HIV Testing and Prevention After Completing PEP
After completing your 28-day PEP course, you must undergo HIV testing at 4-6 weeks and again at 12 weeks post-exposure using both laboratory-based antigen/antibody tests AND nucleic acid tests (NAT) to definitively rule out HIV infection. 1, 2
Critical Testing Timeline Post-PEP
Your testing schedule depends on when you started PEP and your adherence to the full course:
First Follow-Up Test (4-6 Weeks After Starting PEP)
- Required tests: Laboratory-based HIV antigen/antibody (Ag/Ab) combination test PLUS diagnostic HIV nucleic acid test (NAT) 1, 2
- Purpose: This identifies HIV infection, particularly if you didn't complete the full PEP course or had poor adherence 1
- Important caveat: A negative test at this point does NOT rule out HIV because the antiretrovirals you took can suppress the virus for more than 2 weeks after stopping 1
- This visit is also the appropriate time to discuss starting PrEP if you have ongoing HIV risk 1
Final Definitive Test (12 Weeks After Starting PEP)
- Required tests: Laboratory-based Ag/Ab combination immunoassay AND diagnostic HIV NAT 1, 2
- Purpose: This is the definitive timepoint to rule out HIV infection from your exposure 1, 2
- Timing rationale: This allows for complete antiretroviral washout and accounts for the window period of modern HIV tests 1
- Most laboratory-based Ag/Ab tests will detect HIV acquisition from your original exposure by this time 1
Why Both Tests Are Required
The CDC specifically recommends both test types because:
- HIV NAT detects infection approximately 1 week earlier than Ag/Ab tests (around 10-14 days post-infection versus 18-45 days) 2
- Antiretrovirals taken as PEP can suppress HIV viral load, delay seroconversion, and decrease the ability to detect HIV infection 1
- Using both tests together maximizes sensitivity for detecting HIV at a time when you are highly infectious if infected 1
- Diagnostic NATs are preferred over standard viral load assays because they detect lower levels of HIV 2
Optional Earlier Testing Scenario
You may defer the 4-6 week test ONLY if all of the following apply 1:
- You started PEP within 24 hours of exposure
- You were fully adherent to the complete 28-day course
- You are NOT considering starting PrEP
However, you still MUST complete the final 12-week testing regardless 1.
Extended Follow-Up Situations
You need 12-month extended follow-up (not just 6 months) if 1, 3:
- The source person was coinfected with both HIV and HCV, AND
- You became infected with hepatitis C after the exposure 1, 3
Transitioning to PrEP
If you have ongoing HIV risk, you can start PrEP immediately after completing PEP without waiting for the 12-week test 1. However, you must:
- Be counseled about the possibility of a false-negative HIV test result 1
- Understand the importance of ongoing PrEP care with recommended HIV testing 1
- Complete the 12-week post-PEP HIV testing even after starting PrEP 1
Critical Testing Pitfalls to Avoid
Never rely on rapid antibody-only tests during your follow-up period, as they are less sensitive than laboratory-based tests 1, 2. Oral fluid-based rapid HIV tests are specifically NOT recommended in the PEP context because they miss acute or recent infections 1.
Never stop follow-up testing before 12 weeks when using modern Ag/Ab and NAT testing—this is the definitive timepoint to rule out infection 2.
Never use antibody testing alone if you've recently taken antiretrovirals, as they can delay or suppress antibody development 2.
Immediate Testing If Symptoms Develop
Seek immediate HIV testing if you develop symptoms compatible with acute retroviral syndrome (fever, rash, lymphadenopathy, pharyngitis, myalgias) at ANY time, regardless of your testing schedule 1, 3. Acute HIV infection can present before antibodies are detectable.
Other STI Testing
Since any exposure that warranted PEP also places you at risk for other sexually transmitted infections, you should be tested for other STIs according to CDC STI Treatment Guidelines 1.