Hepatitis C tests are used to screen for and diagnose a hepatitis C virus (HCV) infection, to guide therapy and/or to monitor the treatment of an HCV infection.

An HCV antibody test is used to screen for past exposure and current infection. It detects the presence of antibodies to the virus, indicating exposure to HCV. This test cannot distinguish whether someone has an active or a previous HCV infection. There is some evidence that if the test is "weakly positive," it may be a false positive. The Centers for Disease Control and Prevention (CDC) recommends that all positive antibody tests be followed by an HCV RNA test that detects viral RNA in the blood to determine whether or not the person has an active infection.

The HCV antibody test may be performed as part of an acute viral hepatitis panel to determine which of the most common hepatitis viruses is causing a person's symptoms.

The following tests may be used to diagnose a current infection and to guide and monitor treatment:

• HCV RNA tests:
• HCV RNA test, Quantitative (HCV viral load) detects and measures the number of viral RNA particles in the blood. This test may be used to confirm the presence of the virus and diagnose an active infection. Viral load tests are also used before and during treatment to help determine response to therapy by comparing the amount of virus before and during treatment.
• HCV RNA, Qualitative is used to distinguish between a current or past infection. It is reported as a "positive" or "detected" if any HCV viral RNA is found; otherwise, the report will be "negative" or "not detected." This test is not frequently used any more.
• Viral genotyping is used to determine the kind, or genotype, of the HCV present to help guide treatment. There are 5 major types of HCV and more than 50 subtypes identified; the most common, genotype 1, accounts for about 75% of cases in the U.S. The drugs selected for treatment depend in part on the genotype of HCV infecting a person.

The CDC recommends screening for HCV infections with an HCV antibody test when people:

• Have ever injected illegal drugs
• Received a blood transfusion or organ transplant before July 1992*
• Have received clotting factor concentrates produced before 1987
• Were ever on long-term dialysis
• Are children born to HCV-positive women
• Have been exposed to the blood of someone with hepatitis C
• Are healthcare, emergency medicine, or public safety workers who had needlesticks, sharps, or mucosal exposure to HCV-positive blood
• Have evidence of chronic liver disease
• Have HIV
• Were born between 1945 and 1965, regardless of other risk factors for HCV

*The blood supply has been monitored in the U.S. since 1992, and any units of blood that test positive for HCV are rejected for use in another person. The current risk of HCV infection from transfused blood is about one case per two million transfused units.

HCV antibody testing may be done when someone has abnormal results on a liver panel, for example, or signs and symptoms associated with hepatitis. In these cases, it may be done as part of an acute hepatitis panel. Most people newly infected with HCV have no symptoms or ones that are so mild that they rarely prompt a person to visit a healthcare provider and get tested for HCV. However, about 10-20% of people may experience signs and symptoms such as fatigue, pain in the abdominal area, decreased appetite, and jaundice.

An HCV RNA test or viral load is ordered as follow-up testing when an antibody test is positive to confirm an active infection. Some laboratories will automatically perform this test if the HCV antibody test is positive.

HCV genotyping is done when a person has been diagnosed with an HCV infection and is often ordered before treatment is started to guide treatment selection.

HCV viral load testing may be ordered at the start of treatment, periodically to monitor response to treatment, and after the completion of treatment to evaluate its effectiveness.

An HCV antibody test is typically reported as "positive" or "negative."

Results of HCV viral load testing are reported as a number if virus is present. If no virus is present or if the amount of virus is too low to detect, the result is often reported as "negative" or "not detected."

Interpretation of the HCV screening and follow-up tests is shown in the table below. In general, if the HCV antibody test is positive, then the individual tested is infected or has likely been infected at some time with hepatitis C. If the HCV RNA test is positive, then the person has a current infection. If no HCV viral RNA is detected, then the person either does not have an active infection or the virus is present in very low numbers.

For monitoring purposes, an HCV viral load (HCV RNA quantitative) can indicate whether or not treatment is effective. A high or increasing viral load may be a sign that treatment is not successful whereas a low, decreasing, or undetectable viral load may imply that the treatment is working.

Successful treatment causes a decrease of 99% or more in viral load soon after starting treatment (as early as 2-4 weeks) and usually leads to undetectable viral load after treatment is completed. According to guidelines from the American Association for the Study of Liver Diseases and the Infectious Disease Society of America, an undetectable viral load in a treated person's blood 12 weeks after the end of the treatment means that the HCV infection has responded to therapy.

The results of the HCV genotype test identifies which strain of HCV the person has and helps guide the selection and the length of treatment. Treatments may differ depending on a variety of factors, including HCV genotype and the health of the person's liver (see Common Questions #5.)

HCV antibodies usually do not appear until several months after exposure but will always be present in the later stages of the disease.

About 25% of those with HIV/AIDS also have an HCV co-infection, and their liver disease is likely to progress at an accelerated rate.