cobas CMV is a new, automated, high-throughput assay for use on the cobas 6800/8800 systems that quantifies CMV DNA in EDTA-plasma. It can be run in mixed batches with other assays due to a uniform assay design.

Reproducibility of cobas CMV was determined by testing plasma spiked with Merlin virus at 0-5×10⁶ IU/mL across multiple days, reagent lots, and operators at 3 laboratories. Concordance between cobas CMV and CAP/CTM CMV was evaluated using longitudinal samples from solid organ transplant (SOT; 1913 samples from 107 subjects) and hematopoietic stem cell transplant (HSCT; 1367 samples from 257 subjects) recipients who participated in clinical trials for CMV prophylaxis. Clinical concordance at representative viral load thresholds (e.g., 1,800 IU/mL) and for decision to stop antiviral therapy (2 sequential results <137 IU/mL) was determined. Method comparison analysis used an initial viremic sample from each SOT or HSCT subject plus an additional 68 clinical and 219 contrived samples.

cobas CMV was highly reproducible with an SD of <0.11 log IU/mL and an overall detectable difference of <0.31 log IU/mL for all panel members. The lowest concentration member had the most variability, due to within-run random error. Among SOT recipients, cobas CMV and CAP/CTM CMV were concordant at a 1,800 IU/mL threshold, with 96.7% overall agreement. The decision to stop therapy was >86.2% concordant, with cobas CMV usually resulting in a longer duration of therapy. Among HSCT recipients, both assays were concordant at a 1800 IU/mL threshold with 99.3% overall agreement. The decision to stop therapy was 100% concordant. For contrived samples made from cultured virus, the 2 test results agreed closely. When results for clinical samples were compared, cobas CMV yielded higher viral loads than CAP/CTM CMV with a bias of 0.25 log IU/mL and 0.16 log IU/mL in SOT and HSCT recipients, respectively.

The new cobas CMV is highly reproducible and is calibrated to the WHO standard. Possibly due to limitations in the commutability of the standard, cobas CMV may yield higher CMV DNA values than CAP/CTM CMV in clinical samples, but both assays generated concordant results necessary for clinical decision making. Note: cobas CMV is not available in all markets; performance characteristics are subject to FDA approval.

CITATION INFORMATION: Baum P, Yao J, Butcher A, Hemyari P, Valsamakis A, Young S. Reproducibility of the Cobas CMV Test (cobas CMV) and Clinical Concordance with the Cobas Ampliprep / Cobas TaqMan CMV Test (CAP/CTM CMV). Am J Transplant. 2017;17 (suppl 3).

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