According to WHO statistics, over the past 40 years, 25 million people have died from AIDS. The damage from this infection is enormous. Most of the infected turned out to be in Africa, where this infection came from. With HIV, the diagnosis of the disease becomes especially relevant. True, there are no cures for HIV yet, but early treatment can prolong 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 Kary Mullis, who received the Nobel Prize for it in 1983. Today, this method in medicine in the diagnosis of all infections is considered the leading one due to its accuracy and information content. HIV is no exception in this regard.
The essence of the analysis
Any living cell contains RNA and DNA. These nucleic acids are capable of self-copying and self-replication. For each infection, DNA fragments are unique. ATin biological fluids, these fragments of nucleic acids circulate. They are captured and recognized by special equipment - the reactor. This is the basis of the method. The laboratory assistant counts these fragments. The retrovirus HIV is monitored for RNA. Even with single copies of viral particles, PCR can detect and count them.
Venous blood is most often used as the test fluid. The special components of the method contact the virus particles and make them detectable, because the fragments found are multiplied.
In the case of HIV, the result of the presence 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
PCR method is quite expensive. This is one of its big disadvantages. It requires the latest equipment and highly qualified laboratory assistant. In view of the foregoing, PCR diagnostics are not performed in small settlements. You can get tested only in specialized large clinics.
The cost of HIV DNA testing in Moscow clinics starts from 2,800 rubles, viral load (viral RNA in plasma) is determined by PCR - from 8,800 rubles, and HIV resistance to protease inhibitors - from 16,500 rubles. As you can see, the prices are quite high. PCR can be done free of charge in public clinics under the MHI policy. 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.
Research 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 the ELISA gave questionable results (PCR for HIV helps in this case to make a final diagnosis).
- To detect the quantitative content of the virus in the body.
- With a positive immunoblot, they complement each other with PCR.
- Testing donors.
- For early diagnosis of HIV.
- To determine the efficacy and resistance to ART.
The advantage of this analysis is that PCR for HIV can be performed even for children under one year old.
Research is often performed not for primary diagnosis, but already in the process of treatment. Primary diagnostics are serological studies (they determine the level of antibodies to HIV). If a false-positive result is repeated, this may 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 general practitioner. It should be borne in mind that the diagnosis of HIV is only based onPCR is not put, it is necessary to pass other comprehensive tests. The PCR method is more often auxiliary for difficult cases.
Preparing for analysis
Before taking PCR for HIV, 2 days before the test, 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.
Blood is best taken in the morning. Other biological fluids of the body (sperm, vaginal secretion) can also be examined, but blood is the best material. Saliva, sweat, urine and tears are not used, since the content of the virus in them is minimal.
Pluses 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 body fluids. Analysis has a wide range:
- One blood draw can be used to detect different infections.
- The technique is urgent, the result is ready the very next day.
- Confidence is between 85 and 98%.
- The presence of HIV can be determined 10-14 days after infection (there are no antibodies at this time yet).
- No age limit, can be performed immediately from birth.
Cons of the method
The disadvantages of PCR are as follows:
- Cost of analysis.
- Requires sophisticated medical equipment.
- Requires highly qualified laboratory assistant and doctor,taker analysis.
- The reaction is highly sensitive, so the error may be 20%.
- May result in a false positive result 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 that conduct PCR, to improve the quality of diagnostics, special strict measures have been developed according to the SanPiN system for internal control. In addition, all the rules of work with this technique must be observed:
- Required to strictly follow the information on the test tubes.
- Before blood sampling, look again and make sure the analysis is scheduled.
- The nurse must label the tubes correctly.
- The laboratory assistant 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 are interested in how long PCR for HIV will be ready. Diagnosis lasts no more than 8 hours. The patient may receive an answer the very next day. Express testing is performed within 2 hours.
PCR Reliability
Despite its many advantages, PCR is not considered an ideal diagnostic method. He is contacted in casethe need to obtain screening tests for the presence of HIV in the body.
When is blood taken for analysis?
How long to take PCR for HIV? A reliable result can be obtained already when taking blood 4-4 days after the alleged infection. After 2 weeks, the reliability for HIV will be 98%, and with a period of 5 days - 80%. The presence of a negative result in PCR for HIV will be reliable, but for an absolutely accurate result, ELISA is also performed.
ELISA analysis will be effective only if there are 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 on the other hand, this is the only technique in which you do not need to wait for the appearance of antibodies.
With HIV, PCR can provide information about the effectiveness of ART, the stage of HIV disease and the number of VNs (a quantitative assessment of the presence of HIV in the body). This will speak to the severity and extent of the change.
PCR testing for HIV is also necessary if there are antibodies in the blood, but their presence does not indicate the reliability of HIV infection clinically.
They are tested not only for infection and casual sex. Other occasions:
- Planning pregnancy.
- Upcoming operation.
- Casual sex.
- Some professions require this test for admission to work (teachers, doctors and other medical personnel).
- Prisoners.
- TB patients.
- Employees of the Ministry of Emergency Situations and the police.
- Returned from vacation from exotic countries (if you want to make sure that there is no infection).
- Prostitutes.
- Foreign students.
- Drugs.
Also, certain symptoms in a patient may force an HIV test:
- Sudden weight loss.
- Diarrhea lasting more than 3 weeks
- Unreasonable high temperature for a long time.
- Swollen lymph nodes.
- Unexplained cause of pneumonia, candidiasis, etc.
Deciphering the analysis is the prerogative of the attending physician, not the laboratory assistant.
PCR or ELISA, which is better?
When PCR-diagnosis of HIV virus RNA is detected both qualitatively and quantitatively. This analysis clearly identifies a particular pathogen even if there are several cross-reacting ones. Biological material can be used even in dried form. The downside is the high sensitivity of PCR, when a false positive result can be given by the presence of even a tiny amount of foreign DNA on instruments or a test tube.
The task and possibility of ELISA is to determine the presence of antibodies to a retrovirus. Although its accuracy is 99%, it is not applicable in the early stages.
Qualitative HIV testing
Performing high-quality PCR on HIV determines the presence of the virus in the body. The results in this case will look like this: positive, false positive, negative. But this study will not give information about the amount of retrovirus. Such a qualitative analysisinappropriate when HIV infection has already been detected in the body by other means.
It is impossible to control the effectiveness of treatment with high-quality PCR.
HIV quantitation
Performed only by HIV-infected people in order to count the number of copies of virus RNA in a biological product.
The purpose of such a study is to monitor the ongoing treatment and identify the resistance of the virus to it. Antiviral therapy in such calculations is not blindly prescribed by a doctor, so it will be more effective. Quantitative PCR for HIV infection is done much more often. This analysis is displayed as a copy/ml of blood.
What results can be given:
- Virus RNA is absent or very small (about 20 copies/ml). No certainty of diagnosis.
- From 20 - to 10 to the 6th degree copies / ml - the diagnosis is reliable.
- More than 106 copies/ml - high VN.
Laboratories can perform real-time PCR testing for HIV. This implies the observation and numerical evaluation of the accumulation of PCR products with automatic recording of results.
