Types of tests - Diagnostic tests
A diagnosis of Hep C infection is not possible with a single test. Some tests are designed to be diagnostic tests to determine if a person has ever been infected with the hepatitis C virus (HCV), while others are used to monitor the status of the virus once a person has been diagnosed with HCV. These other tests are also used to monitor a person’s response to treatment. Further tests monitor how the virus is affecting the body. (See Types of tests – Monitoring tests for more information on monitoring treatment response and how the virus is affecting the body.)
New tests are being developed to make the testing process faster and more accurate, but each province or territory in Canada selects the specific tests its labs will use, so there are differences across the country. Informed consent is an important part of the testing process.
1. HCV antibody testing: These tests detect the presence of hepatitis C antibodies in the blood. A positive result indicates the person has antibodies to HCV and therefore has been exposed to the hepatitis C virus at some point in his or her life. However, the full status of hepatitis C infection cannot be known based on antibody testing alone. The person may have an active infection, meaning he or she has virus circulating in the body and are infectious, or an inactive infection, which means he or she has cleared the virus. It usually takes 6-9 weeks (but can take up to six months) after HCV infection for the body to make enough antibodies for the test to give a positive result. This time period is known as the window period. Some examples of antibody tests include enzyme linked immunoassay (EIA or ELISA) and recombinant immunoblot assay (RIBA).
Screening for Hep C is recommended for all people diagnosed with HIV. Having advanced, untreated HIV can sometimes lead to false negative results in Hep C antibody tests because the immune suppression caused by HIV reduces the body’s ability to manufacture antibodies. More tests may be required to get the full understanding of the status of HCV in the body.
2. RNA testing: These tests check for the genetic material of the virus (RNA) in the blood. They are generally used when a person has tested positive for HCV antibodies. They can measure the concentration of circulating virus in the blood, like a viral load test (measured in IU/ml—international units per millilitre). This is important because some people are able to clear the HCV from their body without treatment and thus will have no detectable HCV RNA in their blood. The tests are also used to determine the genotype of the virus. This information is important when a person is thinking about starting Hep C treatment because some genotypes of the virus respond better to treatment than others.
Some provinces use two versions of these tests—a quantitative one to count the amount of virus in the blood and a qualitative one to measure if the virus is detectable or undetectable. Tests for detecting RNA in blood samples are often referred to as polymerase chain reaction (PCR) tests and are one of the most common versions of nucleic acid testing (NAT).