Laboratory tests for HIV infection

Laboratory tests for HIV infection

BLOOD TESTS (SEROLOGY). The first blood test for AIDS was developed in 1985. At present, patients who are being tested for HIV infection are usually given an enzyme-linked immunosorbent assay (ELISA) test for the presence of HIV antibody in their blood. Positive ELISA results are then tested with a Western blot or immunofluorescence (IFA) assay for confirmation. The combination of the ELISA and Western blot tests is more than 99.9% accurate in detecting HIV infection within four to eight weeks following exposure. Indeterminate test results are possible (positive ELISA but non-confirmatory Western blot result) if the tests are given within the window period after infection (up to eight weeks after infection, but may be longer). In these indeterminate cases, the ELISA and Western blot should be repeated every three months until a definitive result is made. The patient should be considered HIV positive until proven otherwise. The polymerase chain reaction (PCR) test can be used to detect the presence of viral nucleic acids in the very small number of HIV patients who have false-negative results on the ELISA and Western blot tests.