Human immunodeficiency virus (HIV) infects and destroys lymphocytes, the major component of immune system that fights back all infections of the body. Hence, the immune system gets weakened and immune-compromised persons are at very high risk of catching other infections and diseases.
It could further lead to the disease referred as Acquired Immunodeficiency syndrome or AIDS. Medical communities have developed medications to interfere in HIV growth and delay its progression into AIDS.
Different Tests For AIDS Detection
Enzyme Linked Immunosorbent Assay (ELISA)
HIV ELISA is the most renowned test performed for detecting HIV antibodies within the body. These antibodies are being formed by the immune system as first signal in response to HIV infection. But these antibodies take four to six weeks to appear in the blood, hence, the test comes positive after gap of around six weeks (or longer in few cases) of infection.
This test has to be necessarily performed to confirm the infection, even if the disease is detected by more advanced methods of PCR testing. ELISA test is easy to perform using small amount of blood sample but normally takes a day or more to get reported.
There are chances of false positive (when infection is not there) results in ELISA; hence, it should also be confirmed using another testing methodology.
HIV Rapid Tests
Rapid tests are fast and easy to perform without requirement of any instrumentation and hence, can be done at any place, even bedside of the patient. It is done by using a drop of blood from pricked finger and results appear within 15 minutes. They come as an easy solution for screening of large population, especially in rural regions.
These are comparatively cheap and produce highly reliable results that can be as good as that of ELISA. Only consideration is that these rapid kits need to be transported under recommended temperatures and conditions, to keep them effective for producing correct results.
CD4 Count (lymphocytes count)
HIV infects lymphocytes, particularly CD4 positive cells of the body. As virus multiplies in infected cells, virus copies increases that inturn kills more and more of CD4 positive cells.
Therefore, by measuring CD4 positive cells and getting CD4 ratio with respect to CD 8 cells (unaffected cells), doctors can provide analysis of HIV progression and the effectiveness of HIV therapy for patients under treatment. CD4 cell count and CD4 to CD8 ratio is performed using an instrument, flow cytometry.
The normal count of CD4 positive cells should be within 600 -1200 cells per cubic mm of blood. Tremendous fall of the cell count refers to cause of serious concern. When CD4 counts fall below 200 cells, HIV patient is known to be progressing towards AIDS.
ELISA based tests measure the responsiveness of body to infections and takes longer time. Instead, viral tests enable one to detect viral particles directly either by detecting its antigen (present on viral surface) or by detecting the actual viral copies present to predict the progression of HIV to AIDS. These tests are expensive and not available at all places.
p 24 Antigen Testing
The protein p24 is the core protein of HIV virus. Since, antibody takes long duration to appear in the blood, p24 antigen testing is employed as it is capable of detecting the virus one week before antibody production.
This test is also performed similar to antibody testing and may have chances of false negative (when actually it may be positive) results. It is usually done in early stages of HIV infection and in final phases of AIDS and therefore, useful for detection of HIV infection in babies. It is much less sensitive than PCR based testing.
Testing of HIV infection using PCR technology enables one to get the diseased status within few hours, and is highly sensitive test that is free from false negative results, unlike ELISA. Person with HIV symptoms, but negative HIV antibody test, should necessarily have this test to confirm and cross check the presence of virus particle inside the blood. PCR detects the genetic material of the virus in the blood. PCR is very accurate and useful to diagnose early HIV infection.
The available PCR tests are capable of detecting even a single copy of virus present in the bloodstream. The further advancement has occurred, with real time PCR that even quantifies the exact copies of virus present, known as viral load test.
The viral load testing is a reliable indicator of prognosis of HIV and AIDS in an infected individual. Additionally, responsiveness of patients to antiretroviral therapy can be very well demonstrated in this testing enabling physician to continue or stop the treatment further.
Drug Resistance Testing
The widespread of HIV disease has developed a few resistant strains of HIV as part of evolution. In order to test, whether the strain of HIV present is resistant to anti HIV medications, drug resistance testing is performed. This helps to prescribe right treatment to patients.
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