In a patient with suspected acute HIV infection, which laboratory marker becomes detectable in blood earliest after acquisition of infection?

• A Antibodies to HIV detected by rapid third-generation tests
• B HIV p24 antigen
• C Western blot band reactivity
• D Plasma HIV RNA by nucleic acid amplification ✓

Explanation

Plasma HIV RNA is the earliest marker, becoming positive roughly 10 to 12 days after infection, before p24 antigen (about 15 to 20 days) and before antibody (about 3 weeks or later with rapid tests). Western blot confirms antibody positivity latest and was historically responsible for false-negative results in the window period. This sequence explains why nucleic acid testing detects infection during the eclipse-to-viraemia transition when antigen-antibody assays remain negative.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.