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. 2. 3.
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