Hepatitis C Virus Antibodies

Each of the five most common tests has a slightly different purpose:   

• Anti-HCV tests detect the presence of antibodies to the virus, indicating exposure to HCV. These tests cannot tell if you still have an active viral infection, only that you were exposed to the virus in the past. Usually, the test is reported as “positive” or “negative.” There is some evidence that, if your test is “weakly positive,” it may not mean that you have been exposed to the HCV virus.
• HCV RIBA test is an additional test to detect the presence of antibodies to the virus. It can tell if the positive anti-HCV test was due to exposure to HCV or represents a false signal. "Weakly positive" anti-HCV tests can be re-tested with HCV RIBA to see if they are positive or not. Like the anti-HCV test, the RIBA test cannot tell if you are currently infected, only that you have been exposed to the virus. 
• HCV-RNA test identifies whether the virus is in your blood, indicating that you have an active infection with HCV. It is usually performed by a test called a qualitative HCV; the result is reported as a “positive” or virus “detected” if any virus is found; otherwise, the report will be “negative” or “not detected” if no virus is found. The test is also used after treatment to see if the virus has been eliminated from the body. 
• Viral Load or Quantitative HCV tests measure the number of viral particles in your blood. Viral load tests are often used before treatment to help determine how long treatment needs to be given (along with other factors, such as your age, gender, the changes seen in a liver biopsy, and genotype, discussed below). With newer forms of treatment, it is also used to follow response to treatment by comparing the amount of virus before and after treatment (usually after 3 months). 
• Viral genotyping is used to determine the kind, or genotype, of the virus present; there are 6 major types of HCV; the most common (genotype 1) is less likely to respond to treatment than genotypes 2 or 3 and usually requires longer therapy. Genotyping is often ordered before treatment is started to give an idea of the likelihood of success and how long treatment may be needed.

Hepatitis C infection is a common cause of chronic liver disease . About 75-85% of those infected develop chronic hepatitis, and about 20% of those develop cirrhosis. HCV testing is recommended in the following cases: 

• If you have ever injected illegal drugs 
• If you received a blood transfusion or organ transplantation before mid-1992* 
• If you have received clotting factor concentrates produced before 1987 
• If you were ever on long-term dialysis 
• For children born to HCV-positive women 
• For health care, emergency medicine, and public safety workers after needlesticks, sharps, or mucosal exposure to HCV-positive blood 
• For people with evidence of chronic liver disease

* The blood supply has been monitored in the UK since mid-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 less than 1 case per million transfused units.

A positive anti-HCV test may be confirmed with an HCV RIBA test, especially if the test is “weakly positive.” Qualitative HCV-RNA is often used when the antibody test is positive to see if the infection is still present. HCV viral load and genotyping may be done to plan treatment; viral load and qualitative HCV RNA are also used to monitor response to treatment.

If the antibody test result is positive, you have probably been infected with hepatitis C, even if it was so mild you did not realize you had it.

A positive RIBA confirms that you had been exposed to the virus, while a negative RIBA indicates that your first test was probably a false positive and you have never been infected by HCV.

A positive (or detectable) HCV RNA means that you are currently infected by HCV.

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

Ten percent of people with HCV have no recognized source for their infection. Sexual exposures account for 15% of HCV cases.