When rapid quantitative or qualitative HIV RNA assays are not available in an acute care setting, an ARCHITECT HIV Ag/Ab assay signal-to-cutoff (S/Co) ratio <5 and nonreactive differentiation assay can provide sufficient evidence in low-risk pregnant women to justify deferring unnecessary intrapartum interventions, according to new results published in the American Journal of Obstetrics and Gynecology.

False-positive HIV screening tests in pregnant women can lead to unnecessary interventions when the women go into labor, but a reactive screen requires a differentiation assay, and supplemental qualitative RNA testing is also needed for nonreactive differentiation assay. The ARCHITECT Ag/Ab Combo assay has demonstrated 100% sensitivity and >99% specificity in individuals who are not pregnant, but its performance in pregnancy is yet unclear. In this study, the authors conducted a retrospective review of the diagnostic accuracy of the ARCHITECT HIV Ag/Ab Combo assay in a pregnant cohort that included 21,163 women who were screened using the ARCHITECT assay. Of this group, 190 women tested positive.

The results showed a sensitivity of 100% (95% CI, 97.7%-100%), a specificity of 99.8% (95%CI, 99.8%-99.9%), a positive likelihood ratio of 636 (95% CI, 453-895), a negative likelihood ratio of 0.0 (95% CI, NA), a positive predictive value of 83% (95% CI, 77%-88%), and a false-positive rate of 0.16% (95% CI, 0.11%-0.22%). The women who received false-positive results tended to be younger and more likely to be of Hispanic ethnicity.

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“[W]ithout the availability of rapid HIV RNA assays on Labor and Delivery, the ARCHITECT S/Co ratio could be a useful adjunctive tool to guide intrapartum and neonatal management for low risk pregnant women without symptoms or risk factors for acute HIV infection, while awaiting confirmatory RNA assay results,” write the authors.

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Adhikari EH, Macias D, Gaffney D, et al. Diagnostic accuracy of 4th generation ARCHITECT HIV Ag/Ab combo assay and utility of signal-to-cutoff ratio to predict false positive HIV tests in pregnancy [published online June 15, 2018]. Am J Obstet Gynecol. doi: 10.1016/j.ajog.2018.06.008.