A neonate born to an HIV-positive mother is tested at 6 weeks of age. The HIV antibody ELISA is reactive. What is the recommended diagnostic approach to confirm or exclude HIV infection in this infant?
- A Repeat HIV antibody ELISA at 3 months — if still reactive, confirm infection
- B HIV-1 DNA PCR (or HIV-1 RNA PCR) — virological test, because maternal IgG antibodies cross the placenta and may persist up to 18 months ✓
- C p24 antigen assay — p24 is the most sensitive test in neonates under 6 weeks
- D Western blot — it differentiates maternal from neonatal antibody bands
Correct answer: B. HIV-1 DNA PCR (or HIV-1 RNA PCR) — virological test, because maternal IgG antibodies cross the placenta and may persist up to 18 months
Explanation
Maternal IgG anti-HIV antibodies passively cross the placenta and persist in the infant for up to 12–18 months, making serology (ELISA, Western blot) unreliable for neonatal diagnosis. HIV-1 DNA PCR (early infant diagnosis, EID) or RNA PCR is the virological assay of choice from 6 weeks of age; a positive result indicates true infection. p24 antigen has lower sensitivity in early infancy. Western blot reflects antibody (maternal or infant) and cannot differentiate the source.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.