What is a Viral Load for Hepatitis C?

Measuring viral activity tells us how effectively a treatment is working

Electron micrograph of hepatitis C virion (HCV). Photo Credit: BSIP/UIG/Getty Images

A viral load is simply the measurement of the amount of virus in your blood. Viral load measurements are commonly used to monitor chronic viral diseases such as HIV, hepatitis B (HBV), and hepatitis C (HCV).

In the case of HCV, a test called a quantitative HCV RNA assay is used to measure the virus's genetic material (RNA) detected in a milliliter of blood. Other technologies can be also used to monitor viral activity, most of which do so by detecting either viral DNA or RNA.

Why is a Viral Load Important?

Doctors use your viral load to determine how well you're responding to anti-viral treatment. Typically your viral load will be tested before you start therapy (for hepatitis C, for instance) and then repeated periodically to measure how you are responding. At least two viral load results are needed to assess treatment efficacy.

A significantly reduced viral load, like a 100-fold decrease in viral actively, generally means that treatment is working. Ideally, a person would achieve a so-called "undetectable" viral load, meaning that the current testing technologies are unable to find any evidence of the virus in blood samples.

It's important to understand that while the test is valuable in predicting treatment outcomes, it does not tell you anything about the severity of your liver disease. Typically, liver biopsies and imaging tests (for example, ultrasound or MRI) are needed for that.

High Versus Low Viral Load

Insofar as viral hepatitis C is concerned, a high viral load is usually over 800,000 IU/L, while a low viral load is under 800,000 IU/L. This range can vary significantly, however, based on what is considered average in a specific region or population.

It's important to note, however, that a viral load of 800,000 IU/L does not mean you have 800,000 actual viruses in your blood.

Rather, it means that the lab has determined there are 800,000 international units (IU) in a liter of blood. An IU is a standard measurement used by pathologists to ensure consistency from lab to lab and is considered more accurate than a simple "head count" of viral RNA.

Typically speaking, though, 800,000 IU/L correlates to around two million copies of viral RNA. 

What An Undetectable Viral Load Means

The period of remission (undetectable viral load) 12 weeks after completing hepatitis C therapy is known as a sustained virologic response (SVR), or SVR12. Nearly all people who achieve an SVR12 go on to achieve an SVR24, which means there has been no viral activity detected 24 weeks after treatment.

An undetectable viral load does not necessarily mean you have no virus in your blood or that you've achieved a cure. However, if you are able to sustain an undetectable viral load for a period of 24 weeks (and now experts think even just 12 weeks) the likelihood of the virus reappearing (rebounding) is consider extremely low. In fact, in this instance, a person is technically considered to be cured.

While tests can vary in terms of sensitivity, which means their ability to detect the virus, most current assays are extremely accurate.

A Word From Verywell

While the tests involved in diagnosing and treating hepatitis C may seem complex, try not to get too bogged down in the details. If you do have hepatitis C, remain active in your liver health by seeing a doctor who has experience treating people with hepatitis C.

Take your medications as instructed and remain in close contact with your doctor. With proper care, the good news is that you can clear the virus from your body (and essentially be "cured").

Sources:

Burgess SV, Hussaini T, Yoshida EM. Concordance of sustained virologic response at weeks 4, 12 and 24 post-treatment of hepatitis c in the era of new oral direct-acting antivirals: A concise review. Ann Hepatol. 2016 Mar-Apr;15(2):154-9.

Gupta E., Bajpai M, Choudhary A. Hepatitis C virus: Screening, diagnosis, and interpretation of laboratory assays. Asian J Transfus Sci. 2014 Jan-Jun;8(1):19-25.

University of Washington. Hepatitis C Online: Goals for treatment and predicting response

U.S. Department of Veterans Affairs. Viral Hepatitis: Hepatitis C RNA quantitative testing.

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