Canadian Association for the Study of the Liver
Hepatitis C RNA testing
As with HBV DNA testing, there is a large inter-assay and intra-assay variation with HCV RNA testing. Once more the requesting physician should be familiar with the characteristics of the assay being used (table 5), and the use of a particular assay should be consistent. This variability must be considered when adapting results from the published literature to local practice.
Table 5. Manufacturer’s reported
dynamic ranges for HCV RNA assays
| Method | Working range |
| Roche AMPLICOR™ HCV Monitor™ (Quantitative) PCR Assay | 1-2x103 – 5x107 copies/ml |
| Roche AMPLICOR™ HCV (Qualitative) PCR test | 100 copies/ml (lower limit of sensitivity) |
| Chiron Quantiplex™ bDNA HCV RNA Assay version 2 | 0.2 – 120 Meq/ml (2x105 – 1.2x109 copies/ml) |
| NGI (National Genetics Institute) HCV SuperQuant™ | 100 - 5.0x107 copies/ml |
There are two types of assay for hepatitis C viral RNA. Qualitative tests give a positive or negative result. Quantitative tests give the viral concentration or viral load. The only qualitative assay available is the Roche AMPLICOR™ assay (lower limit of sensitivity 100 copies/ml). Quantitative assays available include the Chiron bDNA assay and the Roche Monitor™ assay, which measures down to 1000 particles/ml. The most recent studies on therapy using interferon and ribavirin or PEGylated interferon use the National Genetics assay, which although commercially available requires the sample to be sent to the NGI lab. There is approximately a 10-fold difference between the Monitor and the NGI assay, so that 2x106 copies/ml in the NGI assay is equivalent to about 2x105 copies/ml in the Monitor assay. This becomes important when comparing viral load data between published studies and individual patients.
Use of HCV RNA testing
Qualitative HCV-RNA testing is not essential to make the diagnosis of
hepatitis C in typical patients who
are anti-HCV positive. HCV RNA testing is indicated in patients
who are anti-HCV-positive with normal ALT levels. Interpretation
of the results of such testing is given in table 6.
Table 6 Interpretation of hepatitis
C virus RNA testing in anti-HCV-positive patients.
| ALT Concentration | HCV RNA Result | Interpretation |
|
|
|
Patient is infected, with undetectable liver disease |
|
|
|
False-positive
anti-HCV
Spontaneous viral clearance False negative HCV RNA Dormant infection with no or minimal liver disease |
|
|
|
Infected with active liver disease, |
|
|
|
False-positive
Spontaneous viral clearance False negative HCV RNA Dormant hepatitis C infection, but some other cause for liver disease |
HCV RNA testing is also sometimes necessary in patients who are immunosuppressed, and who have unexplained elevations of the aminotransferases. In these patients there may be a false-negative anti-HCV assay. Qualitative HCV RNA may also be used to determine whether infants of infected mothers are also infected, and in resolution of indeterminate serological testing. Qualitative HCV RNA monitoring is also useful in assessing the response to therapy. Quantitative HCV RNA testing is not routinely required for all patients. There was no consensus as to the requirement for quantitative HCV-RNA testing prior to treatment. Viral load is a predictor of response to therapy, but the panel felt that viral load should not be used to assess duration of therapy (see later). High viral loads should not be a deterrent to initiating treatment.