Status of current clinical tests for human immunodeficiency virus (HIV): applications and limitations

Two laboratory tests are currently used to detect the human immunodeficiency virus (HIV) specific antibodies that are produced when an individual has been infected by the virus at some time. These include the enzyme-linked immunosorbent assay (ELISA) as the screening test and the Western blot (WB) as the confirmatory test. They are not yet optimally effective and have brought with them some problems, especially when used to screen low risk populations such as asymptomatic blood donors. Currently licensed ELISA tests used to detect HIV have sensitivities that range between 93 percent and 99 percent, and all have specificities greater than 99 percent. An important concern is that the positive predictive value for the ELISA screening test is low in spite of the fairly high sensitivity and high specificity values. This poor predictive value is due to the low prevalence of individuals in the general population who have been infected with HIV. Multiple causes of false positive ELISA and Western blot tests have been identified. They can be eliminated by utilizing reagent antigens which are produced by recombinant deoxyribonucleic acid (DNA). The false negative ELISA and Western blot tests can be reduced by tests designed to detect IgM antibodies to HIV.