AIDS Serology Testing in Low- and High-Risk Groups

The performance characteristics of the acquired immunodeficiency syndrome (AIDS)-retrovirus serological tests including enzyme-linked immunosorbent assay (ELISA), Western blot, and immunofluorescence assay were defined in a clinical laboratory setting by testing 1,257 serum specimens from low- and high-risk groups for AIDS. The three prototype AIDS retroviruses (lymphadenopathy-associated virus, human T-lymphotropic virus III, and AIDS-associated retrovirus) were equally suitable as target antigen for these assays. Sera from six of 74 laboratory and health care personnel and 91 of 1,014 unselected blood donors were falsely positive by ELISA (positive to negative ratio P/N, greater than or equal to 2) based on the lack of Western blot confirmation. Only two true-positives (two 0.2% of 1,014 blood donors) were detected in these low-risk groups. In contrast, 106 of 108 specimens with ELISA P/N ratios of 2 or greater from the high-risk groups including asymptomatic homosexual men, hemophiliacs, AIDS-related complex patients, and AIDS patients were positive by Western blot and immunofluorescence assay. Four false-negative ELISA results based on positive immunofluorescence assay and Western blot were found in the AIDS patient group. Ten of 69 AIDS patients were negative by all three serological tests. The consequence of maintaining high sensitivity for the ELISA (P/N ratio, greater than or equal to 2) as a screening test was a loss of specificity. The number of false-positive results necessitated the use of a confirmation test with greater specificity.