Performance of rapid HIV tests used singly and in combination:

Moving toward a point of care diagnosis.

Kevin Delaney, MPHHIV Diagnostics: New Developments and

ChallengesMarch 1, 2005

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”

Background

• 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.”

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

• Location – Two clinics in Los Angeles, CA

• Participants– Persons of unknown serostatus seeking HIV

testing– Persons known to be HIV positive

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)*

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)

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

Methods

Initial Rapid Test Screen

2nd Rapid test Screen

Third Rapid Test “Tie-Breaker”

Confirmed Positive

Confirmed Negative

Negative

Positive Positive

Negative

Negative

Positive

Sequential Antibody Screening Algorithm

Sample Size≈ 4800 total participants

(including known positives)

≈ 4400 total participants Not on antiretroviral therapy

≈ 2400 total participants tested

≈ 800 EIA/WB+ ≈ 4000 EIA Negative

≈ 400positives on treatment

Results – SensitivityTest Specimen

typeRT + False

negSensitivity (95% CI)

Oraquick Oral fluid 400 2 99.5 (98.2-99.9)Whole blood 401 0 100 (99.3-100)

Unigold Whole blood 139 1 99.3 (96.1-100)Plasma 245 1 99.6 (97.8-100)

Stat-pak Whole blood 257 3 98.9 (96.7-99.8)Plasma 366 2 99.5 (98.1-99.9)

Reveal Serum 397 2 99.5 (98.2-99.9)

Results – SensitivityTest Specimen

typeRT + False

negSensitivity (95% CI)

Oraquick Oral fluid 400 2 99.5 (98.2-99.9)Whole blood 401 0 100 (99.3-100)

Unigold Whole blood 139 1 99.3 (96.1-100)Plasma 245 1 99.6 (97.8-100)

Stat-pak Whole blood 257 3 98.9 (96.7-99.8)Plasma 366 2 99.5 (98.1-99.9)

Reveal Serum 397 2 99.5 (98.2-99.9)

Results – Specificity, single rapid test

Test Specimen type

RT neg

False +

Specificity (95% CI)

Oraquick Oral fluid 4156 1 100 (99.9-100)

Whole blood 4171 1 100 (99.8-100)

Unigold Whole blood 2282 0 100 (99.9-100)Plasma 2288 0 100 (99.9-100)

Stat-pak Whole blood 3442 0 100 (99.9-100)Plasma 3435 2 99.9 (99.8-100)

Reveal Serum 4155 3 99.9 (99.6-100)Multispot Plasma 487 0 100 (99.4-100)

Results – Specificity, POC rapid tests

Test Specimen type

RT neg

False +

Specificity (95% CI)

Oraquick Oral fluid 4156 1 100 (99.9-100)

Whole blood 4171 1 100 (99.8-100)

Unigold Whole blood 2282 0 100 (99.9-100)

Stat-pak Whole blood 3442 0 100 (99.9-100)

Results – Specificity, POC rapid tests

Test Specimen type

RT neg

False +

Specificity (95% CI)

Oraquick Oral fluid 4156 1 100 (99.9-100)

Whole blood 4171 1 100 (99.8-100)

Unigold Whole blood 2282 0 100 (99.9-100)

Stat-pak Whole blood 3442 0 100 (99.9-100)

98.399.2 10099.291.6

96.296.1 100

76.6

88.288.1100

0

20

40

60

80

100

Oraquick Oral fluid Oraquick Whole Blood Unigold/Stat-pak WholeBlood

Stat-pak Plasma(Sp=99.94)

5.0% 1.0% 0.3%

PV+

Results – Predictive value positive, single rapid test

Prevalence

Results – Sequential testing, 1st testTests Algorithm Results Comparison to

EIA/WB

1st test - +

OQ-b 2234 135

OQ-b 2234 136

OQ-o 2235 135

OQ-o 2235 135

UG 2235 135

UG 2235 135

UG 2235 135

SP 2238 133

SP 2238 131

SP 2238 132

Results – Two tests used sequentiallyTests Algorithm Results Comparison to

EIA/WB

1st test2nd test

-nd

++

+-

OQ-b UG 2234 133 2

OQ-b SP 2234 132 4

OQ-o UG 2235 133 2

OQ-o SP 2235 131 4

UG OQ-b 2235 135 0

UG OQ-o 2235 134 1

UG SP 2235 132 3

SP OQ-b 2238 132 1

SP OQ-o 2238 131 0

SP UG 2238 132 0

Tests Algorithm Results Comparison to EIA/WB

1st test2nd test

3rd test

-nd nd

++nd

+-+

+--

OQ-b UG SP 2234 133 1 1

OQ-b SP UG 2234 132 3 1

OQ-o UG SP 2235 133 1 1

OQ-o SP UG 2235 131 3 1

UG OQ-b 2235 135 0 0

UG OQ-o SP 2235 134 1 0

UG SP OQ-b 2235 132 3 0

OQ-o 2235 132 3 0

SP OQ-b 2238 132 0 0

SP OQ-o UG 2238 131 1 0

SP UG 2238 132 0 0

Results – Adding the 3rd test

Results – Adding the 3rd testTests Algorithm Results Comparison to

EIA / WB

1st test2nd test

3rd test

-nd nd

++nd

+-+

+--

False Pos

False Neg

OQ-b UG SP 2234 133 1 1 0 0

OQ-b SP UG 2234 132 3 1 0 0

OQ-o UG SP 2235 133 1 1 0 1

OQ-o SP UG 2235 131 3 1 0 1

UG OQ-b 2235 135 0 0 0 0

UG OQ-o SP 2235 134 1 0 0 0

UG SP OQ-b 2235 132 3 0 0 0

OQ-o 2235 132 3 0 0 0

SP OQ-b 2238 132 0 0 0 0

SP OQ-o UG 2238 131 1 0 0 3

SP UG 2238 132 0 0 0 3

10098.399.2 10099.2 10091.6

96.296.1100 100

76.688.288.1

100

0

20

40

60

80

100

Oraquick Oral fluid Oraquick WholeBlood

Unigold/StatpackWhole Blood

Statpack Plasma Multitest Algorithm

5.0% 1.0% 0.3%

PV+

Results – Predictive value positive, single rapid test v. multitest algorithm

Prevalence

• Imperfect “Gold Standard” (EIA/Western blot)– Clinical follow-up is the “true gold” standard– Plan perform additional testing on residual specimens to

address 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

Limitations

• 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

Summary

• 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)

Discussion

• 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

Next Steps

• For discussion– More pros and any cons– Implementation barriers

• What do we need to do to catch up to Zimbabwe and Botswana?

Outstanding Questions