Reactive Fourth-Generation HIV Assays at Low Cut-Off Indices May Be Clinically Misleading in the Obstetric Setting: A Multicenter Analysis of 904 Reactive Cases.

OBJECTIVES

False-positive HIV screen tests have clinical and social consequences when time constrains necessitate interventions before confirmatory results are available, such as in late phases of pregnancy. We conducted this study to test the performance of HIV screening in pregnancy and explore ways to address the challenges caused by false positives.

METHODS

Cases with a reactive fourth-generation HIV screening assay were identified, and the cut-off indices (COIs), confirmatory HIV test results, and pregnancy status at the time of testing were acquired through digital archives of two tertiary centers. These data were used to calculate positive predictive value (PPV) with the standard and alternative COI thresholds.

RESULTS

Among 904 reactive screens, 58.6% were false positive. Pregnant women (n = 112) had a markedly lower PPV than the rest (12.5% vs 45.5%, P < 0.0001). COI distribution clusters were distinctly apart between false- and true-positive cases (median 1.9 vs 608.0; P < 0.0001). Two COI thresholds, 1.0 (standard) and 3.0 (explorative), were equally sensitive; however, the PPVs were 41.4% and 70.1%, respectively. COI threshold of 15.9 had the best numeric balance with 99.2% sensitivity and 95.4% PPV.

CONCLUSIONS

Reactive fourth-generation HIV screenings among pregnant woman were mostly false positive in a low-prevalence community. This study found alternative COI thresholds to improve PPV without significantly jeopardizing sensitivity.