Since nearly all children born to seropositive mothers are HIV antibody-positive, diagnosis relies on the direct detection of HIV genetic information by DNA polymerase chain reaction (PCR), RNA PCR, or by HIV culture or detection of HIV protein p24. Diagnostic testing, usually with a DNA PCR analysis, should be performed between birth and 48 h, 1-2 months of age, and 3-6 months of age. Data suggest that HIV DNA PCR is positive in approximately 38% of the infected children by 48 h, and in 93% of infected infants by the second week. A birth to 48 h sample in some cases may not be obtainable, in which case a schema of phlebotomies beginning at 14 days of age with a repeat at 2-4 months of age provides accurate diagnosis in most cases. The HIV DNA test is now widely available commercially and is accurate. Two positive confirmatory tests establish the diagnosis of HIV, whereas two negative tests rule it out.37 HIV RNA in plasma may also be useful; however, it has not been studied as completely as DNA PCR. HIV culture is more expensive and is probably less sensitive.3839 Cord blood should not be sampled to avoid false positives.
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