Quantification of genotype 4 hepatitis C virus RNA by the COBAS AmpliPrep/COBAS TaqMan hepatitis C virus test

Clinical performance of the VERIS HCV assay for hepatitis C virus RNA quantification

BACKGROUND

Diagnosis of hepatitis C virus (HCV) infection and treatment monitoring rely on detection/quantification of HCV RNA and real-time polymerase chain reaction (PCR) techniques are expected to equivalently quantify the different HCV genotypes.

OBJECTIVE

The clinical performance of the VERIS HCV assay for HCV RNA quantification was compared to that of the Abbott RealTime HCV assay.

STUDY DESIGN

Qualitative concordance and quantitative comparison were evaluated on a first panel of 286 clinical samples containing HCV genotypes 1-6. Forty additional genotype 4 samples were tested to explore genotype 4 HCV RNA underquantification.

RESULTS

Qualitative discrepancies were observed for low viral loads (<2 log₁₀ IU/mL) in patients under antiviral therapy and would not have had any impact on patients' management with the current guidelines for the monitoring of patients on direct-acting antivirals (DAAs). Quantification results were well correlated (R²=0.89) with an overall minimal quantification bias (mean VERIS - Abbott difference) of -0.09 log₁₀ IU/mL. Quantification agreement for genotypes 1, 2 and 3 samples was excellent, but reached -0.57 log₁₀ IU/mL for 46 genotype 4 samples. A lower quantification bias of -0.24 log₁₀ IU/mL was observed when testing 40 additional genotype 4 samples with a second reagent lot. Underquantification was not associated with 5' untranslated region (UTR) sequence polymorphisms but could be explained by 5' UTR RNA molecular modeling.

CONCLUSION

HCV RNA quantification by the VERIS HCV assay and the Abbott RealTime HCV assay was well correlated for all HCV genotypes, except genotype 4 where 5' UTR RNA folding may impact quantification. Nevertheless, this underestimation of HCV RNA levels had no impact on clinical use.

Differences between quantification of genotype 3 hepatitis C virus RNA by Versions 1.0 and 2.0 of the COBAS AmpliPrep/COBAS TaqMan HCV Test

Background:

Differences between the designs of hepatitis C virus (HCV) viral load assays can result in genotype-related variability in RNA quantification. We tested paired aliquots of plasma specimens from HCV-infected individuals using two versions (v1.0 and v2.0) of the Roche COBAS AmpliPrep/COBAS TaqMan HCV Test (CAP/CTM HCV) and noted variability between results for a subset of specimens; we then sought to determine whether discrepant results were more prevalent among specific HCV genotypes.

Methods:

Archived and prospectively-collected plasma samples from 114 unique patients were tested using CAP/CTM HCV v1.0 and v2.0. The HCV genotype result for each patient was determined by retrospectively reviewing laboratory records.

Results:

All (46/46) specimens with quantifiable viral loads from patients with genotype 1 or 2 infection had CAP/CTM HCV v1.0 and v2.0 results that were within 0.5 log

Conclusions:

In patients infected with HCV genotype 3, sequential CAP/CTM HCV viral load results should be compared with caution and interpreted in the context of the specific assay version used.

Comparison of the QIAGEN artus HCV QS-RGQ test with the Roche COBAS Ampliprep/COBAS TaqMan HCV test v2.0 for the quantification of HCV-RNA in plasma samples

BACKGROUND

Quantification of Hepatitis C Virus (HCV)-RNA is important for the clinical management of patients undergoing antiviral therapy.

OBJECTIVES

To compare the quantification of clinical plasma samples by the Roche COBAS AmpliPrep/COBAS TaqMan HCV test v2.0 and the artus HCV QS-RGQ test.

STUDY DESIGN

HCV-RNA viral load in 155 plasma samples from HCV-seropositive individuals was determined using the COBAS test and retrospectively with the artus. Furthermore, a dilution series of an Acrometrix standard was tested with both tests in replicates of five to assess differences in limit of detection and precision.

RESULTS

Two clinical samples showed inhibition using the artus test and were excluded from analysis. Of the clinical samples, 20 tested negative in both tests, 7 tested positive in the COBAS test and negative in the artus test, and 126 samples were quantified by both tests. The mean overall difference between tests (artus-COBAS) was 0.27 log IU/mL. The mean difference of quantification varied little across genotype 1a, 1b, 2b and 3a (range: +0.15 to +0.35 log IU/mL). Both tests were precise (%CV at 1000 IU/mL 1.1 and 1.8 for the COBAS and artus test, respectively).

CONCLUSIONS

The limit of detection appeared lower in the COBAS test than the artus test when analyzed from a limited number of replicates. Both tests were precise with the artus test quantifying higher than the COBAS test on average. It is therefore recommended to monitor individual patients with the same test throughout treatment.

