During HIV infection, a patient has a positive 4th-generation antigen/antibody combo ELISA but negative HIV-1/HIV-2 differentiation assay. HIV RNA PCR returns 85,000 copies/mL. How should this result be interpreted?
- A False positive combo assay — low-risk patient, repeat in 6 weeks
- B Acute HIV infection (window period) — p24 antigen detected before antibody seroconversion ✓
- C Established HIV infection with antibody suppression by antiretrovirals
- D Indeterminate — no clinical significance
Explanation
A positive 4th-generation Ag/Ab combo assay with a negative differentiation assay (which detects HIV-1 and HIV-2 antibodies only) combined with a high viral load is the diagnostic pattern of acute HIV infection during the p24 antigenaemia window period, before sufficient antibody titre has developed for the differentiation assay to yield positive bands. This is a critical diagnostic scenario requiring immediate linkage to care and ART initiation. Repeating the test is inappropriate given the positive RNA PCR. The CDC/WHO algorithm specifies that reactive combo + non-reactive differentiation + detectable RNA = acute HIV-1 infection.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.