Hepatitis C virus (HCV) infection is usually diagnosed when a patient presents elevated serum alanine aminotransferase (ALT) followed by a positive anti-HCV enzyme-linked immunosorbent assay (ELISA). The diagnosis is often confirmed by a positive recombinant immunoblot assay (RIBA-3, Ortho Diagnostics). However, HCV-RNA, the only direct marker, can be detected in serum or plasma within 1-2 weeks after exposure to the virus and weeks before detectable anti-HCV antibodies or ALT increase. This makes the HCV-RNA assay an excellent confirmatory assay for initial laboratory diagnosis of infection or an adjunctive assay for an indeterminate RIBA result. This assay can detect as few as 50 viral copies per ml of serum in the patient sample, making it one of the most sensitive assay available.

In the early phase of acute infection HCV-RNA levels are at their peak and can be detected preceding or coinciding with the first ALT elevation. As anti-HCV antibody levels increase the HCV-RNA levels decrease and in 15-25% of infected individuals the disease resolves and the levels drop to undetectable levels. However, chronic infection develops in most persons (75-85%) and the clinical course is usually insidious, progressing at a slow rate without symptoms. Elevated ALT levels can be found in 60-70% of chronically infected individuals. In the remaining 30-40%, ALT levels are normal; thus a single ALT result does not rule out infection and these patients should undergo long-term follow-up. Also, since HCV-RNA levels in chronically infected individuals might be only intermittent, a single negative result for HCV-RNA does not necessarily rule out infection. From an epidemiological perspective, approximately 10-20% of chronically infected persons develop cirrhosis of the liver over a period of 20-30 years with roughly 1-4% developing hepatocellular carcinoma (HCC). In summary, this HCV-RNA assay should be preformed to aid in confirming initial diagnosis and used to help monitor patients under treatment when the HCV-RNA quantitative assay drops below 1000 viral copies per ml.

Chronic HCV infection is diagnosed by the presence of HCV RNA in the blood for at least 6 months. The quantitative determination of HCV RNA provides important information, such as baseline viral levels, Early Viral Response (EVR), End of Treatment Response (ETR), and Sustained Virological Response (SVR). Currently, the best indicator of effective treatment is SVR, which is defined as the absence of detectable HCV RNA (< 50 IU/ml) at 24 weeks after the end of treatment.