Laboratory investigation of low positive and discrepant HIV serology results

Abstract

In our diagnostic virology laboratory, we test on average 1500 samples for HIV antibody/antigen each month, of which 0.6% produces problematic results. These problematic samples produce either weakly reactive screening and confirmatory results or, discrepant screening and confirmatory results. Both scenarios require additional tests to confirm HIV status thus increasing cost and turnaround time. There is a need to devise an optimal strategy within the laboratory to rapidly and easily manage these samples with minimal additional cost. The WHO recommends three HIV testing strategies. Strategy I ensures blood transfusion safety while strategies II and III are used for both surveillance and diagnostics in high prevalence and low prevalence areas respectively.1The 2010 National antenatal sentinel HIV & syphilis prevalence study reported the South African HIV prevalence as 30.2%.2 There were 1.8 million new cases of HIV infection in Sub-Saharan Africa in 2011.3South Africa (SA) is a high prevalence country and therefore the national HIV testing guideline is based on strategy II. The HIV screening and confirmatory strategy at Groote Schuur is based on these recommendations.