Hepatitis C 101: What Does Viral Load Mean?
When someone is tested for hepatitis C (HCV), they are usually tested with an antibody test. If a hepatitis C antibody test result is negative, the person does not have HCV. The only exception to this is if the person was recently exposed, then their body might not have developed antibodies yet. In that case, the individual will need to return for subsequent testing in 3-6 months.
However, if the antibody test comes back with a positive result, then it means the person *might* have hepatitis C. At that point, the practitioner usually requests another test called a hepatitis C viral load test, or an HCV RNA test, which tests for the hepatitis C virus in a person’s blood to determine if the individual actually has HCV.
According to the CDC, approximately 15%–25% of people who are infected with hepatitis C are able to clear the virus on their own. This means they have the antibodies to the hepatitis C virus – they have been exposed – but they don’t actually have HCV.
The viral load test is used to make a diagnosis of hepatitis C, and then it is used again when a person is undergoing treatment for HCV.
What Is Viral Load?
Viral load is the amount of viral particles present in the blood stream, as detected by the proteins or building blocks of the virus, the RNA. RNA tests measure extremely small quantities of the hepatitis C virus to determine the number of viral particles per milliliter of blood.
Viral load helps determine if treatment will be successful – the lower the viral load, the more likely one is to have a successful treatment. Viral load, however, does not determine the risk of damage to someone’s liver or what type of symptoms someone will experience.
How is Viral Load Reported?
Viral load can be reported by laboratories as copies per milliliter or international units (IU) per milliliter. Most labs have moved to using international units per milliliter, because it standardizes reporting of test results between different labs and countries.
What Is a High and Low Viral Load?
A high viral load is considered to be anything over 800,000 IU/ml (800,000 International Units per milliliter of blood or 800,000 standardized units per milliliter) or 2 million copies/ml. A low viral load is, typically, anything less than that, although some studies have shown that the cutoff is too high and should be readjusted to indicate that those with a viral load of 400,000 IU/ml or lower are thought to respond best to treatment.
It’s important to understand that, even though viral load is measured when a person tests positive for HCV antibodies and then again at regular intervals while they are undergoing treatment for HCV (usually, every 3 months), viral load is only a measurement of the potential for successful therapy and then whether or not therapy was successful. Other tests – liver biopsies and enzyme tests or genotyping one’s virus will determine the extent of the disease’s damage to the liver and how fast the disease will progress.
Unlike other infections where viral load can affect a patient’s prognosis, a low HCV viral load only means a patient is likely to respond well to treatment, and a high viral load only means there is lower chance of successful treatment.
Can I Have Hepatitis C Without a Measurable Viral Load?
It’s possible to test positive for HCV antibodies and then test negative for HCV with a viral load test. Sometimes, the hepatitis C virus is undetectable, because an individual has cleared the virus on their own, or the viral load in the blood stream has gone down temporarily.
Over time, the body’s viral load goes up and down. If someone tests positive for HCV antibodies and negative for the HCV virus, a practitioner will usually have them test again in 3-6 months to ensure they do not have an HCV infection.
If someone previously had a measurable viral load and no longer does, that means that treatment was successful, and the individual is in remission. A person who is in remission will still have HCV antibodies, but their viral load will no longer be detectable, and if their viral load remains undetectable that indicates they’ve recovered from the infection.
How Does Viral Load Determine if Treatment Worked?
To determine if treatment is working, practitioners use logarithms or factors.
For instance, if a person with HCV has a viral load of 800,000 upon beginning treatment, and 3 months later has a viral load of 400,000, viral load has lowered by a factor of 2, which isn’t considered a significant change. Whereas, were that same patient’s viral load to change from 800,000 to 8,000, viral load would have dropped by a factor of 100.
To be considered a significant drop, indicating that treatment is working, viral load has to drop by a factor of 100 or more. Anything less usually indicates that treatment is not going to be successful.
Is Someone Cured when Viral Load is No Longer Detectable?
After treatment, if a patient’s viral load remains undetectable, it is said that they have a sustained virologic response (SVR). In order to have an SVR, a patient must have a 50 IU/mL to undetectable viral load tested with a PCR test for at least 6 months upon completion of treatment.
At which point, practitioners will say the patient is in remission and/or has an SVR, meaning that they are 98% certain they are cured of the virus. In rare cases, a person can relapse a year or two after treatment, and subsequent testing is necessary to ensure that hasn’t occurred.1-4
- Hepatitis C. National Institutes of Health: 2013.
- Hepatitis C: Frequently Asked Questions. U.S. Department of Veterans Affairs: 2013.
- Hepatitis C FAQs for the Public. Centers for Disease Control and Prevention: 2015.
- When and in Whom to Initiate HCV Therapy. American Association for the Study of Liver Diseases and Infectious Disease Society of America.