BCR-ABL1 (p210) Transcript Kinetics

Context.— Delta checks are a powerful technique for monitoring clinical assays in many disciplines but have not been routinely used in molecular testing. Objective.— To determine if the biologically determined kinetics of BCR-ABL1's rise and fall could allow the development of a delta check in BCR-ABL1 testing. Design.— Nine years of BCR-ABL1 p210 results were evaluated and patients with 3 or more results were selected for inclusion. The kinetics of these percentages of international standard values were plotted against time along with the median and the 90th and 95th percentile lines. A Monte Carlo simulation of a batch mix-up was performed for 6 months of data to determine the efficacy of the proposed cutoff. Results.— The median kinetics showed a 1-log drop of the percentage of international standard in 90 days, with less than 5% of cases showing faster than a 2-log drop in 90 days, and less than 2.5% showing a faster than 3-log drop in 90 days (extrapolated to 1 log in 30 days). The Monte Carlo simulation of a batch mix-up showed that an average batch mix-up of 23 samples could routinely be flagged by this cutoff, albeit with wide variance. Conclusions.— These results suggest that using a drop in the percentage of international standard of greater than 1 log in 30 days can be a useful trigger in implementing a delta-check system for this molecular test.