False negatives may occur in the window phase prior to seroconversion in immunosuppressed patients, those on hemodialysis, and patients who have had prior chemotherapy, who may not mount an anti-HCV antibody response. A positive for at least two antigens is a positive test and implies that a previous positive anti-HCV test was a true positive. One positive antigen is considered indeterminate and none, negative. However, the PCR test is not very well standardized. Results vary with the individual laboratory.
Decisions regarding initiating treatment also vary with the risk group.
If the RIBA is indeterminate or negative, hepatitis C is unlikely. The progress of therapy is monitored by RNA tests. The qualitative PCR test, the most sensitive test currently available, detects HCV viremia, expressed as present or absent. Quantitative assays measure viral particles. This is particularly important when viral counts are low.