The following assays are used for diagnosing and managing Hepatitis C (HCV) infection:
Serologic assays: These detect a specific antibody to the hepatitis C virus (anti-HCV) in the serum or plasma and are reported as a positive or a negative value
Molecular assays: These detect viral nucleic acid and can be qualitative or quantitative. Quantification of the virus is reported using international units per milliliter (IU/mL).
Genotyping assays: These are most useful in epidemiological studies and are clinically used to predict the likelihood of response and duration of therapy; they help to classify the virus into the 6 major genotypes. 
These tests detect antibodies to HCV (anti-HCV) and are used for screening and diagnosing HCV infection. Results are reported as anti-HCV positive or negative values. Three different assays are approved by the US Food and Drug Administration (FDA) for clinical use, Abbott HCV enzyme immunoassay (EIA) 2.0 (Abbott laboratories), ORTHO HCV version 3.0 enzyme-linked immunoassay (ELISA) (Ortho-Clinical Diagnostics) and VITROS Anti-HCV assay (Ortho-Clinical Diagnostics). These tests have very high sensitivity and specificity for HCV detection (sensitivity of greater than 99%, specificity of 99% in immunocompetent patients).
A negative test is sufficient to exclude a diagnosis of chronic HCV infection in immune-competent patients. Those on hemodialysis and patients with immune deficiencies may have false-negative results, whereas false-positives may occur in patients with autoimmune disorders. [1, 2]
These tests are FDA approved for detection of HCV RNA; they can be qualitative (ie, Amplicor HCV v2.0, CobasAmplicorHCV v2.0, Ampliscreen, Versant HCV RNA, Procleix HIV-1/HCV Assay) or quantitative (ie, Amplicor HCV Monitor, CobasAmplicor HCV monitor v2.0, Versant HCV RNA 3.0 assay, CobasTaqman HCV test).
Qualitative tests only detect the presence of HCV RNA (specificity, approximately 98%) whereas the quantitative assays detect the viral load in IU/mL (specificity, approximately 98-99%) and provide adequate information that guides clinicians to manage and monitor treatment outcome. [1, 3]
Both types of assays in association with the clinical presentation (jaundice, ALT elevation) have been used to adequate identify acute or chronic HCV infections. After an acute HCV infection, HCV RNA could be detectable in serum within 2 weeks following exposure. On the other hand, anti-HCV could take about 8-12 weeks before results are positive. Both test results are positive in case of acute or chronic infection.
However, anti-HCV positivity with nondetectable HCV RNA could be seen in cases of acute infection during a period of viral clearance and false positives may result; this may also occur after recovery from infection or following spontaneous resolution of HCV infection. On the other hand, HCV RNA results can be positive with negative anti-HCV findings in cases of early stages of acute infection, false positive results, or chronic infection in an immunosuppressed individual. 
Collection and Panels
Obtain 3.5 mL of blood in a gold top tube (serum separator tube), a plain red top tube, or serum separator microtainer. The patient does not need special preparation. The specimen is allowed to clot; it should be centrifuged and refrigerated or frozen for transport and stabilization.
For HCV RNA polymerase chain reaction (PCR) testing in adults, 4-6 mL of blood should be collected into an EDTA (purple-top) tube. In infants, 2 mL of blood is collected into a pediatric EDTA (purple-top) tube. In newborns, a full purple/lavender-top microtainer tube should be obtained.
Following collection, the specimen must be immediately brought to the laboratory for processing. The patient does not need any special preparation. In the laboratory, the plasma is separated from whole blood within 6 hours of collection by centrifugation at room temperature.
For HCV genotyping, 6 mL of patient’s blood sample is collected in an EDTA tube. The plasma must be separated and frozen within 4 hours of collection; it is centrifuged and must be frozen for transport and stabilizing.
Hepatitis C virus (HCV) infection is the most common chronic bloodborne infection in the United States; it is also one of the leading known causes of liver disease in the United States. 
Approximately, 180 million people are infected worldwide with HCV, in the United States; the infection prevalence is estimated to be around 4 million people, with an estimated of 17000 new infections in 2010. Infection with HCV is a common cause of both acute and chronic liver disease; it is frequently a silent disease with few clinical manifestations; however, chronic hepatitis C is a common cause of cirrhosis, end-stage liver disease, and hepatocellular carcinoma. In the United States, it is the single major cause of chronic liver disease hence the principal reason for liver transplantation in adults. 
Hepatits C virus is a single-stranded positive-sense RNA virus; it is classified in the family of Flaviviridae on hepacivirus genus. Six major genotypes have been identified. 
The diagnosis acute of hepatitis C is suggested by the presence of clinical or biochemical evidence of acute hepatitis accompanied by anti-HCV and/or HCV RNA in serum. In most cases, the diagnosis can be made based on anti-HCV testing alone but sometimes it requires repeat testing for HCV antibody 4-6 weeks later or direct assays for HCV RNA. Neither anti-HCV or HCV RNA testing can reliably distinguish between acute and chronic HCV with a superimposed form of acute liver injury or an acute exacerbation. 
Approximately, 55-85% of patients who develop acute HCV remain infected. The diagnosis of chronic HCV is generally made on the basis of persistent ALT elevations or HCV RNA in serum for 6 months or longer. These patients are at risk of progression to cirrhosis and/or hepatocelullar carcinoma; this progression is accelerated in patients of older age, who are obese, who have HIV, or who abuse alcohol. 
Appropriate screening at diagnosis can correctly identify appropriate candidates for HCV treatment with peginterferon alfa and ribavirin, preventing complications and death from HCV infection. 
The American Association for The Study of Liver Disease (AASLD) recommends screening in high-risk groups including intravenous illicit drug abuse, intranasal drug users who share paraphernalia, individuals who have received a blood component transfusion or organ transplant before 1992, hemophiliacs who have received blood products before 1987, unexplained elevations of aminotransferase levels (AST/ALT), patients ever on hemodialysis, children born to HCV-infected mothers, those with HIV, health care and other workers after a needle stick injury or mucosal exposure to HCV-positive blood, and current sexual partners of individuals with HCV infection.