Risk factors associated with false positive HIV test results in a low-risk urban obstetric population

Objective. To examine risk factors for false positive HIV enzyme immunoassay (EIA) testing at delivery. Study Design. A review of pregnant women who delivered at Parkland Hospital between 2005 and 2008 was performed. Patients routinely received serum HIV EIA testing at delivery, with positive results confirmed through immunofluorescent testing. Demographics, HIV, hepatitis B surface antigen (HBsAg), and rapid plasma reagin (RPR) results were obtained. Statistical analyses included Pearson's chi-square and Student's t-test. Results. Of 47,794 patients, 47,391 (99) tested negative, 145 (0.3) falsely positive, 172 (0.4) positive, and 86 (0.2) equivocal or missing HIV results. The positive predictive value of EIA was 54.3. Patients with false positive results were more likely nulliparous (43 versus 31, P<0.001) and younger (23.9±5.7 versus 26.2±5.9 years, P<0.001). HIV positive patients were older than false positive patients and more likely positive for HBsAg and RPR. Conclusion. False positive HIV testing at delivery using EIA is associated with young maternal age and nulliparity in this population.