Evaluation of Blood Droplet Volumes on the Cobas Plasma Separation Card for HCV RNA Testing in Resource-Limited Settings

Detection of viral RNA is essential for hepatitis C virus (HCV) diagnosis. Collection and preservation of plasma, the preferred specimen type, is challenging in some areas. The Cobas Plasma Separation Card (PSC) is an alternative specimen type with no cold chain requirements. The PSC is designed to use capillary blood from fingerstick and capillary tube collection, but alternative sample collection options would broaden PSC utility. This study explored qualitative and quantitative HCV RNA detection with PSC prepared using a syringe needle, compared to plasma. Using a 24-gauge syringe, blood was drawn by venipuncture from HCV antibody-positive clinic patients aged > 18 years and used to prepare plasma or spotted directly onto three PSCs using 6, 8 and 10 drops per spot (group 1) or 8, 10 and 12 drops (group 2). HCV RNA was measured using the Cobas HCV assay. Test results for all conditions were available for 143 patients in group 1 and 109 patients in group 2. The proportions with detectable HCV RNA were not significantly different from plasma, and overall agreement was over 88% for any PSC spot number (Fisher exact test p > 0.1). The mean HCV viral load was lower for PSC samples vs. plasma for six or eight spots in group 1 but not statistically different for 10 or 12 spots in either group. Direct spotting of blood using a syringe is a viable alternative to finger prick and capillary tube transfer for PSC preparation. This approach may be beneficial in resource-limited settings and in patient populations for whom capillary blood collection is challenging.