The Centers for Disease Control and Prevention (CDC) recommends hepatitis C virus (HCV) antibody (anti-HCV) testing for people who have certain risk factors, including all individuals born between 1945–1965 and those with a history of injection drug use, persistently elevated alanine aminotransferase levels, a blood or organ transplant before 1992, clotting factor concentrates before 1987, or long-term hemodialysis. Also, the U.S. Public Health Service and the Infectious Diseases Society of America recommend HCV screening for those with HIV.

Still, even with these recommendations, the question remains: Just how effective is such screening at identifying those with HCV? A new study, “Hepatitis C Virus Antibody Positivity and Predictors Among Previously Undiagnosed Adult Primary Care Outpatients: Cross-Sectional Analysis of a Multisite Retrospective Cohort Study,” sought to answer that question. The researchers found that risk-based HCV screening may have missed four out of five newly enrolled patients who were anti-HCV-positive.

The researchers retrospectively analyzed data from electronic medical records at four sites. The study participants were 18 or older, went to primary care one or more times between 2005 and 2010, and had no previous HCV diagnosis.

For the purpose of this research, “anti-HCV positivity” was defined as a positive test result for antibodies to HCV by enzyme-linked immunoassay at any visit during the study period. A total of 209,076 patients were observed for 5 months; 17,464 patients who were tested for anti-HCV received positive results. The study found that history of injection drug use, being born between 1945 and 1965, and elevated alanine aminotransferase levels were independently associated with positive anti-HCV test results. The study authors estimated that 81.5% of anti-HCV-positive patients were not identified using risk-based testing.

Among the patients tested for anti-HCV in this study, 6.4% had positive test results. About 75% of the anti-HCV-positive people in the study were born between 1945 and 1965, and anti-HCV positivity was significantly higher in this group (13.8%) compared with the referent group of those born either before 1945 or after 1965 (2.5%).

“Without knowing their status, unidentified anti-HCV[-positive] persons cannot receive further clinical evaluation or antiviral treatment, and are unlikely to benefit from secondary prevention recommendations to limit disease progression and mortality,” the study authors concluded.