Hepatitis C virus

• Most new infectious in NZ are associated with intravenous drug use.
• Other risk factors include blood transfusion in NZ prior to 1992, migration or healthcare received from a high incidence country, incarceration, tattooing in non-licensed premises.
• Most infections are asymptomatic.

HCV is now highly curable due to potent new treatments. However, reinfection is possible, as immunity does not develop.

Test for HCV in people with risk factors or abnormal liver tests.

Depends on whether already known to have a positive antibody

Serology (HCV antibody) is the first line test for diagnosis in people who have not tested positive before. It indicates infection at some point in time.

• Excellent sensitivity – a negative test excludes hep C infection (unless exposure has occurred within the last few months).
• Excellent specificity – a positive result confirms infection with HCV at some stage, but does not necessarily mean the patient has active infection.

HCV core antigen or HCV RNA (HCV PCR/viral load) give the same information and distinguish resolved from active infection

• In our laboratory, HCV core antigen is added on automatically to patient samples that test positive for HCV antibody, to determine active infection status.
• Excellent sensitivity – a negative antigen result excludes active infection in almost all people (HCV core antigen may be negative in people with lower viral loads, however this is uncommon). The combination of a positive HCV antibody with a negative core antigen/RNA indicates cleared/past infection.
• Excellent specificity – a positive result confirms active infection.
• HCV RNA also used to confirm cure from virus 12 weeks after completing treatment.

HCV antibody testing in people who have tested positive in the past.

• HCV antibody remains positive life-long, even with clearance of the virus. Repeat testing does not give any information as to whether the person has active infection or not.
• Request HCV RNA or HCV core antigen if determination of active infection status is required in those who have had a positive antibody in the past.

Genotyping

• Because current treatments are effective on all genotypes this is no longer routinely required.