Hepatitis C: An In-Depth Guide
It takes two different tests to determine whether someone has hepatitis C or not.
The first test is a screening test called the hepatitis C antibody test. It tests to see if someone has ever had hepatitis C.
The second test is a confirmatory test. It tests to see if the hepatitis C virus is currently in the body. This test is done using either the hepatitis C RNA test or the core antigen test.
Each province and territory in Canada selects the specific tests its labs use, and so testing practices vary across the country.
Hepatitis C antibody testing detects the presence of hepatitis C antibodies in the blood.
A positive result indicates the person has antibodies to hepatitis C and has been exposed to the hepatitis C virus at some point in his or her life. It does not necessarily mean that a person has hepatitis C. Approximately, 20% to 25% of people who get hepatitis C clear it without treatment. However, even after they clear the virus they will have hepatitis C antibodies for the rest of their life. It usually takes six to nine weeks for the body to make enough hepatitis C antibodies to be detectable on the test. This is known as the window period. However, it may take longer for people who have HIV to develop antibodies. In rare cases, it can take up to nine months to develop hepatitis C antibodies.
During this window period, it is possible that a person is infected with hepatitis C but will receive a negative result from the antibody test. A person who receives a negative result during the window period should be tested again after the window period has passed. This second test will provide a reliable result.
People who have a compromised immune system, such as people who have received an organ transplant or who have HIV and a low CD4 count may get a false negative test result. This means that the test says they don’t have hepatitis C antibodies but they actually do.
Currently, in Canada hepatitis C antibody testing is done on a blood sample.
Some examples of antibody tests include enzyme linked immunoassay (EIA or ELISA) and recombinant immunoblot assay (RIBA).
Hepatitis C RNA testing checks for the actual virus in the body by measuring the genetic material (RNA) of the virus in the blood.
This test is done after a person tests positive for hepatitis C antibodies. If a person also tests positive for hepatitis C RNA it means they have hepatitis C. If the test is negative it means that they do not have hepatitis C.
Another blood sample will be taken when a person returns to receive a positive hepatitis C antibody result to do the RNA test. The person will need to return for a third appointment to get the test result from the RNA test.
The RNA test can measure the concentration of virus circulating in the blood, like a viral load test (measured in IU/ml—international units per millilitre).
The tests are also used to determine the genotype or strain of the virus. This information is important when a person is thinking about starting hepatitis 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, often referred to as polymerase chain reaction (PCR) tests, are one of the most common versions of nucleic acid testing (NAT).
Hepatitis C core antigen testing checks for the core antigen, a protein that is part of the hepatitis C virus.
This test is done after a person tests positive for hepatitis C antibodies. If a person also tests positive for hepatitis C core antigen it means they have hepatitis C. If the test is negative it means that they do not have hepatitis C.
This test can be done on the same blood sample as the hepatitis C antibody test. This means that sometimes the number of visits involved in hepatitis C testing can be reduced.
One limitation of this test is that if someone has a low viral load, a person may get a negative test result when they are actually positive for hepatitis C (called a false negative result).
If a person tests positive for hepatitis C, they will need to have further tests to monitor how the virus is affecting the body. (See Monitoring tests for more information on monitoring treatment response and how the virus is affecting the body.)