What lab test is used to check for hepatitis C (HCV) infection?

Hepatitis C Testing Protocol

The recommended testing sequence for hepatitis C virus (HCV) infection begins with an FDA-approved HCV antibody test, followed by HCV RNA nucleic acid testing (NAT) if the antibody test is reactive, to confirm current infection. 1

Initial Testing for HCV Infection

• Testing for HCV infection should start with either a rapid or laboratory-conducted assay for HCV antibody in blood 1
• A nonreactive HCV antibody result indicates no HCV antibody detected, generally meaning no infection 1
• A reactive HCV antibody result indicates one of three possibilities: current HCV infection, past HCV infection that has resolved, or false positivity 1
• For initial testing, use an FDA-approved test for HCV antibody such as laboratory-based enzyme immunoassays (EIAs) or the OraQuick HCV Rapid Antibody Test 1

Confirmatory Testing

• A reactive HCV antibody test should always be followed by a nucleic acid test (NAT) for HCV RNA to confirm current infection 1
• HCV RNA testing is the definitive way to distinguish between current active infection versus past resolved infection or false positive antibody results 1
• An FDA-approved NAT assay with a detection level of ≤25 IU/mL should be used for HCV RNA testing 1

Testing Procedures

• The most efficient approach is to collect blood for both tests at once, with reflex testing:
  • Option 1: The same sample of venipuncture blood used for initial HCV antibody testing is reflexed to HCV NAT if reactive 1
  • Option 2: From a single venipuncture, two specimens are collected in separate tubes: one for initial HCV antibody testing and a second for HCV NAT if the antibody test is reactive 1
• If using the OraQuick HCV Rapid Antibody Test with fingerstick blood, a separate venipuncture blood sample must be submitted for HCV NAT if the antibody test is reactive 1

Special Populations

• For persons who might have been exposed to HCV within the past 6 months, direct HCV RNA testing or follow-up HCV antibody testing 6 months after exposure is recommended 1
• For immunocompromised persons, HCV RNA testing should be considered even with negative antibody results, as antibody development may be delayed or absent 1, 2
• For persons at risk of reinfection after previous spontaneous or treatment-related viral clearance, HCV RNA testing is recommended because a positive HCV antibody test is expected 1

Interpretation of Results

• HCV antibody nonreactive: No HCV antibody detected, no further action required unless recent exposure is suspected 1
• HCV antibody reactive, HCV RNA detected: Current HCV infection, requiring appropriate counseling and linkage to medical care and treatment 1
• HCV antibody reactive, HCV RNA not detected: No current HCV infection; indicates either past resolved infection or false positive antibody result 1

Additional Considerations

• To differentiate between past resolved infection and false positive antibody results, testing with a second different HCV antibody assay can be considered 1
• Quantitative HCV RNA testing is recommended prior to initiating antiviral therapy to document baseline viral load 1
• HCV genotype testing may be considered for those in whom it may alter treatment recommendations 1

Common Pitfalls to Avoid

• Relying solely on HCV antibody testing without confirmatory HCV RNA testing can lead to misdiagnosis 1, 3
• Failing to consider direct HCV RNA testing in recently exposed or immunocompromised patients can miss early infections 1, 2
• Not recognizing that a positive antibody test with negative RNA indicates past resolved infection or false positive, not current infection 1