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Interpretive Handbook

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Test 81618 :
Hepatitis C Virus Genotype, Serum

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Unique nucleotide sequences of certain regions (ie, 5'-noncoding, core, NS5b) of the hepatitis C virus (HCV) genome allow classification of HCV into 6 major genotypes or clades (1 to 6), based on the most recently proposed HCV genotype nomenclature. In the United States, the most commonly encountered HCV genotypes are 1a and 1b, followed by genotypes 2 and 3. Worldwide geographic distribution, disease outcome and response to antiviral therapy differ among the genotypes. Therefore, reliable methods for genotype determination are important for proper selection of antiviral therapy and optimal patient management. Infections with HCV genotypes 2 and 3 have better therapeutic response rates (80%-90%) than genotypes 1 and 4 (40%-50%) to current standard combination therapy (ribavirin plus pegylated interferon alpha-2a or alpha-2b). Duration of current standard combination therapy is 24 weeks for chronic HCV genotype 2 and 3 infections in patients who show early virologic response (>2 log or 100-fold decrease in HCV RNA or no detectable HCV RNA at week 12 of therapy), while patients with chronic HCV genotype 1 and 4 infections receive a minimum of 48 weeks of combination therapy if early virologic response is achieved.


Therapeutic response rates for HCV genotype 1 infection are improved significantly (70%-80%) when a direct acting antiviral agent (eg, boceprevir, telaprevir) is added to current standard combination therapy. However, antiviral resistance can emerge during such combination therapy, and occurrence of such resistance is more frequent with HCV subtype 1a than 1b.


See Advances in the Laboratory Diagnosis of Hepatitis C (2002) in Publications.


The following algorithms are available in Special Instructions:

-Testing Algorithm for the Diagnosis of Hepatitis C
-Chronic Hepatitis C Standard-of-Care Treatment Algorithm: Combined Pegylated Interferon and Ribavirin Therapy

-Chronic Hepatitis C Treatment Algorithm: HCV Genotype 1 with Telaprevir-Containing Combination Therapy

-Chronic Hepatitis C Treatment and Monitoring Algorithm: Boceprevir-Containing Combination Therapy (HCV Genotype 1 only)

Useful For Suggests clinical disorders or settings where the test may be helpful

Determining hepatitis C virus genotype (1 to 6) to guide antiviral therapy in patients with chronic hepatitis C 


Differentiating between hepatitis C virus subtypes 1a and 1b

Interpretation Provides information to assist in interpretation of the test results

An "Undetected" result indicates the absence of detectable hepatitis C virus (HCV) RNA in the specimen.


An "Indeterminate" result has the possible following causes:

-Low HCV RNA level (ie, <1,000 IU/mL)

-Probe reactivity with multiple HCV genotypes

-Atypical viral target sequence with mismatches to PCR primers and/or probes


A genotype result of "1" without a subtype result may be due to 1 or more of the following causes:

-Low HCV RNA level (ie, <1,000 IU/mL)

-Probe reactivity with multiple genotype 1 subtypes

-An atypical genotype 1 viral target sequence


This assay is able to differentiate between HCV subtypes 1a and 1b. However, subtypes are not reported for HCV genotypes 2 to 6 due to limitations of the current genotyping assay in accurately differentiating the various subtypes of these genotypes.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

This assay should NOT be used as a screening test for hepatitis C virus (HCV) infection. It should be requested only on specimens obtained from patients confirmed to be actively infected with HCV.


An "Undetected" or "Indeterminate" HCV genotype result does not rule out active HCV infection. Test results should be correlated with routine serologic and molecular-based testing, as well as clinical presentation.


Specimens containing low HCV viral load (ie, <1,000 IU/mL) may yield "Indeterminate" results.


Known cross-reactivity between the assay probes and various HCV genotypes limits the ability of this assay to identify multiple HCV genotypes present in a given specimen. Such cross-reactivity or the actual presence of multiple HCV genotypes in the same specimen may result in an "Indeterminate" test result.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


Clinical References Provides recommendations for further in-depth reading of a clinical nature

1. Ghany MG, Strader DB, Thomas DL, et al: Diagnosis, management, and treatment of hepatitis C: an update. Hepatology 2009;49:1335-1374

2. Ghany MG, Nelson DR, Strader DB, et al: An update on treatment of genotype 1 chronic hepatitis C virus infection: 2011 practice guideline by the American Association for the Study of the Liver Diseases. Hepatology 2011;54:1433-1444

3. Germer JJ, Mandrekar JN, Bendel JL, et al: Hepatitis C virus genotypes in clinical specimens tested at a national reference testing laboratory in the United States. J Clin Microbiol 2011;49:3040-3043