HCV Antibody Testing: Diagnosing hepatitis C begins with an antibody test. Antibodies to HCV can be detected in the blood, usually within two or three months after the virus enters the body. If a person is positive for HCV antibodies, he or she has been exposed to the virus in the past. About 15 to 25 percent of people who are initially infected with HCV are able to clear the virus from their bodies, usually within six months of exposure, so the next step is to look for the actual virus in the bloodstream, using a viral load test. If a person has an acute infection, meaning that he or she was recently infected with HCV, antibodies may not have formed yet, so a viral load is necessary to confirm infection.
HCV Viral Load Testing: A health care provider can request a qualitative HCV RNA test to determine if the virus is in a person's bloodstream. A medical provider can also order a quantitative HCV RNA test to figure out a person's HCV viral load (the amount of HCV in a measurement of blood). Various methods are used to detect HCV RNA, including TMA (transcription-mediated amplification), PCR (polymerase chain reaction), and bDNA (branched DNA). Qualitative viral load testing tends to be more sensitive than quantitative testing. Viral load testing using PCR or TMA are more sensitive than bDNA testing.
The HCV viral load is an important laboratory test. Though the HCV viral load test cannot determine if or when someone with hepatitis C will develop cirrhosis or liver failure, it can help determine the length of treatment needed. HCV viral load testing is also used during treatment to determine how well it is working.
HCV Genotypic Testing: Genotype refers to the genetic structure or makeup of living organisms. The hepatitis C virus has seven different genotypes, which are numbered in the order of their discovery. Each of these genotypes has subtypes, which were lettered in the order that they were discovered. It is important to find out which hepatitis C genotype you have, because it determines both the type of treatment and the length of treatment; HCV genotype also helps to predict the likelihood of curing HCV.
Worldwide, HCV genotype 1 is most common, accounting for 46 percent of cases. In the United States, 75 percent of all HCV infections are genotype 1; genotypes 2, 3 and 4 are less common in the United States, and other genotypes are rare. Genotype 7 was discovered in 2013 and there is only one known case. It is possible to infected with more than one HCV genotype; this is most likely among injection drug users, and people who received contaminated blood products before 1987 (when viral inactivation started), or a blood transfusion before July 1992 (when effective screening procedures were instituted).