Evaluation of the Abbott RealTime HCV genotype II plus RUO (PLUS) assay with reference to core and NS5B sequencing

- The PLUS assay is an automated method that identifies HCV subtypes 1a, 1b and genotype 6 with 96%, 95% and 83% agreement respectively with gold-standard core/NS5B sequencing.
- The PLUS assay can aid in the resolution of certain HCV genotype samples with ambiguous results by the FDA-approved Abbott HCV GT II assay.
- The PLUS genotype 6 probe, designed to detect the genotype of subtypes 6c-6l, also correctly genotyped examples of 6a, 6m, 6n, 6o, 6q, 6r, 6s, and 6v in this study.
- The PLUS assay failed to identify 12/57 genotype 6 samples in this study, including some examples of 6a, 6b, 6e, 6m, 6l, 6q, and 6u.

BackgroundHCV genotyping remains a critical tool for guiding initiation of therapy and selecting the most appropriate treatment regimen. Current commercial genotyping assays may have difficulty identifying 1a, 1b and genotype 6.ObjectiveTo evaluate the concordance for identifying 1a, 1b, and genotype 6 between two methods: the PLUS assay and core/NS5B sequencing.Study designThis study included 236 plasma and serum samples previously genotyped by core/NS5B sequencing. Of these, 25 samples were also previously tested by the Abbott RealTime HCV GT II Research Use Only (RUO) assay and yielded ambiguous results. The remaining 211 samples were routine genotype 1 (n = 169) and genotype 6 (n = 42). Genotypes obtained from sequence data were determined using a laboratory-developed HCV sequence analysis tool and the NCBI non-redundant database.ResultsAgreement between the PLUS assay and core/NS5B sequencing for genotype 1 samples was 95.8% (162/169), with 96% (127/132) and 95% (35/37) agreement for 1a and 1b samples respectively. PLUS results agreed with core/NS5B sequencing for 83% (35/42) of unselected genotype 6 samples, with the remaining seven “not detected” by the PLUS assay. Among the 25 samples with ambiguous GT II results, 15 were concordant by PLUS and core/NS5B sequencing, nine were not detected by PLUS, and one sample had an internal control failure.ConclusionsThe PLUS assay is an automated method that identifies 1a, 1b and genotype 6 with good agreement with gold-standard core/NS5B sequencing and can aid in the resolution of certain genotype samples with ambiguous GT II results.