How is hepatitis C diagnosed?
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. 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).