Qualitative Detection HCV Assays

There are currently two FDA-cleared qualitative HCV RNA test kits available for diagnostic use, the Amplicor HCV test v2.0 (Roche) and the Versant HCV RNA qualitative test (Bayer).

The Amplicor HCV test v2.0 is based on RT-PCR amplification of a portion of the 5' UTR and has an analytical sensitivity of 50IU/ml.65 The test incorporates an internal control to detect PCR inhibitors and deoxyuridine triphosphate (dUTP) and uracil-N-glycosylase in the reaction mixture to prevent false positives due to amplicon carryover. The test is available in two formats, a manual microwell plate assay and a semiautomated assay designed for the COBAS instrument. The performance characteristics of the Amplicor HCV tests are well established66 and are the most commonly used qualitative HCV RNA tests in clinical laboratories participating in the proficiency-testing surveys of the College of American Pathologists.

The Versant HCV RNA qualitative test also targets the 5' UTR but uses TMA to amplify the targeted region. The analytical sensitivity of the Versant HCV RNA assay is 5 IU/ml. The increase in analytical sensitivity over the Amplicor tests is due in part to the larger sample volume (500 |l versus 200 |l) and the use of a specific target capture step to isolate HCV RNA rather than total RNA precipitation. This test also employs an internal control RNA to detect the presence of amplification inhibitors.

The Versant HCV RNA assay can detect residual serum HCV RNA in some patients with no detectable HCV RNA as determined by the Amplicor v2.0 assay at the end of treatment with IFN and subsequently experienced virolog-ical relapse.67,68 However, this difference was not observed with end-of-treatment samples from patients treated with pegylated IFN.69 The two qualitative HCV RNA assays demonstrated excellent concordance in a study designed to

Table 37-4. Commercially Available HCV RNA Tests

Lower Limit of

Test Kit

Method

Manufacturer

Detection (IU/ml)

Dynamic Range

Clinical Application

Qualitative

Amplicor

RT-PCR

Roche

50

NA

Diagnose active infection and assess

HCV Test v2.0*

Diagnostics

response to therapy

(Indiannapolis, IN)

Versant HCV

TMA

Bayer Corp,

5

NA

Diagnose active infection and assess

RNA Assay*

(Tarrytown, NY)

response to therapy

Ampliscreen

RT-PCR

Roche

<50

NA

Blood screening

HCV Test v2.0*

Diagnostics

(Indiannapolis, IN)

Procleix HIV-1/

TMA

GenProbe, San

<50

NA

Blood screening

HCV Assay*

(Diego, CA)

Quantitative

Amplicor

RT-PCR

Roche Diagnostics

600

2.9 log10

Determine duration of therapy and

HCV Monitor

(Indiannapolis, IN)

early prediction of therapy

Test v2.0

failure

Versant HCV

bDNA

Bayer Corp

615

4.1 log10

Determine duration of therapy and

RNA Assay v3.0*

(Tarrytown, NY)

early prediction of therapy failure

TaqMan HCV

Real-time

Roche Diagnostics

10

6.0log10

Diagnose active infection, assess

Analyte Specific

RT-PCR

(Indiannapolis, IN)

response to therapy, determine

Reagent

Abbott Molecular

duration of therapy, and

(Des Plaines, IL)

early prediction of therapy failure

*FDA-cleared tests.

NA, not applicable.

compare the performance characteristics with specimens submitted for HCV diagnosis.70 The difference in analytical sensitivity between the two tests does not result in any meaningful difference in clinical sensitivity when the tests are used diagnostically, because it is rare for patients with chronic hepatitis C infection to present for initial evaluation with viral loads of less than 105 copies/ml.

The Procleix HIV-1/HCV test (GenProbe, San Diego, CA) also uses TMA technology and is approved by the FDA for the screening of blood products.71 The Ampliscreen HCV RNA test v2.0 is an RT-PCR assay (Roche) designed for blood screening that is based on the Amplicor HCV test. Both assays have analytical sensitivities of less than 50IU/ml.

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