Reflex testing – definitions We define reflex testing as a linked HCV RNA NAT (or HCVAg) test that is triggered among all people who have an initial positive HCV antibody screening test result. Reflex HCV RNA testing may be implemented in two ways: either laboratorybased reflex testing or clinic-based reflex testing.

• Laboratory-based HCV reflex testing refers to a testing algorithm in which patients have only a single clinical encounter and one blood draw or specimen for an initial laboratory-based HCV antibody test (in some cases it may be divided in two tubes), which is then sent to the lab. If the sample for HCV antibody testing in the lab is positive, then the same existing or duplicate sample is automatically used for a prompt “reflex” laboratorybased HCV RNA (or HCVAg) test. The result returned to the patient/doctor is, therefore, for both the HCV antibody result and, if that is positive, the HCV RNA result. No further visit or specimen collection is required.
• Clinic-based reflex testing refers to a testing algorithm where there is only a single clinical encounter/visit for an initial rapid diagnostic HCV antibody test, but with two blood draws. A fingerstick specimen is first taken and tested using a rapid diagnostic HCV antibody test, which, if positive (after usually a 15-minute wait), is then immediately followed by a “reflex” second blood specien collection (either venous blood specimen or fingerstick) for HCV RNA detection of current infection. The second blood specimen for HCV RNA testing may either be sent to a laboratory for HCV RNA (or HCVAg) test or tested onsite using a POC HCV RNA assay.

Implementation considerations Choice of laboratory-based reflex testing or clinic-based reflex HCV RNA testing for different country contexts Countries should incorporate routine reflex HCV RNA NAT testing into their national testing guidelines and testing infrastructure. The choice between laboratory-based reflex testing and clinic-based reflex testing with POC HCV RNA NAT tests will depend on national testing policies, budgets, infrastructure and human resources, as well as the extent of reliance on centralized high-throughput laboratories, the available sample transport network and location of testing and treatment services. To meet the needs of different populations or regions in a country, a mix of clinic-based and laboratory-based reflex testing strategies may be optimal.

• A laboratory-based reflex testing approach will be more appropriate in settings with large testing volumes supported by extensive specimen transport networks.
• A clinic-based reflex sample collection approach to HCV RNA testing may be preferred for populations such as key populations (particularly, people who inject drugs and men who have sex with men) and in primary care settings, where RDT testing is widely used.