test is 3 months after possible infection. Although, in most cases, if infection does occur, the ELISA test will become positive long before the end of this period.

UpDt: In order not to be unfounded, I give as an example a translation of an excerpt from the French recommendations for HIV testing (http://www.has-sante.fr): “In case of a possible risk of HIV infection that occurred less than 3 months before the test test, the recommended testing strategy involves detecting antibodies to HIV... 3 months after a possible risk or 3 months after the end of preventive therapy.... Carrying out an antibody test 6 months after the suspected risk or the end of preventive therapy, which was mandatory , according to the order of the Ministry of Health of the French Republic dated January 18, 1993, canceled according to the Order of the Ministry of Health dated August 1, 2007."

An HIV screening test helps to detect pathology in a timely manner and begin its treatment. Identification of a suspected disease or disorder is carried out through a test that quickly determines the presence or absence of a problem. The 4th generation HIV test helps diagnose pathology in the early stages, when antibodies to the virus have just begun to be released.

Characteristic

The 4th generation HIV test is sensitive to antibodies and p24 antigen. The test system uses a virus that has undergone ultrasonic processing. Antigens are detected 30 days after RNA is determined using the PCR method.

4th generation HIV test systems are useful for doctors one to two months after infection with the virus and are considered the most informative in the early stages of infection. The test has a very high sensitivity to the virus in the initial stages of infection. In some cases, ELISA detects AIDS a week or a week and a half after infection, but the standard period is from two weeks to a month.

The 4th generation HIV test system detects an antigen that is part of the virus and is detected in the blood earlier than antibodies, which require time to form. The conventionally called “window” period or time frame for a 4th generation HIV test is very short. After testing reveals a large number of antibodies against the virus, the p24 antigen no longer appears because it binds to another protein in the blood.

The 4th generation HIV test, the reliability of which is currently considered almost 100%, is often used in the diagnosis of immunodeficiency. To properly complete the study, you must follow the recommendations for preparing for the analysis:

• the study is carried out in the morning;
• blood is donated from a vein;
• Before taking blood, you should not eat anything or take medications.

Time intervals for research

Taking a 4th generation HIV test in a month is considered the best option to get a reliable result. During this period, the amount of p24 protein simultaneously decreases and the level of antibodies produced increases if infection occurs.

It is necessary to take into account various points that influence the result of the study: the state of the patient’s immune system, past infectious diseases, taking potent drugs, and others. In such situations, the study is repeated (several times, taking into account the time frame) as prescribed by the immunologist.

The accuracy of 4th generation HIV tests is due to high sensitivity and specificity. Sensitivity is the number of correctly identified results from known positive samples (infected samples: 100% out of 100). Specificity is the proportion of samples correctly examined by the test that are obviously negative (if there are 10 “supposedly infected results” per 1000 samples of healthy blood, then specificity means 99 percent).

The deadline for taking a 4th generation HIV test after unprotected contact is 3 or 4 weeks (blood is taken from a vein) or 10-12 weeks (from a finger). Resubmit for control after three months, respectively, which is the final inspection period. A repeat examination after 6 months is prescribed by a doctor according to indications.

The fourth generation HIV test detects antibodies to both type 1 and type 2 viruses. It is the most effective diagnostic method in the early period of suspected infection (the most active phase of virus spread occurs). Used for all cases where there was suspected exposure to the virus.

Reviews and comments

Svetlana- 05 Sep 2018, 11:20

Katya, what kind of prevention? Just don't get close to strangers. Take immunostimulating medications. In principle - everything. Well, personal hygiene rules every day.