U.S. guidelines for hepatitis C virus (HCV) testing may miss up to a quarter of cases, according to new research. Publishing their findings in Clinical Infectious Diseases, researchers at the Johns Hopkins Hospital Emergency Department reviewed blood samples for nearly 5,000 patients.

The Centers for Disease Control and Prevention (CDC) recommends a one-time hep C screening for those born between 1945 and 1965 and for those with risk factors such as injection drug use, HIV or the use of clotting factors. In November 2015, the Johns Hopkins Hospital expanded its own testing guidelines to include all those who visit its emergency department who are 18 and older, have their blood drawn for routine care and are not known to have hep C antibodies.

Fourteen percent of the 5,000 individuals tested positive for hep C; one third of them were not aware of their infection.

To read a press release about the study, click here.