B-084 Comprehensive Individualized Quality Control Plan (IQCP) Implementation and Analytical Verification of BCR-ABL1 p210 Transcript Quantification on the GeneXpert Platform

Abstract

The BCR::ABL1 fusion is a critical diagnostic marker in Chronic Myeloid Leukemia (CML), and quantitative measurement of BCR::ABL1 transcripts by RT-PCR is essential for therapeutic monitoring. The Xpert® BCR-ABL Ultra (Cepheid) is an automated, cartridge-based system that integrates sample preparation and RT-PCR with fluorescent detection, targeting the predominant p210 transcript. In CLIA-certified laboratories, an Individualized Quality Control Plan (IQCP) is required when quality control (QC) materials are not tested daily with patient specimens. We developed and implemented an IQCP for the Xpert assay in 2022 and repeated the process following installation of a new instrument in 2026. This study presents a comparative analysis of IQCP performance between the two instruments, along with over 36 months of weekly QC monitoring data using commercially available external controls. The Xpert BCR-ABL1 IS panel (MMQCI, C130) that includes reference materials with BCR::ABL1 concentrations of 0%, 0.0032%, 0.01%, 0.1%, 1%, and 10% on the International Scale (IS) was used in this study. For IQCP development and analytical verification, the 0.01% (low positive control) and 1% (high positive control) panel members were tested on eight consecutive daily runs in our new instrument. Expected MR ranges were established using the mean molecular response (MR) value ±2 standard deviations (SD). For ongoing quality control, the 0% (negative), 0.01% (low positive), and 1% (high positive) controls were tested weekly with clinical testing for approximately thirty-six weeks. QC monitoring also included evaluation of significant shifts in control values associated with reagent cartridge lot changes or control material lot variations. Eight consecutive daily runs of the positive controls yielded mean minimal residual (MR) values of 4.12 ± 0.16 for the low positive control and 1.83 ± 0.12 for the high positive control. In comparison, the corresponding 2022 values were 4.09 ± 0.29 (low positive) and 1.87 ± 0.20 (high positive), demonstrating minimal variation between the two evaluations. Based on these data, the established mean ± 2 standard deviation (SD) acceptance ranges were 3.80-4.44 (2026) versus 3.51-4.68 (2022) for the low positive control, and 1.59-2.07 (2026) versus 1.48-2.26 (2022) for the high positive control. Ongoing weekly QC monitoring over 36 months of patient testing, encompassing 10 lots of the Xpert assay kit and 5 lots of the Xpert BCR-ABL1 IS panel, demonstrated minimal variability (low positive mean 4.10 ± 0.24; high positive mean 1.86 ± 0.13). Overall, four QC failures were observed; however, all results remained within ± 2 SD of the established means. Minor shifts in positive control values were noted following assay lot changes but did not exceed the predefined mean MR ± 2 SD acceptance criteria Our laboratory implemented an IQCP for the Xpert BCR-ABL assay with weekly QC monitoring. Longitudinal QC analysis demonstrates sustained assay performance, minimal variability, and no significant deviations over 36 months of patient testing. Analytical verification of the new GeneXpert instrument using the Xpert® BCR-ABL Ultra demonstrated performance comparable to the previous instrument, with faster turnaround time and reduced hands-on workflow.