What is the Difference between Viral Load Testing and Antibody Testing? Part 2
Viral load testing detects the amount of hepatitis C virus that is found in the blood. Viral load testing is also referred to as HCV RNA testing. The RNA refers to the genetic material of the virus, which this test detects. Results are expressed as International Units (IU) per mL or L of blood (IU/mL or IU/L). In people with a reactive antibody test, the HCV RNA test confirms infection with hepatitis C.
Viremia is another term for the amount of virus in the blood. The test can be interpreted as follows:
- High Viral Load: This is defined as viral load greater than 800,000 IU/mL
- Low Viral Load: This is defined as viral load less than 800,000 IU/mL
- Undetected or No HCV: This is defined as viral load less than 15 IU/mL - this does not necessarily rule out a diagnosis of hepatitis C; it occasionally occurs when test can not detect low viral levels
Viral load testing does not tell us:
- The severity of the hepatitis C infection (i.e., whether fibrosis is present)
- Length of time of infection
- Mode of infection
- Which treatment would be best to initiate
Repeating the test after treatment
Response to treatment is assessed by checking the viral load during treatment and at 12 weeks following the cessation of therapy. The goal is to see the viral load go down during treatment. A sustained virologic response (SVR) is the term used to indicate treatment success. It is defined as "aviremia 24 weeks after completion of antiviral therapy."2 Unlike the antibody test where detectable antibody levels will be maintained after treatment, successful treatment will show undetectable viral loads.
Putting antibody testing and viral load testing together
Viral load testing and antibody testing go hand-in-hand; However, each test captures a very different picture of hepatitis C. Taken together, the plausible outcomes of both tests include:
- Antibody Non-Reactive - This can be interpreted that no antibodies to the hepatitis C virus have been detected. There has been no exposure to the hepatitis C virus. Unless the person falls in one of the groups mentioned in part 1 (immunocompromised, on dialysis, has HIV infection, or may have been exposed to the virus within the past 6 months), no further action is taken.
- Antibody reactive & viral RNA detected - This indicates that there is a current, active infection. There are various effective anti-virals available that can be trialled. The next step is a discussion with the clinician outlining preferences to treatment.
- Antibody reactive & no viral RNA detected - This indicates that there is no current infection. In people who have not been treated, this can occur if the individual was able to clear the virus himself/herself naturally. In those who have been treated, this indicates positive response to treatment, or an SVR.
Understanding the differences between antibody and viral load testing can help equip people with the knowledge to work through their diagnosis with their clinicians. For some people, understanding the diagnosis is a powerful tool in the journey towards mitigating fear and gaining confidence.
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