According to WHO statistics, over the past 40 years, 25 million people have died from AIDS. The damage from this infection is colossal. The most infected were in African countries, where this infection came from. With HIV, the diagnosis of the disease becomes especially relevant. True, the means for treating HIV has not yet been created, but early treatment can extend the patient's life and improve its quality.
Diagnosis of HIV infection
HIV infection is determined at different stages by the following methods:
- ELISA - enzyme immunoassay.
- Western blot.
- PCR - polymerase chain reaction.
- Rapid tests.
The PCR method was developed by the American biochemist Cary Mullis, who received the Nobel Prize for this in 1983. Today, this method in medicine in the diagnosis of all infections is considered to be leading due to its accuracy and information content. HIV in this regard is no exception.
The essence of the analysis
Any living cell contains RNA and DNA. These nucleic acids are capable of self-copying and self-reproduction. For each infection, DNA fragments are unique. In biological fluids, these nucleic acid fragments circulate. They are captured and recognized by special equipment - a reactor. This is the basis of the method. The laboratory assistant counts these fragments. In HIV retrovirus, RNA is monitored. Even with single copies of viral particles, PCR can detect and count them.
Venous blood is most often used as the test fluid. Special components of the method come into contact with the particles of the virus and make them detectable, because there is a multiple increase in the found fragments.
In the case of HIV, the result of the virus can be obtained long before the clinic appears. Therefore, due to its high sensitivity, PCR has such a high diagnostic value. A huge plus of PCR is the versatility of the method. The incubation period of infection for PCR is not an obstacle.
Research cost
The PCR method is quite expensive. This is one of its big disadvantages. For its implementation, the latest equipment and high qualification of a laboratory doctor are needed. In view of the above, PCR diagnostics are not performed in small settlements. Analysis can be submitted only in specialized large clinics.
The cost of determining HIV DNA in clinics in Moscow is from 2,800 rubles, the determination of the viral load (virus RNA in plasma) by PCR is from 8,800 rubles, and HIV resistance to protease inhibitors is from 16,500 rubles. As you can see, the prices are quite high. PCR can be performed free of charge in state polyclinics under the compulsory medical insurance policy. It is important that the procedure can be done anonymously. In the registry, the patient receives a number by which he can find out the result. In modern medical centers there are personal accounts of clients where these data will be entered.
Study objectives
PCR diagnostics for HIV is prescribed in such cases:
- Detection of infection in a child born to a sick mother or carrier to determine intrauterine infection.
- If ELISA gives dubious results (PCR for HIV helps in this case make a final diagnosis).
- To identify the quantitative content of the virus in the body.
- With positive immunoblotting, they complement each other with PCR.
- Donor testing.
- For early diagnosis of HIV.
- To determine the effectiveness and resistance to ART.
The advantage of this analysis is that PCR for HIV can be performed even for children up to a year old.
The study is more often performed not for the initial diagnosis, but already in the course of treatment. The primary diagnosis is serological studies (they determine the level of antibodies to HIV). With a false-positive result, it is repeated - this can be with a low viral load.
PCR diagnoses HIV when there are no antibodies to it yet. The ELISA method in this case will not give an answer.
And PCR for HIV will already be positive. But the symptoms of this period of HIV are nonspecific. The patient is first treated for a long time and unsuccessfully for ARVI by a therapist. It should be borne in mind that the diagnosis of HIV only on the basis of PCR is not made, it is necessary to undergo other complex tests. The PCR method is often auxiliary to complex cases.
Analysis preparation
Before passing the PCR for HIV, 2 days before the analysis, you should not eat fatty foods, alcohol. It is also better not to strain mentally and physically. If the patient is prescribed a course of immunostimulation, it is stopped 2 weeks before the analysis.
It is better to donate blood in the morning. Other body fluids (semen, vaginal secretions) can also be examined, but the best material is blood. Saliva, sweat, urine and tears are not used, since the virus content in them is minimal.
Benefits of PCR for HIV
The advantages of the method are the extremely low probability of a false positive result, the universality of the reaction for any biological body fluids. The analysis has a wide range:
- A single blood sampling can be used to detect different infections.
- The technique is urgent, the result is ready the very next day.
- Reliability is from 85 to 98%.
- The presence of HIV can be determined 10-14 days after infection (there are no antibodies at this time).
- There are no age restrictions, it can be carried out immediately from the moment of birth.
Cons of the method
The disadvantages of PCR are as follows:
- The high cost of analysis.
- Complex medical equipment is needed.
- Highly qualified laboratory assistant and doctor taking the analysis.
