What is the best time to get tested for Human Immunodeficiency Virus (HIV) after unprotected sex?

HIV Testing Timeline After Unprotected Sexual Exposure

If you had unprotected sex 1 month ago, you should get tested NOW with a laboratory-based fourth-generation antigen/antibody test combined with nucleic acid testing (NAT), and then repeat definitive testing at 12 weeks (3 months) post-exposure to conclusively rule out HIV infection. 1, 2, 3

Optimal Testing Strategy at 1 Month Post-Exposure

At 4-6 weeks (approximately 1 month) after your last unprotected sexual encounter, the CDC recommends:

• Perform both laboratory-based HIV antigen/antibody (Ag/Ab) testing AND diagnostic nucleic acid testing (NAT) at this timepoint 1, 2, 3
• The combination approach is critical because fourth-generation Ag/Ab tests detect HIV infection 18-45 days post-exposure, while NAT can detect infection as early as 10-14 days post-exposure 1, 3
• Laboratory-based tests are significantly more sensitive than rapid point-of-care tests, particularly for detecting recent infections 2, 3

Why Testing at 1 Month Is Important But Not Definitive

• A negative test at 4-6 weeks does NOT rule out HIV infection—you must complete follow-up testing at 12 weeks for a definitive result 1, 2, 3
• The 4-6 week testing serves as an intermediate checkpoint that can identify most infections earlier than waiting until 12 weeks, which is particularly important because persons with acute HIV infection are highly infectious 1, 3
• If you took post-exposure prophylaxis (PEP) within 72 hours of the exposure, antiretroviral medications can suppress viral load and delay antibody formation, potentially affecting test accuracy 2, 3

The Definitive 12-Week Testing Window

• The CDC considers 12 weeks (3 months) post-exposure as the definitive timepoint to conclusively rule out HIV infection when using modern combined Ag/Ab and NAT testing 2, 3
• At 12 weeks, perform both laboratory-based Ag/Ab combination immunoassay AND diagnostic HIV NAT for final confirmation 2, 3
• This 12-week window accounts for antiretroviral washout periods and the maximum window period for modern HIV tests 2, 3

Critical Testing Pitfalls to Avoid

• Never rely on antibody-only tests (including most rapid tests) for recent exposure evaluation, as they will miss acute infection and typically don't detect antibodies until 3-4 weeks after infection 1, 3
• Never use rapid oral fluid tests in the context of potential recent exposure, as they are significantly less sensitive than blood-based laboratory tests 2
• Never stop follow-up testing before 12 weeks, even if your 1-month test is negative 1, 3
• Never delay initial testing while waiting for the "perfect" test—if NAT is unavailable at your facility, proceed with laboratory-based Ag/Ab testing rather than no testing, but ensure NAT is added at 12 weeks 1

Additional Considerations Beyond Testing

• If you did not take PEP within 72 hours of exposure, you should be counseled about pre-exposure prophylaxis (PrEP) for future protection, as you have demonstrated risk behavior 1
• Consider screening for other sexually transmitted infections (STIs) including chlamydia, gonorrhea, and syphilis, as these often co-occur with HIV risk behaviors 4
• If you develop any symptoms suggestive of acute HIV infection (fever, rash, lymphadenopathy) before your scheduled testing, seek immediate evaluation with NAT testing 1, 3