How to Better Understand Your HCV Viral Load Tests
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To everyone except physicians who treat hepatitis and fastidious researchers, the range of tests that someone with the Hepatitis C virus (HCV) endures can be dizzying. Unless you are lucky enough to have a hepatologist sit down and explain the differences and implications of each blood draw, it is easy to be misled by the barrage of lab test results. Especially important for individuals who are currently enrolled in or who have finished HCV antiviral therapy, understanding viral load tests can bring clarification to an otherwise confusing lab result.
Hepatitis C RNA tests are tools clinicians use to confirm a diagnosis and guide treatment. The challenge in discerning between the kinds of HCV tests likely lies in the similar sounding words to describe the tests: qualitative and quantitative. Even the most seasoned healthcare practitioners frequently flub these categories. Below you will find a brief description of the two HCV RNA (the genetic material for Hepatitis C) tests and a helpful mnemonic technique to differentiate between the two:
- Qualitative Test – This kind of test detects the presence or absence of HCV RNA. It is reported as either detected (positive) or not detected (negative). The qualitative test is useful to confirm an active HCV infection. The L in qualitative can be equated to a label – as in it is used to label someone as having or not having the virus.
- Quantitative Test – The quantitative test measures the actual number of copies of HCV RNA in the blood. Commonly referred to as the viral load, a quantitative test is typically used to monitor how a person is responding to HCV treatment. The N in quantitative can be equated to a number – as in it is used to report the number of HCV viral particles present.
More About Qualitative Testing
To report whether or not HCV is present in the blood, the qualitative HCV RNA tests use either a process called polymerase chain reaction (PCR) or a process called transcription-mediated amplification (TMA). If such a test is positive, or detected, then chronic Hepatitis C infection is confirmed. Although it does not compute a number, the qualitative test is more accurate than the quantitative test because it can detect very low levels of the virus.
More About Quantitative Testing
Quantitative tests that measure the actual level of Hepatitis C virus in the blood may use the processes of PCR, TMA or signal amplification (branched DNA). These viral load tests compute the number of HCV RNA particles present, and are expressed in either international units per liter (IU/L) or copies per milliliter (mL). The quantitative HCV RNA test is used to monitor individuals who undergo antiviral treatment – prior to beginning therapy, during therapy and upon its completion.
Additional Viral Load Test Facts
The following seven facts about Hepatitis C viral load tests help deepen our understanding of the testing process.
- If someone has a positive qualitative test but a quantitative test showing no detectable virus, then that person has a very low level of the virus in his or her blood.
- If someone has a negative qualitative test following antiviral treatment, they are clear of the Hepatitis C virus.
- In order to obtain a sustained viral response (considered a successful conclusion to HCV treatment), a qualitative test should be negative following the completion of treatment and then again six months later. Most physicians will use a qualitative test (as opposed to a quantitative test) to confirm a sustained viral response.
- Viral load as measured by a quantitative test does not correlate with the severity of Hepatitis C.
- The viral load measurement does not correlate with the severity of liver disease. Only a liver biopsy (or equivalent method) can determine the health of the liver.
- Because HCV viral load will normally fluctuate, repeated viral load tests are only indicated for those on or considering antiviral treatment.
- If a quantitative HCV RNA result is reported as <615 IU/L, then the test is unable to measure any of the virus. Thus, such a result should be followed by a qualitative test.
Upon reviewing the differences between quantitative and qualitative Hepatitis C tests, there will be a little less mystery in deciphering lab results. Although HCV RNA quantitative tests are mostly used to gauge how someone progresses with antiviral therapy, the qualitative test is the only way to know for sure if the Hepatitis C virus is still taking up residence in your body.
References:
http://digestive.niddk.nih.gov/ddiseases/pubs/chronichepc/#c, Chronic Hepatitis C: Current Disease Management, Retrieved July 14, 2010, National Digestive Diseases Information Clearinghouse, 2010.
http://hepatitis.about.com/od/diagnosis/f/HCVRNATest.htm, What are HCV RNA Tests?, Charles Daniel, Retrieved July 15, 2010, about.com, 2010.
http://www.hcvadvocate.org/hcsp/articles/Bernstein-1.html, The Importance of Laboratory Test Results in Hepatitis C Infection, David Bernstein, MD, FACP, FACG, Retrieved July 15, 2010, Hepatitis C Support Project, 2010.
http://www.hepatitis.va.gov/vahep?page=diag-tests-03-02, Hepatitis C RNA Qualitative Testing, Retrieved July 15, 2010, US Department of Veteran Affairs, 2010.
http://www.questdiagnostics.com/hcp/intguide/jsp/showintguidepage.jsp?fn=TG_HCV_MolecularTesting.htm, Molecular Testing in the Management of Hepatitis C Virus Infection, Retrieved July 15, 2010, Quest Diagnostics, 2010.
