Performance of an alternative laboratory-based algorithm for HIV diagnosis in a high-risk population.

BACKGROUND

An immunoassay (IA) followed by Western blot (WB) or immunofluorescence assay has been the primary algorithm used to provide laboratory confirmation of the diagnosis of HIV infection in the US for more than 20 years. Recently, an alternative diagnostic algorithm was proposed to more accurately identify early HIV-1 infection and differentiate between HIV-1 and HIV-2 infection.

OBJECTIVES

Evaluate a sequential alternative algorithm in which reactive IAs are followed by a rapid HIV test and, if negative, a nucleic acid amplification test (NAAT).

STUDY DESIGN

Specimens from high-risk persons were tested with 4 HIV IAs, 6 rapid HIV tests and NAAT (APTIMA(®)), which are approved by the United States Food and Drug Administration. IAs were repeated in duplicate if specimen volumes were sufficient. The performance of the alternative algorithm was compared to HIV WB and NAAT.

RESULTS

The original study classified 377 specimens as HIV-positive and 3070 as HIV-negative. All 4 IAs correctly identified >99.5% of HIV-positive specimens and, on initial screening, >95.8% of HIV-negative specimens. When repeated, specificity of IAs improved to >99%. Between 6.7% and 12.4% of IA-repeatedly reactive specimens required APTIMA for resolution. The alternative algorithm led to the correct classification of all IA-reactive specimens.

CONCLUSIONS

Regardless of screening IA and rapid test used, the alternative algorithm correctly classified the infection status of all persons with reactive screening IA results. Few specimens required NAAT for resolution, and the proportion requiring NAAT was lower when repeat IA test results were considered.