Blood collection on filter paper : A practical approach to sample collection for studies of perinatal HIV transmission

15810 filter paper cards with dried blood spots were collected during a perinatal HIV transmission study in southern Africa to be subjected to polymerase chain reaction (PCR) testing. Infants were seen at ages 6 and 12 weeks with PCR routinely done in duplicate on each sample. Of 186 infants born to HIV-negative mothers two had a single strongly reactive PCR result while the repeated duplicates were both negative. All 24 known positive samples were strongly positive in both tests. Results were available from 1976 duplicate tests on 1235 infants born to HIV-infected women. Based upon the PCR result of a later sample the positive predictive value was 97.6% if both replicates were strongly positive 100% when one of the replicates was strongly positive and 27% when one or both replicates were weakly positive. When both replicates were negative the negative predictive value was greater than or equal to 96.2%. Therefore when a single HIV PCR test has a strongly positive result the infant is very likely infected. A positive PCR result after age 1 month was 98.9% accurate in predicting antibody positivity after 15 months.