Blood tests for hepatitis C
There are several blood tests for the diagnosis of hepatitis C infection. Blood can be tested for antibody to hepatitis C (anti-HCV antibody). It takes up to six months for antibodies to develop after the initial infection with hepatitis C, so screening for antibodies may miss a few newly-infected individuals. Having antibodies is not an absolute indication of active, multiplying hepatitis C virus, but if the antibody test is positive (antibody is present), the statistical probability of active infection is greater than 99%.
Several tests are available to measure the amount of hepatitis C virus in a person's blood (the viral load). The hepatitis C virus's RNA can be identified by a type of test called polymerase chain reaction (PCR) that detects circulating virus in the blood as early as 2-3 weeks after infection, so it can be used to detect suspected acute infection with hepatitis C early infection. It also is used to determine whether active hepatitis is present in someone who has antibodies to hepatitis C, and to follow the viral load during treatment.
Blood tests are also performed to identify the genotypes of HCV. Genotypes respond differently to different treatment, so this information is important in selection of the most appropriate treatment regimen.
Estimation of liver fibrosis using blood tests also is quite reliable in diagnosing clinically significant scarring; these include FIB-4, FibroSure, Fibrotest, and aspartate aminotransferase-to-platelet ratio index (APRI).
Liver biopsy and non-invasive tests for hepatitis C
The next step is to determine the level of liver scarring that has occurred. Liver biopsy allows examination of a small sample of liver tissue under a microscope, however, liver biopsy is an invasive test, and has significant risks of bleeding. It also might miss abnormal areas in early disease.
Non-invasive tests have largely replaced liver biopsy except in special situations. Liver stiffness indicates that advanced liver scarring or cirrhosis may be present. Transient elastography may be used to measure this stiffness by ultrasound or magnetic resonance imaging (MRI).
Pre-treatment evaluation for hepatitis C also should include:
- Testing for HIV
- Testing for antibodies to hepatitis B and hepatitis A and vaccination if antibodies are not present
- If past or current hepatitis B infection is detected, it may need to be treated at the same time. There are reports of hepatitis B that reactivated or progressed to serious liver failure or death in some patients who were treated only for hepatitis C. This has been reported to occur during or even after HCV treatment.
- Recommending abstinence from alcohol use
- Counseling about measures to prevent the spread of hepatitis C and HIV
- If cirrhosis is present, vaccination against pneumococcal infection, regardless of age.