the effectiveness of a re- testing protocol to assure quality dna pcr testing for early infant...
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THE EFFECTIVENESS OF A RE-TESTING PROTOCOL TO ASSURE QUALITY DNA PCR TESTING FOR
EARLY INFANT DIAGNOSIS (EID) IN MALAWI
XVIII INTERNATIONAL AIDS CONFERENCEJULY 18 – 23 2010, VIENNA AUSTRIA
Wainings Manda-EID Lab Coordinator
R Mwenda, H Moyo, J.Bitilinyu, C Porter, M Kabue, M Eliya
HUTAP
Malawi Demographic Profile 2008 Population: 13.6 Million
HIV/AIDS Prevalence -Adult and adolescents: 12%
HIV/AIDS – In children: 30,000 new infections annually
U5MR: 110 deaths per 1,000 live births
DNA PCR Laboratory Capacity EID was implemented in Malawi in 2007 Currently 2 government labs perform
PCR
Infants <18 months are testing using DNA PCR on dried blood spots (DBS)
A total of 18,000 infants were tested at the end of 2009.
A total of 4000 HIV-infected infants were identified
DNA-PCR Testing Protocol Initial negative result – reported
Initial positive result
- re-tested
- confirmed pos results are reported
Indeterminate results are retested in duplicate
Invalid- request for a fresh specimen
Quality Assurance Internal Quality Control
Review results before reporting
Inter-laboratory QC
Proficiency Testing & re-testing (CDC-Atlanta)
Staff competency
18,000 DNA-PCR tests by end of 2009
Purpose EID scale up resulting in higher volume
Current protocol requires re-testing all positive results
Re-testing:- expensive- time consuming
Evaluation of retesting protocol was necessary
Methods
DNA-PCR test results done in 2009 analyzed.
Assessment of the second test result for all specimens with initial;
- positive result
- indeterminate result
- invalid result
Electronic data of DNA PCR results were analyzed using STATA™ version 8.
Discordance: Initial vs. 2nd test
Name of Laboratory
Number of specimens with initial
positive test
Number of specimens with
discordant 2nd test result
Proportion of
discordance
KCH 731 83 11.35%
QECH 1358 153 11.27%
TOTAL 2,089 236 11.31%
Frequency of discordance: 2nd test
HIV Negative Indeterminate Invalid0
20
40
60
80
100
KCH QECH
Conclusion
89% of initial positives were confirmed positive on re-test
A majority of the discordant specimens re-tested yielded HIV negative results
Re-testing is necessary
Lessons learnt
High sensitivity of test assay may contribute to initial false positive results.
Other factors that may lead to initial false positive results are;
- human error
- contamination of specimens
Re-testing specimens rules out false positive results.
Recommendations
Malawi should continue with the current protocol of re-testing all initial DNA-PCR HIV positive results and discordant results.
More specific assays are needed.
Urgently request for re-collection of DBS specimen for invalid result
DNA-PCR operation