Risk assessment and mitigation of hepatitis C virus RNA carryover contamination in a reflex testing algorithm.

Laboratory-based diagnosis of active hepatitis C virus (HCV) infection currently requires a positive antibody test and a confirmatory RNA test. Many institutions in the United States continue to require two separate sample collections, partially due to concerns for carryover contamination. Reflexive RNA testing of antibody-positive samples reduces loss to follow-up, improves linkage to care, and is a recommended operational strategy by the Centers for Disease Control and Prevention. This study describes false positivity rates of reflexive RNA testing in a reference laboratory before and after introduction of a risk mitigation strategy that requires medical director review for reflexed HCV viral loads < 1,000 IU/mL (defined as low-positive). Initial HCV antibody testing was performed at one of five chemistry laboratories; reflex HCV RNA testing was performed using the cobas HCV assay on cobas 8800 (Roche) at a central reference laboratory. A total of 4,079 consecutive positive RNA results were included pre-intervention, and 4,433 were included post-intervention. All low-positive results (