Viral Load Testing
An important way to diagnose the hepatitis C virus (HCV) is viral load testing. Viral load testing can also be helpful in monitoring treatment response. And it is used to determine if a person is cured of HCV.1-3
What does the viral load test measure?
A viral load test looks for active HCV in the blood. Specifically, it looks for HCV RNA.
RNA is a type of genetic material. Just like we have DNA in our genes, HCV has RNA. This RNA is what HCV uses to replicate in the body. A person who has HCV RNA in their blood has active HCV. A person who does not have HCV RNA does not have active HCV.1,2
Results of viral load testing
There are several different tests to look for HCV RNA. It is common to have a quantitative test. This is a test that gives a specific number of HCV RNA copies in the blood. Viral load is usually listed in copies per milliliter of blood or international units per milliliter (IU/mL).1-3
There can be a wide range of quantitative viral load results. Viral load can be as high as several million or it can be a couple thousand. If HCV RNA is not found on viral load testing, the result is undetectable. Undetectable may mean there is no virus at all or that there is just too little to be detected on the test.1-3
There are also qualitative viral load tests. These just detect if HCV RNA is present or absent. Knowing whether HCV RNA is present is helpful in diagnosis. However, quantitative tests are often used to monitor treatment response.3
When are viral load tests used?
Viral load tests are used in several situations. Usually, a person is first screened for HCV with an antibody test. An antibody test looks for a protein the body has made specifically to fight off HCV.
Someone who has a positive antibody test may currently have HCV or may have had it in the past. In order to separate these 2 possibilities, an HCV viral load test can be helpful.
A person who has a positive antibody test and a positive viral load have active HCV.1-3
Viral load testing can also be used to see if a person is responding to treatment. For example, if a person starts a direct-acting antiviral drug (DAA) and their viral load starts going down, the drug is working.
Viral load testing can also be used to determine if a person is cured of HCV. HCV is considered cured if the viral load remains undetectable for 10 to 12 weeks after treatment. This is called sustained virologic response (SVR).1
Viral load testing can also be used to determine if someone who has had HCV in the past has become reinfected. Antibody tests are not helpful for people who have been exposed to HCV in the past, because they will always be positive. This is where viral load testing for HCV RNA can be useful.4
Is a high viral load bad?
Viral load test results can change over time. They can change even if a person is not on treatment. They do not predict how a person’s HCV will behave. For example, a higher viral load does not mean a person has more severe HCV or has more severe damage to their liver. There are other tests, like blood tests or imaging, that look for severe damage or complications of HCV.1-3
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