Guidelines for HIV Rapid Test Kits Evaluation

Transcription

1 Guidelines for HIV Rapid Test Kits Evaluation George Alemnji, Ph.D. Laboratory Advisor GAP CDC Caribbean Regional Office 1

2 HIV Rapid Test Qualitative assay to detect HIV antibodies Most test kits detect HIV 1 and HIV 2 As reliable as ELISAs 2

3 HIV Rapid Testing : Advantages Increases access to prevention (VCT) and interventions (PMTCT) Supports increased number of testing sites Same-day diagnosis and counseling Robust and easy to use Test time under 30 minutes Most require no refrigeration Minimal or no equipment required Minimum technical skill 3

4 HIV Rapid Testing : Disadvantages Small numbers for each test run Quality Assurance/Quality Control at multiple sites Test performance varies by product Reader variability in interpretation of results 4

5 Body Fluids Used for HIV Rapid Testing Serum Plasma Whole blood Oral fluids Urine 5

6 Getting Set for Evaluation Decide and verify source samples to be included in the panel Decide type of evaluation Lab evaluation only (phase I) Field evaluation only (phase II) Lab and field evaluation 6

7 Getting Set for Evaluation cont. Select test kits to be evaluated based on: Documented ability of the test to detect HIV-1 (group M and O) and HIV-2 Documented ability to detect IgG and IgM antibodies Cost per test and possibility for bulk purchase Storage requirements Point of care possibility 7

8 Getting Set for Evaluation cont. Select test kits to be evaluated based on: Ease of use; Simplicity of test procedure Experience with the assay(s) Availability Shelf-life and robustness Laboratory infrastructure 8

9 Getting Set for Evaluation cont. Be sure of sample and kits integrity Avoid freezing and thawing during evaluation Aliquot samples into vials Determine sample size Minimum 200 positives (WHO) Minimum 200 Negatives (WHO) Include well characterized panels (HIV-1 group O, HIV-2, recent infection) 9

10 Select the Gold Standard Reference Algorithm and Test Kits Used to Score Evaluation Results 10

11 Key Prior Activities Develop protocol Obtain ethical clearance Procure kits, supplies, etc. Conduct training for lab staff Pilot test logistics of plan 11

12 Evaluating Test Performance Sensitivity (Se) of a test is its capacity to correctly identify people that are infected with HIV. Specificity (Sp) of a test is its capacity to correctly identify people that are not infected with HIV. Positive Predictive Value (PPV) is the probability that a person who tests reactive is indeed infected with HIV. Negative Predictive Value (NPV) is the probability that a person who tests negative is not infected with HIV. 12

13 Calculating Sensitivity, Specificity, PPV, & NPV Test result Positive Negative Total Actual HIV status (Gold Standard) HIV infected A C A+C HIV -uninfected B D B+D Total A+B C+D Sensitivity = A (A+C) Specificity = D (B+D) Positive Predictive Value = A (A+B) Negative Predictive Value = D (C+D) 13

14 Strategies and Algorithms Strategies Testing approach used to meet a specific need, such as: Blood Safety Surveillance Diagnosis Algorithms The combination and sequence of specific tests used in a given strategy 14

15 Testing Algorithms Should be Developed at National Level Key Steps : Identify appropriate tests Develop algorithm Build consensus Develop policy Bring into national scale Review testing algorithms annually 15

16 Advantages of National Testing Strategies and Algorithms Facilitates: Country-level standardization Procurement and supply management Training Quality assurance 16

17 Serial testing Serial vs. Parallel Testing Performing one test at a time Each test result establishes if additional tests and a tie breaker is needed Parallel testing Two tests performed at the same time on the same sample Test results establish if a third test (tiebreaker) is required 17

18 Only Three Possible Outcomes for Single HIV Antibody Test Reactive or Positive Test band Control band Non-reactive or Negative Control band only Invalid No control band present Test has failed. Repeat with new device. 18

19 Test Results Confirmation An HIV-positive status should be based upon the outcome of 2 or more tests When two test results disagree (one is reactive, the other non-reactive), the finding is called discordant. < 5% In this case: Either third test performed (tiebreaker) or Participant asked to come back for redraw 19

20 Tie-Breaker Test When two test results are different, the 3 rd test is called the tie-breaker For the tie-breaker, use either a third rapid test (immediate results) OR an ELISA test (results generally not available the same day) 20

21 Parallel Testing Algorithm* Blood Sample Test 1 Test 2 Both Reactive Report Positive Both Non-reactive Report Negative Discordant Result Test 3 Reactive Result Report Positive Non-reactive Result Report Negative 21

22 Parallel Algorithm: Possible Outcomes TEST 1 TEST 2 TEST 3 HIV Status Non-reactive Non-reactive Negative Reactive Reactive Positive Non-reactive Reactive Non-reactive Negative Reactive Non-reactive Non-reactive Negative Non-reactive Reactive Reactive Positive Reactive Non-reactive Reactive Positive Lab workers Health workers Counselors 22

23 Serial Testing Algorithm 1 st test Non-reactive Interpretation: Negative Reactive 2 nd test Reactive Interpretation: Positive Non-reactive Discordant results: 3 rd test tie-breaker Non-reactive Interpretation: Negative Reactive Interpretation: Positive 23

24 Key Messages HIV rapid testing is as reliable as ELISA All tests require attention to training, supervision, and monitoring at points of service. As testing is expanding and decentralized, training, supervision, and monitoring must follow accordingly and become all the more important. 24

25 BIG QUESTION Do we need to re-invent the wheel all the time or do we need to carry out HIV rapid test kits evaluation in all countries or at all testing sites? YES????? NO?????? 25

26 Acknowledgement Organizers of CHART-CCAS-CDC Conference All Laboratory Staff Caribbean Region Dr Akin Abayomi Prof. Clive Landis Dr Bharat Parekh Dr John Nkengasong Dr Shirley Lecher 26