What laboratory tests are recommended for a patient before initiating Pre-Exposure Prophylaxis (PrEP) with long-acting cabotegravir (cabotegravir)?

Laboratory Testing for PrEP Initiation with Long-Acting Cabotegravir

The best laboratory tests to recommend for T.K. before initiating PrEP with long-acting cabotegravir are HIV-1/2 antigen/antibody test, HIV RNA, gonorrhea, chlamydia, and syphilis testing. 1

HIV Testing Requirements for Cabotegravir PrEP

Primary HIV Testing

• HIV-1/2 antigen/antibody test AND HIV RNA testing are both required before initiating long-acting cabotegravir PrEP 1
  • This dual testing approach is essential because:
    • T.K.'s most recent sexual activity was 3 weeks ago
    • He reports inconsistent condom use with multiple partners
    • The "window period" for HIV detection necessitates both tests to rule out acute infection
  • HIV RNA testing with a lower limit of quantification of 50 copies/mL or lower is recommended specifically for cabotegravir initiation 1

Rationale for Comprehensive HIV Testing

• Long-acting cabotegravir requires more stringent HIV screening than oral PrEP due to:
  • Risk of developing integrase inhibitor resistance if started during acute HIV infection
  • Potential for delayed and inconsistent detection of HIV (LEVI - long-acting early viral inhibition) 1
  • Diagnostic challenges in the setting of PrEP failure with long-acting agents

STI Testing Requirements

Comprehensive STI Screening

• Gonorrhea, chlamydia, and syphilis testing are essential before PrEP initiation 1
  • T.K. reports multiple sexual partners (5 in past 3 months)
  • He engages in both insertive and receptive anal sex
  • Inconsistent condom use increases his risk for STIs
  • Testing should include specimens from all exposed anatomical sites (rectal, pharyngeal, and urethral)

Clinical Importance

• Untreated STIs increase HIV acquisition risk
• Baseline STI testing allows for prompt treatment if positive
• Regular STI screening is part of ongoing PrEP management

Additional Testing Considerations

Hepatitis B Testing

• While hepatitis B virus (HBV) serologies are important for oral tenofovir-based PrEP, they are less critical for cabotegravir initiation 1
• Cabotegravir has no activity against HBV (unlike tenofovir-based regimens)

Renal Function Testing

• Serum creatinine is essential for oral tenofovir-based PrEP but not specifically required for cabotegravir initiation 1
• Cabotegravir does not have the same renal toxicity profile as tenofovir disoproxil fumarate

Implementation Considerations

Timing of PrEP Initiation

• With a negative rapid antibody test, cabotegravir PrEP may begin while awaiting laboratory test results 1
• The first injection should be administered after confirming negative HIV status through both testing methods

Follow-up Testing

• After initiation, follow-up testing should include:
  • Point-of-care rapid HIV antibody test
  • Laboratory-based antigen/antibody test
  • Regular STI screening every 3 months 1

Common Pitfalls to Avoid

• Do not rely solely on HIV antibody testing - this can miss acute HIV infection
• Do not delay STI testing - untreated STIs increase HIV acquisition risk
• Do not routinely include HIV RNA testing in follow-up monitoring - this has low positive predictive value and can lead to false positives 1
• Do not overlook the importance of adherence counseling for injection appointments, as delays beyond 8 weeks may require oral bridging therapy 2

Long-acting cabotegravir has demonstrated superior efficacy compared to daily oral PrEP in clinical trials, making it an excellent choice for T.K. who reports difficulty with daily pill adherence 3, 4.