2.3. Basic tests
HIV diagnostic methods were developed long ago and are being continuously improved. Currently there are two types of HIV diagnostic tests: indirect tests which allow for identification of antibodies to the virus, which almost 100% of people with HIV have; and direct tests that detect the virus (HIV RNA test) itself and proteins specific to virus.
There are three main phases of HIV infection testing in adults: preliminary, reference and confirmatory.
The most common diagnostic method is the enzymatic immunoassay (ELISA). It is used to identify specific antibodies to HIV, which on average are formed in the period from 3 weeks to 3 months after infection. In modern medicine, the fourth generation ELISA assay is used. This is one of the most sensitive tests, and, according to most experts, it can already be used to confirm or exclude HIV infection after 6 weeks of potential virus exposure.
This preliminary method is very common, especially in anonymous and mass tests.
If the ELISA showed a positive result, then another, more accurate Western blot test should be administered. This test is confirmatory. It has high sensitivity and accuracy. The test allows for detection in human blood of certain antibodies to specific proteins (gp120, gp41, p24, p17, p31, gp36, sgp105, sgp120). The final diagnosis can be made only on the basis of two positive results of ELISA and a Western blot.
If the ELISA test result is positive, in certain cases the HIV test is made twice by using the polymerase chain reaction (PCR), measuring the number of copies of the virus in 1 ml of blood plasma. This test methodology is very sensitive and specific, and is not dependent on the presence of antibodies to HIV and can be used within 10 days after possible viral exposure. PCR is used when you want to get an early preliminary result (before 3 months from time of exposure), or in cases where the immune response may not be a symptom of HIV infection, for example in newborns. This test is a reference point.
All people living with HIV should have blood tests regularly. The most important of them is the determination of CD4 lymphocytes count and viral load level. These analyses show the CD4 lymphocyte count and the number of virus copies contained in 1 µL and 1 ml of blood respectively. The CD4 cell count allows the doctor to evaluate the immune system activity and the viral load provides information about the disease stage and the effectiveness of antiretroviral therapy. The latest methods of treatment can restore the CD4 lymphocyte count to normal values and reduce the viral load to undetectable levels.
According to WHO recommendations, one should start treatment as early as possible, irrespective of viral load and immune status.