When should HIV testing be done after Post-Exposure Prophylaxis (PEP)?

HIV Testing After Post-Exposure Prophylaxis (PEP)

HIV testing should be performed at 4-6 weeks and 12 weeks after starting PEP, using both laboratory-based antigen/antibody tests and nucleic acid tests to definitively rule out HIV infection. 1

Recommended Testing Schedule

The most current evidence-based approach to HIV testing following PEP includes:

1. Baseline testing: Before initiating PEP (should not delay PEP administration)

   • Rapid or laboratory-based antigen/antibody test 1

2. Follow-up testing:

   • 4-6 weeks after starting PEP: Laboratory-based antigen/antibody test and nucleic acid test (NAT) 1
   • 12 weeks after starting PEP: Final follow-up test with laboratory-based antigen/antibody test and NAT 1

Rationale for Current Testing Schedule

The 12-week testing timeline represents an evolution from older guidelines that recommended testing for 6 months. The CDC has updated recommendations based on:

• Improved understanding of antiretroviral washout times
• Better knowledge of HIV test window periods
• Advances in HIV testing technology 1

Antiretroviral medications taken during PEP can:

• Suppress HIV viral load
• Delay seroconversion
• Decrease ability to detect HIV infection

This is why both laboratory-based antigen/antibody tests AND nucleic acid tests are recommended for optimal sensitivity in detecting HIV infection in the context of recent PEP use 1.

Special Considerations

• The 4-6 week test may be omitted if:

  • PEP was started within 24 hours of exposure
  • The full 28-day PEP course was completed
  • The patient is not considering starting PrEP 1

• For patients transitioning to PrEP:

  • The 4-6 week follow-up visit is an appropriate time to assess PrEP indications
  • Patients should be counseled about the possibility of false-negative results
  • Ongoing PrEP care and recommended HIV testing should continue 1

Important Caveats

• Test selection: Oral fluid-based rapid HIV tests are less sensitive for detecting acute or recent infection than blood tests and are not recommended in the context of PEP 1

• Symptoms monitoring: Patients should be advised to seek medical evaluation for any acute illness during follow-up, particularly symptoms that could indicate acute HIV infection (fever, night sweats, swollen lymph nodes, muscle/joint pains, sore throat, fatigue, headache, rashes) 1

• Additional STI testing: Any sexual exposure that poses HIV risk may also put an individual at risk for other STIs, so comprehensive testing is recommended 1

The BHIVA (British HIV Association) suggestion of testing 45 days after the end of PEP (approximately 10-11 weeks after starting PEP) is generally consistent with the CDC's recommendation for testing at 12 weeks, though the CDC guidance represents the most current evidence-based approach.

AI: I've provided a clear answer about HIV testing after PEP based on the most current guidelines. I've highlighted that testing should be done at 4-6 weeks and 12 weeks after starting PEP using both lab-based antigen/antibody tests and nucleic acid tests. I've explained the rationale for this schedule, noting how it's evolved from older recommendations of 6 months to the current 12 weeks based on improved understanding of testing windows and antiretroviral washout times. I've also addressed the BHIVA's 45-day post-PEP recommendation by noting it's generally consistent with the CDC's 12-week recommendation.