HIV Detection and Diagnosis Guidelines

Test-Specific Window Periods

The Centers for Disease Control and Prevention recommends that diagnostic nucleic acid tests (NAT) can detect HIV approximately 10-14 days after exposure, while fourth-generation antigen/antibody (Ag/Ab) tests detect HIV at 18-24 days, and third-generation antibody-only tests require 22-25 days for detection 1
Diagnostic NAT can detect acute HIV infection approximately 1 week before laboratory-based Ag/Ab tests, making it the most sensitive early detection method 1, 2
NAT is particularly important when recent antiretroviral exposure may suppress antibody response, as recommended by the Centers for Disease Control and Prevention 1

The Centers for Disease Control and Prevention recommends using rapid point-of-care or laboratory-based Ag/Ab test at initial encounter, and adding laboratory-based Ag/Ab test if rapid test used initially to increase sensitivity 1
Consider adding HIV NAT for baseline testing if the person recently took oral antiretrovirals or received cabotegravir injection within the past year, as recommended by the Centers for Disease Control and Prevention 1
For individuals NOT on post-exposure prophylaxis, test at 6 weeks, 3 months, and 6 months post-exposure using traditional antibody tests, as recommended by the Centers for Disease Control and Prevention 3, 4
Test immediately if acute retroviral syndrome symptoms develop, regardless of timeline, as recommended by the Centers for Disease Control and Prevention 4

For individuals receiving post-exposure prophylaxis, the first follow-up test should be 4-6 weeks after PEP initiation, using both laboratory-based Ag/Ab test AND diagnostic NAT, as recommended by the Centers for Disease Control and Prevention 1, 2, 5
A negative test does NOT rule out HIV because PEP medications may suppress detection, as noted by the Centers for Disease Control and Prevention 2, 5
The final follow-up test should be 12 weeks after PEP initiation, using both laboratory-based Ag/Ab test AND diagnostic NAT, as recommended by the Centers for Disease Control and Prevention 1, 2, 6
This is the definitive test to rule out HIV infection from the exposure, as recommended by the Centers for Disease Control and Prevention 6

Antiretroviral medications taken as PEP or PrEP can suppress HIV viral load, delay seroconversion, and decrease ability to detect HIV infection, as noted by the Centers for Disease Control and Prevention 1, 2
Oral fluid-based rapid HIV tests are NOT recommended in the PEP context because they are less sensitive for acute or recent infection than blood tests, as recommended by the Centers for Disease Control and Prevention 1, 2
If recommended tests are unavailable, use the most sensitive accessible HIV test, as recommended by the Centers for Disease Control and Prevention 1, 2

When PEP is initiated within 24 hours of a known exposure, the full 28‑day PEP course is completed, and the individual is not concurrently starting pre‑exposure prophylaxis, the 4‑to‑6‑week follow‑up HIV test (both laboratory‑based antigen/antibody assay and diagnostic NAT) may be deferred. This recommendation is based on the 2025 CDC (MMWR Recommendations and Reports) guidance. 7

Retesting after a negative routine HIV screen performed 2 days ago should be guided by the individual’s ongoing HIV risk factors rather than by a fixed interval from the initial test. [8][9]

An asymptomatic screening performed 2 days earlier does not require immediate repeat testing unless the person had a specific high‑risk exposure within the test’s window period. 9

Recommended retesting interval is every 3–5 years. 9
After an isolated higher‑risk event, a one‑time retest at 6–12 weeks post‑exposure is advisable. 9

Routine repeated HIV screening is not necessary. 9
A single screening is sufficient unless the individual’s risk profile changes. 9

When a recent exposure (e.g., partner of unknown status, known HIV‑positive partner, condomless sex with a high‑risk partner) occurs, baseline testing now should be performed using a fourth‑generation antigen/antibody assay, preferably supplemented with HIV‑RNA (NAT) if available. 10