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Kevin Delaney, MPH HIV Diagnostics: New Developments and Challenges March 1, 2005

Performance of rapid HIV tests used singly and in combination: Moving toward a point of care diagnosis. Kevin Delaney, MPH HIV Diagnostics: New Developments and Challenges March 1, 2005. Background. Rapid test combinations

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Kevin Delaney, MPH HIV Diagnostics: New Developments and Challenges March 1, 2005

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  1. Performance of rapid HIV tests used singly and in combination: Moving toward a point of care diagnosis. Kevin Delaney, MPH HIV Diagnostics: New Developments and Challenges March 1, 2005

  2. Background • Rapid test combinations • Many countries throughout the world use multi-test algorithms for HIV confirmatory testing • 4 FDA-approved tests • 2 CLIA-waived • more likely on the way • US experience to date • “Traditional” outreach testing → Rapid testing • Provide immediate results • Negative • “Preliminary Positive”

  3. All FDA approved rapid HIV test package inserts now state: “This test is suitable for use in multi-test algorithms designed for statistical validation of rapid HIV test results. When multiple rapid HIV tests are available, this test should be used in appropriate multi-test algorithms.” Background

  4. Objectives • Describe the performance of individual rapid tests • Sensitivity, specificity and predictive value • Evaluate the performance of combinations of rapid tests used in sequence • Particular focus on tests designed for use at point of care • Foster discussion of a point of care diagnostic algorithm

  5. Methods • Location • Two clinics in Los Angeles, CA • Participants • Persons of unknown serostatus seeking HIV testing • Persons known to be HIV positive

  6. Methods • Testing • Multiple specimens from participants were tested with several rapid tests including: • Multispot (Serum and plasma)* • Oraquick (Oral fluid, whole blood and plasma) • Reveal (Serum and plasma) • STAT-PAK (Whole blood and plasma) • Unigold (Whole blood and plasma)*

  7. Methods • Testing • Serum also tested with EIA and Western blot: • Vironostika HIV-1 Microelisa system • Genetic Systems HIV-1 Western Blot • Samples of both serum and plasma retained for future testing (e.g. RNA NAT, DNA NAT, other EIAs)

  8. Methods • Analysis • Single rapid test results compared to EIA/WB • Sensitivity, specificity and predictive value • Rapid test algorithms simulated using results of rapid tests as if they were performed sequentially • Specificity and predictive value positive

  9. Sequential Antibody Screening Algorithm Initial Rapid Test Screen 2nd Rapid test Screen Positive Positive Negative Third Rapid Test “Tie-Breaker” Negative Positive Negative Confirmed Positive Confirmed Negative

  10. Sample Size ≈ 4800 total participants (including known positives) ≈ 800 EIA/WB+ ≈ 4000 EIA Negative ≈ 400 positives on treatment ≈ 4400 total participants Not on antiretroviral therapy ≈ 2400 total participants tested

  11. Results – Sensitivity

  12. Results – Sensitivity

  13. Results – Specificity, single rapid test

  14. Results – Specificity, POC rapid tests

  15. Results – Specificity, POC rapid tests

  16. Results – Predictive value positive, single rapid test PV+ Prevalence

  17. Results – Sequential testing, 1st test

  18. Results – Two tests used sequentially

  19. Results – Adding the 3rd test

  20. Results – Adding the 3rd test

  21. Results – Predictive value positive, single rapid test v. multitest algorithm PV+ Prevalence

  22. Limitations • Imperfect “Gold Standard” (EIA/Western blot) • Clinical follow-up is the “true gold” standard • Plan perform additional testing on residual specimens toaddress sensitivity of gold standard • Lack of complete testing data for all specimens • Testing was performed by trained technicians • Not counselors, nurses or others who might do testing in outreach settings

  23. Summary • Sensitivity of all rapid tests was >98% • Comparable to current EIAs • Negative predictive value suggests < 2 false negatives/10,000 negatives tested @ 1% prevalence • Important to consider “realized sensitivity” • Specificity of a single rapid test >99% • At low prevalence, the proportion of positive tests that are false positive increases. • Adding a second different rapid test increased specificity to 100% for specimens reactive on both tests • 0-4 specimens required a third “tie-breaker” rapid test

  24. Discussion • Data suggest ANY combination of rapid tests gives results comparable to EIA/Western blot algorithm • Use of combinations of waived tests would allow for POC testing and immediate return of confirmed results for both negatives and positives • Cost of rapid tests ≈ ½ cost of a Western blot; suggesting opportunity for significant cost savings • Other factors warrant consideration (e.g. CLIA status, ease of use, biohazards with different specimen types, shelf life, differentiation of HIV-2)

  25. Next Steps • Need clinical follow-up of persons with discordant results – the true gold standard • Evaluate on larger numbers • Compare the sensitivity of rapid tests to NAT, 3rd and 4th generation EIAs • Validate use of a POC diagnostic algorithm in a variety of field and clinical settings

  26. Outstanding Questions • For discussion • More pros and any cons • Implementation barriers • What do we need to do to catch up to Zimbabwe and Botswana?

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