How long after exposure to Human Immunodeficiency Virus (HIV) can you confirm you are clear of the infection?

HIV Testing Timeline After Exposure

You can definitively confirm you are clear of HIV infection at 12 weeks (3 months) after exposure when using modern fourth-generation laboratory-based antigen/antibody tests combined with nucleic acid testing (NAT). 1, 2

Modern Testing Timeline

The CDC recommends a structured testing approach using fourth-generation tests that detect both HIV antibodies and p24 antigen, which significantly shortens the window period compared to older antibody-only tests:

Baseline Testing (Immediately After Exposure)

• Perform a laboratory-based antigen/antibody (Ag/Ab) combination test immediately to establish your HIV-negative status before starting any post-exposure prophylaxis (PEP) 1, 2
• If you've used long-acting injectable PrEP in the past 12 months, add an HIV NAT at baseline because antiretrovirals can suppress viral detection 2

4-6 Week Testing

• Perform both laboratory-based Ag/Ab testing AND diagnostic HIV NAT at 4-6 weeks post-exposure 1, 2
• Critical caveat: If you took PEP medications, this testing should occur 4-6 weeks after completing the full PEP course, not from the initial exposure date, because antiretrovirals can suppress viral load and delay antibody formation 1, 2
• A negative test at this point does NOT rule out infection if you took PEP, as medications may suppress HIV detection for longer than 2 weeks after stopping 1

12 Week Testing (Definitive)

• Perform both laboratory-based Ag/Ab testing AND diagnostic HIV NAT at 12 weeks post-exposure—this is your definitive "all clear" timepoint 1, 2
• This 12-week window accounts for antiretroviral medication washout and the complete window period for modern HIV tests 1
• The CDC explicitly states this combined testing at 12 weeks definitively rules out HIV infection in the modern testing era 2

Understanding Detection Windows

Modern fourth-generation tests have dramatically shortened detection times compared to older methods:

• HIV NAT (nucleic acid test): Detects infection approximately 10-14 days post-exposure 2, 3
• Fourth-generation Ag/Ab tests: Detect infection approximately 18-45 days (roughly 2.5-6.5 weeks) post-exposure 1, 2
• Older antibody-only tests: Required 3-12 weeks or longer for detection 3

Critical Pitfalls to Avoid

Don't Use Rapid Tests Alone

• Never rely on rapid point-of-care antibody tests as your sole testing method, especially during the window period 2
• Rapid tests based on oral fluids are specifically NOT recommended in post-exposure situations because they are less sensitive for detecting acute or recent infection 1
• If a rapid test is used initially, always obtain a laboratory-based Ag/Ab test simultaneously 1, 2

Don't Stop Testing Early

• Never stop follow-up testing before 12 weeks when using modern Ag/Ab and NAT testing 2
• Some older guidelines recommended 6-month follow-up with older antibody tests 4, but with fourth-generation tests, 12 weeks is the definitive timepoint 1, 2

Account for Antiretroviral Medications

• If you took PEP or PrEP, antiretrovirals can suppress viral load and delay antibody formation, reducing the ability to detect HIV infection 1, 3
• The 12-week testing window specifically accounts for this antiretroviral washout period 1

Alternative Testing Scenarios

If NAT is unavailable: Laboratory-based Ag/Ab testing alone at 12 weeks post-exposure should detect the vast majority of infections when accounting for antiretroviral washout, though there will be a diagnostic gap where highly infectious individuals may go undetected earlier 1

Swedish guidelines variation: Sweden recommends 6 weeks for HIV-1 with laboratory-based combination tests (or 8 weeks with rapid tests), but 12 weeks for HIV-2 5. However, the CDC's 12-week recommendation with combined Ag/Ab and NAT testing remains the most conservative and definitive approach 1, 2.

Testing Strategy Summary

Use laboratory-based fourth-generation Ag/Ab combination tests, not rapid antibody-only tests, and always include diagnostic HIV NAT at both 4-6 weeks and 12 weeks for optimal sensitivity 1, 2. The 12-week timepoint with this combined testing approach is when you can definitively confirm you are clear of HIV infection 1, 2.