Hepatitis C laboratory tests
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Hepatitis C |
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Diagnosis |
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Treatment |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-In-Chief: Yazan Daaboul; Serge Korjian
Overview
The laboratory diagnosis of hepatitis C infection is first by documenting positive serologies (Anti-HCV antibodies) followed by HCV RNA quantification by PCR to determine the viral load and differentiate chronic infection from remission.
Diagnosis
The diagnosis of HCV is rarely made during the acute phase given that the majority of people infected are asymptomatic during this phase of the disease. Chronic hepatitis C may be suspected on the basis of the medical history (particularly if there is history of IV drug abuse or inhaled substance usage such as cocaine), a history of piercings or tattoos, unexplained symptoms, or abnormal liver enzymes or liver function tests found during routine blood testing.
Hepatitis C testing begins with serological blood tests used to detect antibodies to HCV. Anti-HCV antibodies can be detected in 80% of patients within 15 weeks after exposure, in >90% within 5 months after exposure, and in >97% by 6 months after exposure. Overall, HCV antibody tests have a strong positive predictive value for exposure to the hepatitis C virus, but may miss patients who have not had seroconversion, or have an insufficient levels of antibodies to detect.
Anti-HCV antibodies indicate exposure to the virus, but cannot determine if ongoing infection is present. All persons with positive anti-HCV antibody tests must undergo HCV RNA PCR quantification to determine the viral laod. The HCV viral load is an important factor in determining the probability of response to interferon-based therapy, but does not indicate disease severity nor the likelihood of disease progression.
In people with confirmed HCV infection, genotype testing is generally recommended. There are six major genotypes of the hepatitis C virus, which are indicated numerically (e.g., genotype 1, genotype 2, etc.). HCV genotype testing is used to determine the required length and potential response to interferon-based therapy.
Laboratory Diagnosis
- HCV Enzyme-linked immunosorbent assay (ELISA)
- Positive within 4-10 weeks after infection
- False negatives can occur with HIV infection, chronic renal failure, cryos
- HCV RNA
- Polymerase chain reaction (PCR) highly sensitive for confirming viremia
- Predicts response to therapy but not risk of progression
A single positive PCR test indicates infection with HCV. Negative tests require retesting especially in cases with high clinical suspicion.
Follow-up testing for health care personnel exposed to HCV-positive blood
- For the source, perform baseline testing for anti-HCV.
- For the person exposed to an HCV-positive source, perform baseline and follow-up testing, including
- baseline testing for anti-HCV and ALT activity AND
- follow-up testing for anti-HCV (e.g., at 4–6 months) and ALT activity. If earlier diagnosis of HCV infection is desired, testing for HCV RNA may be performed at 4–6 weeks.
- Confirmation by supplemental anti-HCV testing of all anti-HCV results reported as positive by enzyme immunoassay.