Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1373 page)

   All HCV antibody–positive samples should be followed by nucleic acid testing for HCVRNA according to the testing algorithm recommended by the CDC (MMWR, May 7, 2013).

   If HCVRNA is detected, that indicates current infection. If HCVRNA is not detected, that indicates either past, resolved HCV infection or false-positive HCV antibody test.

   HCV serologic testing is not useful for detection of early/acute HCV infection, and it is not useful for differentiating between past (resolved) and chronic hepatitis C. In most infected people, antibodies will show up in blood within 6 weeks to 3 months.

   Infants born to HCV-infected mothers may have false-reactive HCV antibody test results due to transplacental passage of maternal HCV IgG antibodies. HCV antibody testing is not recommended until at least 18 months of age in these infants.

   May remain negative in immunosuppression and renal failure, although it appears to be a rare finding.

HEPATITIS C VIRUS (HCV) ANTIGEN

   Definition

   This test, based on detection of a 21-kDa protein made by a stable region of the HCV genome, may be used in research settings to aid in the diagnosis of HCV infection. It is a major component of the viral capsid. It is not clear whether it circulates freely or is only in viral particles. A commercial immunoassay to detect HCV antigen is available for research use only. Level strongly correlates with HCV RNA.

   
Normal range:
Negative.

   Use

   To predict a sustained virologic response early during therapy (4 weeks), reaching an optimal performance at month 3. The determination of total HCV core antigen levels in serum constitutes an accurate and reliable alternative to HCV RNA for monitoring and predicting treatment outcome in patients receiving PEG–interferon/ribavirin combination therapy.

   Interpretation

   Increased in hepatitis C exposure.

   Limitations