Serum levels of hepatitis C virus RNA predict non‐response to interferon therapy: comparison of two commercial assays

Abstract

We compared two commercial assays for quantification of serum hepatitis C virus (HCV) RNA to investigate whether pretreatment levels of serum HCV RNA could predict the outcome of interferon (IFN) therapy. The Amplicor HCV Monitor test is based on a single, combined reverse transcription and amplification reaction carried out by the Tth DNA polymerase using specific primers for the 5' untranslated (UTR) region. The Quantiplex HCV RNA 2.0 assay is based on specific hybridization of viral RNA by synthetic oligonucleotides complementary to the 5'-UTR and core regions of the genome, allowing equal quantification of the six major genotypes. Receiver-operating characteristic (ROC) analysis was employed to identify the best cut-off value (predicting patients who were non-responsive to treatment) with corresponding sensitivity and specificity values. Logistic regression analysis was performed using these cut-off values. We studied 133 consecutive patients with chronic hepatitis C enrolled in a prospecsustained responders was 5322 copies ml-1 by the Monitor test and less than 0.2 million equivalents ml-1 (MEq ml-1) by the Quantiplex assay; for the 115 non-responders/relapsers, the median viraemia was 83,125 copies ml-1 and 1.128 MEq ml-1 for the Monitor test and Quantiplex assay, respectively. Spearman's rank test gave a correlation of 0.63 between assays. The best predicting cut-off values were 22,134 copies ml-1 for the Monitor test and 0.330 MEq ml-1 for the Quantiplex assay; their respective sensitivities and specificities were 72% and 75% for Monitor and 67% and 83% for Quantiplex. By logistic regression analysis, the age and gender-adjusted odds ratios of high vs low HCV RNA levels, defining the risk of non-response, were 10.6 (CI 3.1-35.7) for Monitor and 14.3 (CI 4.3-47.3) for Quantiplex. The two assays had comparable sensitivity for serum HCV RNA but they identified different predictive cut-offs for non-response to therapy.

Improved Version 2.0 Qualitative and Quantitative AMPLICOR Reverse Transcription-PCR Tests for Hepatitis C Virus RNA: Calibration to International Units, Enhanced Genotype Reactivity, and Performance Characteristics

“…Thus, the fact that the HCV MONITOR tests underestimate viral loads above 5.0 ϫ 10 5 IU/ml may not be a limitation. Indeed, several studies have shown that the first version of the AM-PLICOR HCV MONITOR test and the Quantiplex HCV test, which does quantitate viral loads above 10 6 copies/ml, are equally accurate for predicting response to therapy from baseline viral load (26,32). Future studies that use international units per milliliter as a standardized reporting format should identify a prognostic cut-off.…”

“…The AMPLICOR products have been used successfully for diagnosis (10,12), prognosis (11,26,31,32), and monitoring therapy (13,35). Furthermore, a proficiency study found that laboratories using the first version of the qualitative AMPLI-COR HCV and quantitative AMPLICOR HCV MONITOR tests obtained more-accurate results than laboratories using either in-house reverse transcription (RT)-PCR HCV tests or other commercially available HCV tests (16).…”

“…Additionally, assays that use the same unit of measurement give different results for the same sample; thus, copies measured by one assay format are not equivalent to copies measured by another assay format. Also, the viral load cut-off used to predict response to therapy is assay specific (11,26,31,32). These limitations can be overcome by adopting a commonly accepted standard of measurement, the international unit.…”

Performance Characteristics of a Quantitative, Homogeneous TaqMan RT-PCR Test for HCV RNA

“…Nucleic acid amplification tests for HCV RNA have contributed to our understanding of the natural history of hepatitis C virus (HCV) infection and to the clinical management of chronic hepatitis C. Quantitative viral load tests are used for prognosis, [1][2][3][4][5][6][7][8][9] for evaluating new treat-ment regimens, 10 and for modifying treatment 11 or deciding whether to administer follow-up treatment. 12 A recent analysis of data from two multicenter studies indicates that pretreatment viral load, together with genotype, sex, age, and extent of fibrosis, can be used to decide whether patients should be treated with interferon plus ribavirin for 24 or 48 weeks.…”