Hepatitis C test. Sample vials of human blood serum after tests for antibodies to hepatitis C virus (HCV). This is a Monolisa EIA (enzyme immunoassay) test. This involves adding a patient's blood serum to antigens produced by the virus. Antibodies in infected blood react with the antigens, and an enzyme effects a colour change. The blood serum in the multi-well sample tray shows a positive result by turning yellow. The four yellow tubes in a row are test controls. The other yellow tubes indicate that that blood contains antibodies for hepatitis C virus. Hepatitis C is a serious liver infection most commonly contracted after blood transfusions.