Yes, You Need One Final HIV Test at 12 Weeks After Starting PEP
After completing PEP with negative results, you must undergo final HIV testing at 12 weeks post-PEP initiation (8 weeks after completing the 28-day course) to definitively rule out HIV infection. 1
Why Additional Testing Is Required
The antiretroviral medications you took for PEP can suppress HIV viral load, delay antibody formation (seroconversion), and reduce the ability to detect HIV infection even if transmission occurred. 1 This means a negative test during or shortly after PEP does not guarantee you are HIV-negative—the medications may be masking an infection. 1
Required Testing Timeline
Final Testing at 12 Weeks (Most Critical)
- Both a laboratory-based antigen/antibody (Ag/Ab) test AND a diagnostic nucleic acid test (NAT/RNA test) are required at 12 weeks after you started PEP 1, 2
- This timing accounts for antiretroviral medication washout and the window period of HIV tests 1
- This is the definitive test that rules out HIV infection from your exposure 1, 2
Optional Mid-Point Testing at 4-6 Weeks
- Testing at 4-6 weeks after starting PEP (within 2 weeks of completing the course) can be performed but does not rule out HIV infection 1
- A negative result at this time is reassuring but inconclusive because the antiretrovirals may still be suppressing detectable HIV for longer than 2 weeks after stopping 1
- This testing can be deferred if you started PEP within 24 hours of exposure, completed the full 28-day course, and are not considering starting PrEP 1
Why Both Types of Tests Matter
The combination of laboratory Ag/Ab testing plus NAT is critical because: 1
- Laboratory Ag/Ab tests detect HIV approximately 18-45 days after infection 2, 3
- Diagnostic NAT (RNA tests) can detect HIV infection about 1 week earlier than Ag/Ab tests, identifying acute infection when you are highly infectious 1, 3
- Using both tests together maximizes the chance of detecting HIV if PEP failed 1
Important Caveats
If NAT is not available: The 12-week laboratory Ag/Ab test alone should detect the vast majority of infections when accounting for antiretroviral washout, but you will miss the earliest detection window. 2 However, inability to access NAT should not have prevented you from receiving PEP in the first place. 1
PEP failures can occur: Most documented PEP failures are attributed to subsequent exposures that may not be disclosed, not failure of the medications themselves. 1 If you had any additional exposures during or after PEP, inform your provider as this affects interpretation of results.
Avoid oral fluid rapid tests: Do not use oral fluid-based rapid HIV tests for your follow-up, as they are less sensitive for detecting acute or recent infection than blood tests. 1