Guidelines for HIV Rapid Test Kits
Evaluation
George Alemnji, Ph.D.
Laboratory Advisor
GAP CDC Caribbean Regional Office
Email:[email protected]
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HIV Rapid Test
Qualitative assay to detect HIV antibodies
Most test kits detect HIV 1 and HIV 2
As reliable as ELISAs
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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
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
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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
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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 IgMantibodies
Cost per test and possibility for bulk purchase
Storage requirements
Point of care possibility
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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
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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)
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Key Prior Activities
Develop protocol
Obtain ethical clearance
Procure kits, supplies, etc.
Conduct training for lab staff
Pilot test logistics of plan
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Evaluating Test PerformanceSensitivity (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.
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Calculating Sensitivity, Specificity,
PPV, & NPV
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B+DA+CTotal
C+DDCNegative
A+BBAPositive
TotalHIV -uninfected
Actual HIV status (Gold Standard)Test
result HIV infected
Sensitivity = A ÷ (A+C)
Specificity = D ÷ (B+D)
Positive Predictive Value = A ÷ (A+B)
Negative Predictive Value = D ÷ (C+D)
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
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Testing Algorithms Should be
Developed at National LevelKey Steps :
Identify appropriate tests
Develop algorithm
Build consensus
Develop policy
Bring into national scale
Review testing algorithms annually
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Advantages of National Testing
Strategies and AlgorithmsFacilitates:
Country-level standardization
Procurement and supply management
Training
Quality assurance
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Serial vs. Parallel Testing
Serial 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 (tie-breaker) is required
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Only Three Possible Outcomes for
Single HIV Antibody TestReactive 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.
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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 (tie-breaker) or
Participant asked to come back for redraw 19
Tie-Breaker Test
When two test results are different, the 3rd 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)
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Blood Sample
Test 1
Test 3
Test 2
Both
Reactive
Report
Positive
Discordant
Result
Reactive
Result
Report
Positive
Non-reactive
Result
Report
Negative
Both
Non-reactive
Report
Negative
Parallel Testing Algorithm*
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Parallel Algorithm: Possible
OutcomesTEST 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 PositiveLab workers Health workers Counselors
Serial Testing Algorithm
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1st test
Non-reactive
2nd testInterpretation:
Negative
Reactive
Discordant results:
3rd test tie-breaker
Interpretation:
Positive
Reactive Non-reactive
Interpretation:
Negative
Non-reactive
Interpretation:
Positive
Reactive
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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.
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??????
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