The Cobas AmpliPrep/Cobas TaqMan HCV test, version 2.0, real-time PCR assay accurately quantifies hepatitis C virus genotype 4 RNA

Accurate hepatitis C virus (HCV) RNA quantification is mandatory for the management of chronic hepatitis C therapy. The first-generation Cobas AmpliPrep/Cobas TaqMan HCV test (CAP/CTM HCV) underestimated HCV RNA levels by >1-log10 international units/ml in a number of patients infected with HCV genotype 4 and occasionally failed to detect it. The aim of this study was to evaluate the ability of the Cobas AmpliPrep/Cobas TaqMan HCV test, version 2.0 (CAP/CTM HCV v2.0), to accurately quantify HCV RNA in a large series of patients infected with different subtypes of HCV genotype 4. Group A comprised 122 patients with chronic HCV genotype 4 infection, and group B comprised 4 patients with HCV genotype 4 in whom HCV RNA was undetectable using the CAP/CTM HCV. Each specimen was tested with the third-generation branched DNA (bDNA) assay, CAP/CTM HCV, and CAP/CTM HCV v2.0. The HCV RNA level was lower in CAP/CTM HCV than in bDNA in 76.2% of cases, regardless of the HCV genotype 4 subtype. In contrast, the correlation between bDNA and CAP/CTM HCV v2.0 values was excellent. CAP/CTM HCV v2.0 accurately quantified HCV RNA levels in the presence of an A-to-T substitution at position 165 alone or combined with a G-to-A substitution at position 145 of the 5' untranslated region of HCV genome. In conclusion, CAP/CTM HCV v2.0 accurately quantifies HCV RNA in genotype 4 clinical specimens, regardless of the subtype, and can be confidently used in clinical trials and clinical practice with this genotype.

Second-generation Cobas AmpliPrep/Cobas TaqMan HCV quantitative test for viral load monitoring: a novel dual-probe assay design

Hepatitis C virus (HCV) RNA viral load (VL) monitoring is a well-established diagnostic tool for the management of chronic hepatitis C patients. HCV RNA VL results are used to make treatment decisions with the goal of therapy to achieve an undetectable VL result. Therefore, a sensitive assay with high specificity in detecting and accurately quantifying HCV RNA across genotypes is critical. Additionally, a lower sample volume requirement is desirable for the laboratory and the patient. This study evaluated the performance characteristics of a second-generation real-time PCR assay, the Cobas AmpliPrep/Cobas TaqMan HCV quantitative test, version 2.0 (CAP/CTM HCV test, v2.0), designed with a novel dual-probe approach and an optimized automated extraction and amplification procedure. The new assay demonstrated a limit of detection and lower limit of quantification of 15 IU/ml across all HCV genotypes and was linear from 15 to 100,000,000 IU/ml with high accuracy (<0.2-log(10) difference) and precision (standard deviation of 0.04 to 0.22 log(10)). A specificity of 100% was demonstrated with 600 HCV-seronegative specimens without cross-reactivity or interference. Correlation to the Cobas AmpliPrep/Cobas TaqMan HCV test (version 1) was good (n = 412 genotype 1 to 6 samples, R(2) = 0.88; R(2) = 0.94 without 105 genotype 4 samples). Paired plasma and serum samples showed similar performance (n = 25, R(2) = 0.99). The sample input volume was reduced from 1 to 0.65 ml in the second version. The CAP/CTM HCV test, v2.0, demonstrated excellent performance and sensitivity across all HCV genotypes with a smaller sample volume. The new HCV RNA VL assay has performance characteristics that make it suitable for use with currently available direct-acting antiviral agents.

The COBAS ® TaqMan ® hepatitis C virus assays: automated systems for accurate and sensitive viral load quantification

In recent years, the real time-based TaqMan(®) technology has allowed the development of highly sensitive hepatitis viral load tests with broad dynamic ranges. The increasing applications of these tests in clinical diagnostics have shown the utility of viral load as a predictive marker of treatment response and proven its key role in invidualized antiviral therapies. Future refinement in viral load assays, including higher sensitivity, genotype inclusivity, standardization and automation, will further foster the concept of personalized healthcare in the clinical management of chronic hepatitis C.

Development of a second version of the Cobas AmpliPrep/Cobas TaqMan hepatitis C virus quantitative test with improved genotype inclusivity

Hepatitis C virus (HCV) RNA measurement has been facilitated by the introduction of real-time PCR-based assays with low limits of detection and broad dynamic ranges for quantification. In the present study, the performance of two second-version prototypes of the Cobas AmpliPrep/Cobas TaqMan HCV Quantitative Test (CAP/CTM v2) with decreased sample input volume and improved genotype inclusivity was investigated. A total of 232 serum and plasma samples derived from patients with chronic hepatitis C (genotype 1 [GT1], n = 108; GT2, n = 8; GT3, n = 24; GT4, n = 87; GT5, n = 3; and GT6, n = 2) were processed in parallel with the Cobas AmpliPrep/Cobas TaqMan HCV Test (CAP/CTM), Cobas Amplicor HCV Monitor Test v2.0 (CAM), and two second-version prototype formulations of CAP/CTM, Mastermix 1 (MMx1) and MMx2. In addition, three GT4 transcripts containing rare variant sequences were tested. The mean log(10) HCV RNA differences for the best-performing CAP/CTM v2/MMx2 formulation in comparison to CAM were -0.05, 0.05, -0.12, -0.10, -0.44, and -0.29 for patients with GT1, GT2, GT3, GT4, GT5, and GT6 infections, respectively. GT1, GT2, and GT4 samples including isolates with known variants within the 5' untranslated region (G145A, A165T) that were underquantified with CAP/CTM were correctly quantified with the second-version prototype. In addition, CAP/CTM v2 was able to accurately quantify the three transcripts with rare variant sequences. In conclusion, CAP/CTM v2 accurately quantifies HCV RNA across all HCV genotypes, including specimens with rare polymorphisms previously associated with underquantification.