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False positive HIV screening test among syphilis patients

A Azraan

Reasons for false HIV positive screening test • Cross-reactive antibodies to some human leukocyte antigens (HLA) that develop as the result of prior blood transfusion or during multiple pregnancies • Auto-antibodies found in some rheumatologic diseases • Receipt of gamma-globulin • Recent vaccination (influenza, hepatitis) • Renal transplantation • Some liver diseases • Some cancers • EBV infection • Technical errors in testing Pitfalls in HIV testing. Application and limitations of current tests. Cordes RJ1, Ryan ME. Postgrad Med. 1995 Nov;98(5):177-80, 185-6, 189.

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• False positive HIV • Syphilis and false positive HIV

Available screening tests for HIV 1. HIV enzyme linked immunosorbent assay ( HIV Elisa ) – Gens screen 2. Particle agglutination Test (PA) - Serodia 3. Rapid Test kits Sensitivity

Specificity

HIV Elisa (4th G )

100

99.9

HIV Elisa (3rd G )

99.3

99.7

HIV PA (serodia)

100

99.8

Test

Testing algorithm A1 Reactive / inconclusive

A1 and A2

Negative

Second Sample for confirmation

Reactive or inconclusive one test

Both Negative

A3

Positive

Indeterminate

Negative

Follow up • Western Blot : 2 envelope protein ¹ gag or pol Indeterminate results on WB Repeat in 6 week with appropriate strategy Longer follow up 3,6 and 12 months If indeterminate beyond 1 year, declare as negative

Study method • A case series • Clinic based descriptive study • Selected cases from 3 clinics from 2007-2013 – Central STD clinic – STD Clinic Kalubowila – STD clinic Ragama

• Eligibility criteria

– Positive syphilis serology at the time of diagnosis – Positive or indeterminate HIV screening test at the time of diagnosis of syphilis – Subsequent negative or indeterminate HIV confirmatory test results

Results • 24 cases identified.

Clinic representation 1, 4%

10, 42% 13, 54%

Central Clinic Kalubowila Clinic Ragama Clinic

Sex distribution

Age distribution 12 10 8

4, 17% Male Female 20, 83 %

6 4 2 0 10-19 20-29 30-39 40-49 50+ age

Initial HIV screening test

11, 46% 13, 54%

ELISA PA

Stage of syphilis

Initial VDRL titer 8 7

1, 4%

5, 21% 11, 46 %

7, 29%

Primary syphilis

6

Secondar y syp

4

5

Early latent

3

SUD

1

75%

2 0 R8

R16

R32

R64

R128

HIV test result of the second sample Case

Particle agg. test

ELISA

Confirmatory (WB/LB)

Case 1

Indeterminate

Negative

Negative

Case 2

Not done

Negative on 2 tests

Not done

Case 3

Indeterminate

Negative

Negative

Case 4

Negative

Negative

Not done

Case 5

Reactive

Negative

Negative

Case 6

Indeterminate

Negative

Negative

Case 7

Indeterminate

Negative

Negative

Case 8

Indeterminate

Negative

Negative

Case 9

Indeterminate

Negative

Negative

Case 10

Reactive

Negative

Negative

Case 11

Reactive

Negative

Indeterminate

Case 12

Reactive

Negative

Indeterminate

Case 13

Reactive

Weakly reactive

Indeterminate

Case 14

Indeterminate

Weakly reactive

Negative

Case 15

Negative

Reactive

Negative

Case 16

Negative

Weakly reactive

Negative

Case 17

Negative

Reactive

Indeterminate

Case 18

Negative

Weakly reactive

Negative

Case 19

Negative

Reactive

Negative

Case 20

Indeterminate

Weakly reactive

Indeterminate

Case 21

Negative

Weakly reactive

Negative

Case 22

Negative

Weakly reactive

Indeterminate

Case 23

Negative

Weakly reactive

Negative

Case 24

Negative

Weakly reactive

Indeterminate

Initial HIV confirmatory test Total cases

24

Confirmatory test results

Cases

Indeterminate

07

Negative

15

Not done

02

Treatment response Treatment modality 18 16 14 12 10 8 6 4 2 0

Treatment response

7, 29%

4 fold drop 17, 71 %

defaulted

Follow up HIV testing Total cases

Confirmatory test results

Indeterminate

Cases

07

Follow up HIV screening & confirmatory in appropriate cases

Negative (05) Default (02)

24

Negative

15

Negative (08) Default (07)

Not done

02

Negative (01) Default (01)

VDRL titer at subsequent HIV test

Initial VDRL titer

8

8 7 6 5 4 3 2 1 0

7 6 5 4 3 2 1 0 R8

R16

R32

R64

R128

Summary • Out of 24 cases with reactive or indeterminate HIV screening test results, 22 became negative subsequently.

• Almost all cases (23) were diagnosed as early syphilis.

• 17 cases were excluded HIV infection initially by confirmatory test and 5/7 of the remaining were excluded by subsequent tests.

Conclusion • Possibility of false positive HIV screening test in early syphilis with high VDRL titer.

Acknowledgement • Dr. N. Abeygunasekara. Consultant Venereologist. STD clinic – Kalubowila

References 1.

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