HIV infection can be detected in the blood by three tests. These include the HIV Rapid Test (or HIVRT), which is the only test which can be done in a person's home or at a Health Post. The other two tests (the Western blot test and enzyme immunoassay test), can only be done at a higher level health facility. As it is so easy to use, the HIVRT is the most commonly used HIV test in Ethiopia. It involves taking a very small sample of blood from the person's finger by pricking it with a sterile instrument, and taking a drop of blood to place onto a test kit (Figure 16.1). You will learn how to conduct the test and read the result in the Module on Communicable Diseases.
The principle behind all the various HIV testing kits that have been developed to screen blood is the same. The tests are highly sensitive for detecting HIV infection. They work by detecting antibodies (proteins produced by the body to fight infection) which appear in the blood after the window period of HIV infection. The window period is the period of time (up to 12 weeks or 3 months) between the virus entering a person's body and the appearance of detectable antibodies in the person' blood. In some cases, a person with a negative HIV test result may be infected, but the result fails to show up because they are in the window period of infection. Testing this person again after 3 months from the date of infection will usually reveal an HIV — positive result.
A small sample of the person's blood is run through two HIVRT tests using kits from two different manufacturers. Can you suggest why the blood is tested twice using two different testing kits?
It increases confidence in the accuracy of the result if both tests are negative, or if both are positive. If the two results are different, it suggests that a test may not have been carried out correctly and a third test should be conducted as a 'tie breaker'.