Hepatitis C virus (HCV) is a bloodborne infection that is one of the leading causes of liver disease. If left untreated, HCV can lead to cirrhosis, hepatocellular carcinoma, and death. The current standard of care for HCV is a combination of pegylated-interferon (peg-IFN) and ribavirin (RBV) in which the goal of treatment is to decrease complications and death due to HCV. HCV displays genetic polymorphism, where patients with HCV genotype 1 may have higher viral replication rates and are less likely to respond to treatment. These patients require a longer duration of treatment and a higher RBV dose. The interleukin (IL) 28B genotype test is associated with a sustained virologic response (SVR), defined as an undetectable HCV ribonucleic acid (RNA) upon completion of treatment and 24 weeks thereafter.
The IL28B genotype test can be used to predict response to peg-IFN and RBV in HCV genotype 1 patients. The test result indicates whether the patient has an IL28B CC, CT, or TT genotype. Patients who have the IL28B CC genotype are more likely to have a SVR with peg-IFN and RBV treatment, whereas patients who have the TT genotype are more likely to be nonresponders. This information can help clinicians and patients make informed decisions on how to best manage their HCV infection.
The IL28B polymorphism test is a polymerase chain reaction (PCR) analysis of a single nucleotide polymorphism (SNP) (rs12979860 C/T) on chromosome 19q13.  The test requires either whole blood or buccal swab.
Public Health Importance
Chronic liver disease is the tenth leading cause of death in the United States. The Center for Disease Control and Prevention (CDC) estimates that 40% of chronic liver disease is caused by HCV.  Treatment of HCV can reduce the risk of developing cirrhosis, hepatocellular carcinoma, and death. Treatment also prevents person-to-person transmission. However, SVR does not occur in all patients. Two clinical trials have showed that only 41% and 46% of patients with HCV genotype 1 achieved SVR with peg-IFN and RBV.  In addition, many patients do not complete treatment due to adverse events that are associated with peg-IFN and RBV.  Selecting appropriate and motivated patients to treat is important. The IL28B genotype test may aid healthcare providers and patients when making decisions on whether or not to start therapy in HCV genotype 1 patients.
Published Reviews, Recommendations and Guidelines
Systematic evidence reviews
Recommendations by independent group
Guidelines by professional groups
PubMed and Cochrane Review searches were conducted using a combination of the following keywords: IL28 polymorphism genotyping, hepatitis C virus, interferon, and ribavirin. The results were limited to English, and yielded a total of nine relevant articles.
Analytic Validity No information regarding the analytical validity of the IL28B genotype test was available in either the primary literature or on the LabCorp website. 
Christine M. Nguyen and Margaret Mendes are funded by the Veterans Affairs San Diego Healthcare System. Shirley Tsunoda and Joseph D. Ma are funded by the University of California, San Diego Skaggs School of Pharmacy and Pharmaceutical Sciences.
The authors have declared that no competing interests exist.
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- dbSNP website. Available at: http://www.ncbi.nlm.nih.gov/sites/entrez?db=snp&cmd=search&term=rs8099917. Accessed on 14 Nov 2010.