Guidelines for HIV Rapid Test Kits

Evaluation

George Alemnji, Ph.D.

Laboratory Advisor

GAP CDC Caribbean Regional Office

Email:ikv3@cdc.gov

1

2

HIV Rapid Test

Qualitative assay to detect HIV antibodies

Most test kits detect HIV 1 and HIV 2

As reliable as ELISAs

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

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

Body Fluids Used for HIV Rapid Testing

Serum

Plasma

Whole blood

Oral fluids

Urine

5

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

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

7

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

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

Select the Gold Standard

“ Reference Algorithm and Test Kits Used to Score

Evaluation Results’’

10

Key Prior Activities

Develop protocol

Obtain ethical clearance

Procure kits, supplies, etc.

Conduct training for lab staff

Pilot test logistics of plan

11

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.

12

Calculating Sensitivity, Specificity,

PPV, & NPV

13

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

14

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

15

Advantages of National Testing

Strategies and AlgorithmsFacilitates:

Country-level standardization

Procurement and supply management

Training

Quality assurance

16

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

17

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.

18

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)

20

21

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*

22

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

23

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

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.

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

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

Acknowledgement