In the sequence of laboratory markers after HIV acquisition, which order of first detectability is correct?
- A HIV RNA, then p24 antigen, then antibody ✓
- B Antibody, then p24 antigen, then HIV RNA
- C p24 antigen, then HIV RNA, then antibody
- D All three become detectable simultaneously at seroconversion
Correct answer: A. HIV RNA, then p24 antigen, then antibody
Explanation
Plasma HIV RNA is the earliest marker, detectable by NAAT roughly 10 days after exposure. p24 antigen appears next, around 15 to 20 days, giving the fourth-generation combination assay its shorter window period than antibody-only tests. Antibody becomes detectable by third-generation assays at about 3 weeks. This staggered appearance explains why NAT shortens the transfusion window period the most.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.