Immune complex-dissociated p24 antigen in congenital or perinatal HIV infection: role in the diagnosis and assessment of risk of infection in infants.

Immune complex-dissociated (ICD) HIV-1 p24 antigen assay is a rapid technique for assessing the presence of HIV gag or core protein in plasma or serum. In this study, ICD p24 antigen detection in HIV-1 infected mothers and their infants enrolled in the Women and Infants Transmission Study (WITS) was evaluated primarily as a diagnostic assay for HIV-1 detection in young infants and for its association with perinatal transmission. Plasma from 47 infected infants and 160 uninfected infants was examined, along with plasma from 197 of their mothers who had a delivery or close-to-delivery specimen. ICD p24 antigen was detected in plasma of 27.3% of infected infants at birth and in 70% to 81% at 1 to 6 months. The diagnostic specificity at birth was 90% and 98% to 100.0% at 1 to 6 months. The ICD p24 antigen concentration correlated with concurrent quantitative HIV culture results. The risk of transmission from mother to infant was higher if the mother had detectable ICD p24 antigen at or near the time of delivery (p = 0.002), but its presence did not accurately predict transmission (positive predictive value of 36%, negative predictive values of 85%). The relative ease of performing the ICD p24 antigen assay and the low cost compared with that of HIV culture or DNA PCR makes this test a useful adjunct for the diagnosis of perinatal HIV infection and for enhancing understanding of its pathogenesis, particularly where cost and availability limit access to more sensitive assays.