Abstract
BackgroundExpansion of HIV viral load (VL) testing services are required to meet increased targets for monitoring patients on antiretroviral treatment. South Africa currently tests >4million VLs per annum in 16 highly centralised, automated high-throughput laboratories. The Xpert HIV-1 VL assay (Cepheid) was evaluated against in-country predicates, the Roche Cobas Taqmanv2 and Abbott HIV-1RT, to investigate options for expanding VL testing using GeneXpert’s random access, polyvalent capabilities and already established footprint in South Africa with the Xpert MTB/RIF assay (207 sites). Additionally, the performance of Xpert HIV-1VL on alternative, off-label specimen types, Dried Blood Spots (DBS) and whole blood, was investigated.MethodPrecision, accuracy (agreement) and clinical misclassification (1000cp/ml) of Xpert HIV-1VL plasma was compared to Taqmanv2 (n = 155) and Abbott HIV-1 RT (n = 145). Misclassification of Xpert HIV-1VL was further tested on DBS (n = 145) and whole blood (n = 147).ResultsXpert HIV-1VL demonstrated 100% concordance with predicate platforms on a standardised frozen, plasma panel (n = 42) and low overall percentage similarity CV of 1.5% and 0.9% compared to Taqmanv2 and Abbott HIV-1 RT, respectively. On paired plasma clinical specimens, Xpert HIV-1VL had low bias (SD 0.32–0.37logcp/ml) and 3% misclassification at the 1000cp/ml threshold compared to Taqmanv2 (fresh) and Abbott HIV-1 RT (frozen), respectively. Xpert HIV-1VL on whole blood and DBS increased misclassification (upward) by up to 14% with increased invalid rate. All specimen testing was easy to perform and compatible with concurrent Xpert MTB/RIF Tuberculosis testing on the same instrument.ConclusionThe Xpert HIV-1VL on plasma can be used interchangeably with existing predicate platforms in South Africa. Whole blood and DBS testing requires further investigation, but polyvalency of the GeneXpert offers a solution to extending VL testing services.
Highlights
HIV viral load (VL) testing is used to monitor the effectiveness of antiretroviral therapy (ART) after treatment initiation, identify early virological failures to target adherence counselling and guide treatment switch [1]
Xpert HIV-1VL demonstrated 100% concordance with predicate platforms on a standardised frozen, plasma panel (n = 42) and low overall percentage similarity CV of 1.5% and 0.9% compared to Taqmanv2 and Abbott HIV-1 RT, respectively
On paired plasma clinical specimens, Xpert HIV-1VL had low bias (SD 0.32–0.37logcp/ml) and 3% misclassification at the 1000cp/ml threshold compared to Taqmanv2 and Abbott HIV-1 RT, respectively
Summary
HIV viral load (VL) testing is used to monitor the effectiveness of antiretroviral therapy (ART) after treatment initiation, identify early virological failures to target adherence counselling and guide treatment switch [1]. All VL testing requirements to service these clinics is performed and managed by the National Health Laboratory service (NHLS) with oversight from the National Priority Programme (NPP), through 16 centralised VL laboratories across the 9 provinces. To ensure that VL testing volume requirements are met and are within a clinically relevant turnaround time, a hybrid testing model consisting of both laboratory and point of care testing (POCT), as recently proposed for CD4 testing services [3], may be required Adapting this model for VL testing could require the expansion of existing centralised, high-throughput VL testing capacity, dried blood spot (DBS) specimen transport and testing and extension of VL testing services to lower throughput decentralised sites. The performance of Xpert HIV1VL on alternative, off-label specimen types, Dried Blood Spots (DBS) and whole blood, was investigated
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