For how long after exposure to a patient with HIV should an individual repeat testing to confirm a negative result?

HIV Testing Timeline After Exposure

After exposure to HIV, perform final HIV testing at 12 weeks (3 months) post-exposure using both laboratory-based antigen/antibody combination immunoassay and diagnostic HIV nucleic acid test (NAT) to definitively confirm negative status. 1

Testing Schedule Algorithm

Baseline Testing (Immediately After Exposure)

• Perform rapid or laboratory-based antigen/antibody (Ag/Ab) combination HIV test at initial evaluation 1
• If the exposed person has had long-acting injectable PrEP in the past 12 months, add diagnostic HIV NAT testing at baseline 1

Interim Testing (4-6 Weeks Post-Exposure)

• Perform both laboratory-based HIV Ag/Ab test plus diagnostic HIV NAT test at 4-6 weeks after exposure 1
• Important caveat: This interim testing may be deferred only if the person started post-exposure prophylaxis (PEP) within 24 hours of exposure and did not miss any doses 1

Final Testing (12 Weeks Post-Exposure)

• Perform final HIV tests at 12 weeks (3 months) after exposure using both laboratory-based HIV Ag/Ab combination immunoassay and diagnostic HIV NAT 1
• This represents the definitive timepoint to confirm negative status with current testing methods 1

Key Differences from Older Guidelines

The 2025 CDC guidelines represent an important update from previous recommendations:

• Older guidelines recommended testing for at least 6 months post-exposure using traditional antibody-only tests 1, 2
• Newer fourth-generation testing (combination Ag/Ab plus NAT) allows for conclusive testing at 4 months instead of 6 months 3
• Current 2025 guidelines further refine this to 12 weeks (3 months) when using both Ag/Ab and NAT testing together 1

Clinical Context and Rationale

Why 12 Weeks Is Sufficient

• The body typically produces detectable HIV antibodies within 4-6 weeks after infection 2
• HIV antibody is detectable in ≥95% of patients within 6 months using traditional tests 2
• Modern combination Ag/Ab tests detect both HIV antibodies and p24 antigen, shortening the window period 3
• Adding diagnostic NAT testing further increases early detection capability 1

Important Caveats

• Rare instances of delayed seroconversion beyond 6 months have been documented, though these are exceptional cases 2
• If the exposed person develops any illness compatible with acute retroviral syndrome at any time, perform HIV testing immediately regardless of the interval since exposure 1
• Approximately 81% of healthcare workers with documented seroconversion experienced acute retroviral syndrome at a median of 25 days after exposure 2

Extended Follow-Up Considerations

Extended follow-up to 6 months may be warranted in specific circumstances:

• If the person becomes infected with hepatitis C virus (HCV) following exposure to a source coinfected with HIV and HCV 1
• If newer fourth-generation testing platforms are not available, revert to 6-month follow-up 3
• Individual clinical judgment may dictate extended follow-up in complex cases 1

Post-Exposure Prophylaxis Context

If PEP is indicated and initiated:

• Start within 72 hours of exposure (ideally within 2 hours) 1, 4
• Continue for 28 days 1
• The testing schedule remains the same regardless of PEP use, though interim testing at 4-6 weeks may be deferred if PEP was started within 24 hours and adherence was perfect 1