Blood-Borne STI Testing Intervals After Exposure
For HIV testing after exposure, perform testing at baseline, 4-6 weeks, and 12 weeks post-exposure using both HIV Ag/Ab and diagnostic NAT tests. 1
HIV Testing Schedule
The 2025 CDC guidelines provide the most current and authoritative testing intervals for HIV post-exposure:
Baseline (initial visit): Rapid point-of-care or laboratory-based HIV Ag/Ab test, plus diagnostic HIV NAT if the exposed person had long-acting injectable PrEP in the past 12 months 1
4-6 weeks post-exposure: Both laboratory-based HIV Ag/Ab test AND diagnostic HIV NAT 1
- Important caveat: This interim testing may be deferred if nPEP was started within 24 hours of exposure and no doses were missed 1
12 weeks (final): Laboratory-based HIV Ag/Ab combination immunoassay AND diagnostic HIV NAT 1
This represents an update from older practices that recommended 6-month testing windows 2. The dual testing approach (Ag/Ab plus NAT) at both interim and final timepoints maximizes diagnostic sensitivity.
Hepatitis B Testing
For hepatitis B, test at baseline and at 6 months post-exposure if the exposed person was HBV non-immune at baseline. 1
- Baseline testing includes HBsAg, HBsAb, and HBcAb 1
- No interim testing is required
- 6-month follow-up only applies to those who were non-immune initially
Hepatitis C Testing
For hepatitis C, baseline testing is recommended, with follow-up testing only if clinically indicated based on risk assessment. 1
- Baseline: HCV antibody testing for the exposed person 1
- Source testing: HCV RNA NAT if indicated 1
- The guidelines do not mandate routine follow-up HCV testing at specific intervals unless the exposure warrants it
Syphilis Testing
For syphilis, test at baseline, 4-6 weeks, and 12 weeks post-exposure. 1
This mirrors the HIV testing schedule and ensures detection during the window period for syphilis seroconversion.
Gonorrhea and Chlamydia Testing
For gonorrhea and chlamydia, test at baseline only using NAAT from appropriate anatomic sites. 1
- No routine follow-up testing intervals are specified in the guidelines
- Testing should be site-specific based on exposure (urogenital, rectal, pharyngeal) 1
Key Clinical Considerations
Common pitfalls to avoid:
- Do not wait for laboratory results before initiating nPEP if indicated—use rapid testing to guide immediate decisions 1
- Do not rely solely on Ag/Ab testing; the addition of diagnostic NAT at 4-6 and 12 weeks is now standard of care 1
- Do not extend HIV testing beyond 12 weeks in typical exposures—the older 6-month window is outdated 2
Special populations:
- Persons with recent long-acting injectable PrEP exposure require diagnostic HIV NAT at baseline in addition to standard Ag/Ab testing 1
- Pregnant individuals require pregnancy testing at baseline and 4-6 weeks 1
The evidence strongly supports this structured approach, with the 2025 CDC guidelines representing the highest quality, most recent guidance available for post-exposure management 1.