- The reaction is highly sensitive, so the error can be 20%.
- A false-positive result can be obtained if the patient has autoimmune processes, oncology, chronic infections.
- Special cleanliness of the laboratory premises is necessary, because the virus can get into the analysis from the air. Then the result will be wrong.
For laboratories in which PCR is carried out, in order to improve the quality of diagnostics, special strict measures have been developed for the SanPiN system for internal control. In addition, all operating rules must be followed with this technique:
- It is required to strictly follow the information on the test tubes.
- Before blood sampling, look again and make sure the appointment of the analysis.
- The nurse must correctly label the tubes.
- The laboratory doctor must correctly carry out all manipulations with the biomaterial in order to prevent cross-contamination.
- The test system must be of excellent quality.
Only if all these conditions are met, the error in the answer can be only about 2% of episodes.
Analysis duration
Many people wonder how much PCR for HIV will be ready. Diagnosis lasts no more than 8 hours. The patient can get an answer the next day. Rapid testing is performed within 2 hours.
PCR Reliability
Despite its many advantages, PCR is not considered an ideal diagnostic method. He is contacted if necessary to obtain screening tests for the presence of HIV in the body.
When is blood taken for analysis?
How long should I get PCR for HIV? A reliable result can be obtained already by taking blood 4-4 days after the alleged infection. After 2 weeks, HIV confidence will be 98%, and for 5 days, 80%. The presence of a negative result in PCR for HIV will be reliable, but ELISA is also performed for an absolutely accurate result.
ELISA analysis will be effective only in the presence of antibodies to the virus, this time can take from 1-3 months to six months. Since ELISA gives a higher probability (98% -99.9%), PCR cannot be called a 100% confirmatory test for the presence of HIV infection. But then this is the only technique in which you do not need to wait for the appearance of antibodies.
In case of HIV by PCR, one can obtain information on the effectiveness of ART, the stage of HIV disease and the number of VL (quantitative assessment of the presence of HIV in the body). This will indicate the severity and extent of the changes.
PCR tests for HIV should also be done if there are antibodies in the blood, but their presence does not indicate the reliability of the HIV infection clinically.
They give an analysis not only with infection and casual sexual intercourse. Other reasons:
- Pregnancy planning.
- Upcoming operation.
- Random sexual intercourse.
- Some professions require passing this analysis for admission to work (teachers, doctors and other medical personnel).
- Prisoners.
- TB patients.
- EMERCOM and police officers.
- Returned after vacation from exotic countries (if you want to make sure that there is no infection).
- Prostitutes.
- Foreign students.
- Drug addicts.
Also, a certain symptomatology in a patient may force an HIV test:
- Sudden weight loss.
- Diarrhea lasting more than 3 weeks.
- Unreasonable increase in temperature for a long time.
- Enlarged lymph nodes.
- The unexplained cause of pneumonia, candidiasis, etc.
Decryption of the analysis is the prerogative of the attending physician, not the laboratory assistant.
PCR or ELISA, which is better?
During PCR diagnosis of HIV, the RNA of the virus is detected both qualitatively and quantitatively. This analysis clearly identifies the specific pathogen, even if several cross-reacting ones are present. Biological material can be used even in dried form. The minus is the high sensitivity of PCR, when a false-positive result can give the presence on the instruments or test tube even a tiny amount of extraneous DNA.
The task and the possibility of ELISA is to determine the presence of antibodies to retrovirus. Although its accuracy is 99%, in the early stages it is not applicable.
Qualitative HIV Testing
Conducting quality PCR for HIV determines the presence of the virus in the body. The results in this case will look as follows: positive, false positive, negative. But this study will not provide information on the amount of retrovirus. Such a qualitative analysis is inappropriate when HIV has already been detected in the body in other ways.
It is impossible to control the effectiveness of treatment with high-quality PCR.
HIV quantification
Already carried out only by HIV-infected in order to count the number of copies of the RNA of the virus in the biological product.
The purpose of this study is to monitor the treatment and identify the resistance of the virus to it. Antiviral therapy in such calculations is not blindly prescribed by a doctor, therefore, it will be more effective. Quantitative PCR for HIV infection is done much more often. This analysis displays a copy / ml of blood.
What results can be issued:
- The virus RNA is absent or very small (about 20 copies / ml). There is no reliable diagnosis.
- From 20 to 10 to the 6th degree of copies / ml - the diagnosis is reliable.
- More than 10 to the 6th degree of copy / ml is a large BH.
Laboratories can perform real-time PCR analysis for HIV. This implies the observation and numerical assessment of the accumulation of PCR products with automatic recording of results.