Serologic testing for human immunodeficiency virus antibodies.

Familiarity with available serologic tests for antibodies to human immunodeficiency virus (HIV) has become increasingly important in a wide variety of clinical settings. Enzyme-linked immunosorbent assay (ELISA) commercial kits are most often used as Enzyme-linked immunosorbent assay (ELISA) commercial kits are most often used as screening tests, and Western blot techniques are used for confirmation of positive results. ELISA specificity and sensitivity exceed 98%; the predictive value of a positive test varies from 2% for a weakly positive test in a low-prevalence population to 99% for a strongly positive test in a high-risk group. Confirmatory Western blot testing identifies antibodies with affinity for specific HIV antigens. Indeterminate Western blot antibody patterns necessitate subsequent testing or alternative methods for interpretation. A "window" period of up to 3 or more months follows acute HIV infection before seropositivity occurs.