What is the difference between BHIVA (British HIV Association) and CDC (Centers for Disease Control and Prevention) guidelines for HIV testing after Post-Exposure Prophylaxis (PEP)?

Differences Between BHIVA and CDC Guidelines for HIV Testing After Post-Exposure Prophylaxis (PEP)

The key difference between BHIVA and CDC guidelines for HIV testing after PEP is the timing and type of follow-up testing: CDC recommends HIV testing at 4-6 weeks and 12 weeks after PEP initiation using both laboratory-based antigen/antibody tests and nucleic acid tests, while BHIVA typically recommends testing at 12 weeks post-exposure using a fourth-generation combined antibody/antigen test. 1

Testing Timeline Differences

CDC Recommendations:

• Initial testing: Rapid HIV antibody/antigen test at baseline before starting PEP 1
• First follow-up: Laboratory-based Ag/Ab test AND diagnostic nucleic acid test (NAT) at 4-6 weeks after PEP initiation 1
• Final follow-up: Laboratory-based Ag/Ab test AND diagnostic NAT at 12 weeks after PEP initiation (8 weeks after completion) 1

BHIVA Approach:

• Initial testing: Fourth-generation HIV antigen-antibody test at baseline
• Follow-up testing: Single test at 12 weeks post-exposure using fourth-generation combined antibody/antigen test

Testing Methodology Differences

• CDC: Emphasizes using both laboratory-based Ag/Ab tests AND diagnostic NAT for follow-up testing to improve detection of acute infection 1
• BHIVA: Typically relies on fourth-generation combined antibody/antigen tests without requiring NAT

Rationale for Testing Approaches

CDC Rationale:

• Early testing at 4-6 weeks can identify HIV infections in persons with poor PEP adherence 1
• Dual testing method (Ag/Ab + NAT) accounts for potential delayed seroconversion due to antiretroviral use 1
• NAT can detect acute HIV infection approximately 1 week before laboratory-based Ag/Ab tests 1

BHIVA Rationale:

• Single definitive test at 12 weeks is considered sufficient when using fourth-generation testing
• Simplifies the testing protocol for patients

PrEP Transition Considerations

• CDC: Explicitly addresses transition from PEP to PrEP, stating PrEP can be initiated immediately after PEP completion without a gap, with ongoing HIV testing 1
• BHIVA: Less explicit guidance on PEP-to-PrEP transitions

Special Testing Considerations

• CDC: Recommends additional consideration for persons who have recently taken oral antiretrovirals or had cabotegravir injections 1
• CDC: Explicitly states that oral fluid-based rapid HIV tests are not recommended for screening in the context of PEP due to lower sensitivity for acute infection 1

Common Elements in Both Guidelines

Both guidelines agree on:

• The need for baseline HIV testing before PEP initiation
• The importance of not delaying PEP while waiting for test results
• The recognition that antiretroviral drugs can delay seroconversion and affect test results

Clinical Implications

• Clinicians should be aware that CDC guidelines recommend more frequent testing and more sensitive testing methodologies
• The dual testing approach recommended by CDC (Ag/Ab + NAT) may detect HIV infections earlier but requires more resources
• The timing of PrEP initiation after PEP completion differs between guidelines, with CDC explicitly supporting immediate transition

Pitfalls to Avoid

• Don't rely solely on antibody-only tests for follow-up after PEP, as they may miss acute infections
• Don't assume a negative test at 4-6 weeks definitively rules out HIV infection, as antiretrovirals can delay seroconversion
• Don't create unnecessary gaps between PEP completion and PrEP initiation if ongoing HIV risk exists

Understanding these differences is crucial for healthcare providers to deliver appropriate post-PEP care based on their local guidelines and available resources.