Question
Window period in HIV infection
Answer
The window period in HIV infection is the interval between actual infection and the time a given diagnostic test becomes capable of reliably detecting it — during this period, the individual is infected and potentially infectious, but standard testing may give a false-negative result.
Basis: viral markers appear in sequence — HIV RNA (earliest, ~7–10 days, PCR/NAT), then p24 antigen (~2–3 weeks), then HIV antibody (~3–12 weeks) — a test relying only on a later-appearing marker has a correspondingly longer window period.
Significance: critically important for blood/organ donor screening (a recently-infected donor could test falsely negative yet still transmit HIV); individuals tested soon after a suspected exposure should repeat testing after an appropriate interval.
Narrowing the window: 4th-generation combination antigen/antibody assays (detecting both p24 antigen and antibody) — now the recommended standard — have shortened the window period to approximately 2–3 weeks, compared to ~3 months for older 1st/2nd-generation antibody-only assays.