The 4th generation reagents simultaneously test the presence of antibodies (IgG & IgM) against HIV-1, HIV-2, HIV-0 subtype and the presence of the virus p24 Antigen. This combination results in a reduction of approximately 7 days in the "seroconversion window" that was present in the 3rd generation reagents.
Acquired Immune Deficiency Syndrome (AIDS)
AIDS (Acquired Immunodeficiency Syndrome) is caused by Human Immunodeficiency Virus (HIV), a Retrovirus family virus that can reproduce and infect other cells, even when antibodies against it are present. There are two types of Human Immunodeficiency Virus, type 1 and type 2. HIV-1 is the most common type in the US and Europe, while HIV-2 is mostly confined to West African countries. Serological testing identifies antibodies developed as a result of HIV-1 or HIV-2 infection. There are various strains of HIV and they all attack a subset of T cells known as "helper" T cells, cells that are important in cellular immunity. AIDS induces immunosuppression and susceptibility to infections with opportunistic microorganisms such as Pneumocystis carinii, Candida albicans, Cryptococcus neoformans, Mycobacterium, Toxoplasma gondii, Cryptosporidium and herpes simplex viruses. The most important ways of transmitting HIV are the direct contact between the blood of an uninfected person with the blood of an infected person and transmission during sexual intercourse. Thus, people at high risk for AIDS include sexually active homosexuals, people with multiple sexual partners, needle-sharing intravenous drug users, patients who have received multiple blood transfusions (eg, haemophilia) and newborns of infected mothers. The incubation period can start from 6 days up to several years.
A person may have been infected with the Human Immunodeficiency Virus for many years without showing any symptoms when the virus is in the non-replicating latency period. When the virus begins actively replicating, the patient may develop AIDS. At 2-6 weeks after infection, patients may develop disease with symptoms such as fever, sweating, fatigue, malaise, lymphadenopathy, sore throat and sometimes splenomegaly. Patients may remain asymptomatic for months to years, depending on the course of the disease.
Laboratory tests for HIV
Molecular viral tests detect HIV-specific RNA. Molecular tests can detect HIV infection in the first days after infection. Serological tests (HIV antibodies) can detect HIV infection only after about 3 weeks (for 3rd generation reagents). This 3-week period is called a «seroconversion window»
Many different tests are available to detect HIV. The most common test is screening for antibodies by an immunoenzymatic technique or immunochemioluminescence. These tests are used as screening tests for HIV, but confirmatory tests are needed. Immunoassay techniques detect antibodies against HIV and will therefore give a positive result when antibodies have time to form. If the immunological test is positive, the test is repeated using the same blood sample. If the test is positive again, then the Western blot method is used as the confirmatory method, in which electrophoresis techniques have been used to separate HIV proteins, thereby enabling, with very high specificity and sensitivity, the detection of antibodies against the virus. If the confirmation test is positive, the patient is considered to have serological evidence of HIV infection. It is important to note that serological evidence means exposure to the virus and that the virus is present in the body, but this does not necessarily mean the appearance of clinical manifestations of AIDS.
Studies show that the incidence of false-positive results in a low prevalence population with both immunological techniques and Western blot is approximately 0.0007% and the incidence of false negative results in a population with a high prevalence of the disease is approximately 0.3%. The most common cause of false-negative results is the fact that the laboratory tests are performed at a time between infection and seroconversion before the antibodies are raised, a period that rarely lasts more than 3 months. The use of 4th generation reagents reduces these false negative results by 80 - 90%.
Detection of p24 Antigen (or P24 Peptide, HIV P24 Nuclear Antigen) can be positive for 1-2 weeks and up to about 1 month after infection with the virus. Antigen p24 is detectable during acute (initial) infection, undetectable as the virus becomes latent and detectable again when the infection progresses. Quantitative testing of HIV p24 Antigen is an alternative indicator of disease progression. It should be noted, however, that the antigen usually disappears from the blood during the asymptomatic phase. The p24 Antigen assay can be used to evaluate antiviral therapy as well as to differentiate active neonatal HIV infection from the passive passage of HIV antibodies from the mother's blood. It is also used to detect HIV infection before antibody production (seroconversion), to detect HIV in blood donors, and to monitor antiretroviral therapy.
From 1-6-2017, Diagnostiki Athinon stopped testing for p24 Antigen, as it is now included in the standard testing of HIV antibodies with the 4th generation reagents.
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. Correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.