Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (189 page)

   HCV RNA detection tests may be qualitative or quantitative. The most sensitive method available should be used to rule out active infection. Real-time (RT) PCR and other quantitative assays may now provide reliable quantification to levels as low as those provided by qualitative assays. An advantage of the use of quantitative HCV (viral load) assays to confirm HCV infection is that they can provide information to predict likely response to antiviral therapy and to determine response to antiviral therapy. Even though HCV RNA assays are calibrated to an international standard, results may vary across different assays. Therefore, the use of a single assay is recommended for serial testing of a patient’s HCV viral load.

   Anti-HCV positive (confirmed), HCV RNA negative: Resolved HCV infection.

   Anti-HCV positive (confirmed), HCV RNA positive: Active HCV infection.

   
HCV genotype analysis
: HCV genotype should be determined for patients with acute or chronic HCV infection. There are six different HCV genotypes and many subtypes. The prevalence of different genotypes shows geographic variability; genotype 1 is most common in the United States.

   There are genotype-specific differences in response to therapy; the HCV genotype is a factor used to determine the dose and duration of antiviral treatment for chronic HCV infection. Genotypes 2 and 3 have better response rates than genotypes 1 and 4.

   
Laboratory testing in chronic HCV infection
: A number of medical conditions may impact the severity of chronic HCV infection and affect response to treatment. In addition, chronic HCV infection may have disease manifestations outside the liver. In addition to
HCV viral load
testing, tests to evaluate patients for treatment and to monitor response to therapy include the following:

   Testing to rule out other chronic diseases, including
infection
(like HIV, hepatitis A, and hepatitis B),
genetic condition
(like hemochromatosis, Wilson disease, α
₁
-antitrypsin deficiency), or
autoimmune disease
(like positive reactions for ANA, AMA, or antiactin antibody).

   A patient
IL28B genotype
predicts a more favorable response to therapy.

   
Hepatic function panel
: Serum aminotransferase levels typically increase within 2–8 weeks after infection but commonly show significant variability and may return to almost-normal levels (formerly called
acute “relapsing” hepatitis
). The degree of ALT elevation is an unreliable predictor of histology in HCV infection; biopsy is needed to define the severity of liver damage. Abnormal bilirubin and alkaline phosphatase levels suggest a cholestatic process.

   
CBC and PT.

   Metabolic assessment: including
renal
and
thyroid function panels
and
25-hydroxy-vitamin D3 level.