Abstract
The 2013 WHO antiretroviral therapy (ART) guidelines recommend dried blood spots (DBS) as an alternative specimen type for viral load (VL) monitoring. We assessed the programmatic utility of screening for antiretroviral (ARV) treatment failure (TF) at 5,000 and 1,000 copies/ml using DBS and dried plasma spots (DPS) with a commonly used VL assay, the Roche Cobas Ampliprep/Cobas TaqMan V.2.0 (CAP/CTM). Plasma, DBS, and DPS were prepared from 839 whole-blood specimens collected from patients on ART for ≥ 6 months at three public facilities in Namibia. Using the CAP/CTM test, VL were measured in plasma, DBS, and DPS, and the results were compared using the plasma VL as the reference standard. The clinical sensitivities, specificities, and positive (PPV) and negative predictive values (NPV) of DBS at ARV TF diagnostic thresholds of 5,000 copies/ml and 1,000 copies/ml were 0.99, 0.55, 0.33, and 0.99 and 0.99, 0.26, 0.29, and 0.99, respectively, and for DPS at TF diagnostic thresholds of 5,000 copies/ml and 1,000 copies/ml, they were 0.88, 0.98, 0.92, and 0.97 and 0.91, 0.96, 0.89, and 0.97, respectively. The prevalences of TF were overestimated in DBS by 33% and 57% at these two thresholds, respectively. A high rate of false-positive results would occur if the CAP/CTM with DBS were to be used to screen for ARV TF. WHO recommendations for DBS-based VL monitoring should be specific to the VL assay version and type. Despite the better performance of DPS, the programmatic utility for TF screening may be limited by requirements for processing the whole blood at the collection site.