Evaluation of Xpert^® BCR-ABL Ultra Using Different External Quality Assessment Reference Materials

Monitoring BCR-ABL transcript levels in patients on TKI therapy using real-time quantitative PCR is standard of care in the management of CML. In order to accurately assess treatment response, it is essential to ensure that variability in testing methodologies is tightly controlled. Xpert^® BCR-ABL Ultra, with sensitivity reaching MR4.5, is standardized in each production lot by using a secondary standard control panel derived from and aligned to the WHO International Scale (IS).

Here we describe the evaluation of Xpert^® BCR-ABL Ultra on various External Quality Assessment (EQA) reference materials, including USA/CAP, French/GBMHM and UKNEQAS LI BCR-ABL1, to further demonstrate the assay sensitivity, accuracy, reproducibility and precision.

For the 2016 CAP MRD-A BCR/ABL1 p210 survey, three panel members, MRD-01 (~20% IS), -02 (~0.002% IS), -03 (~0.2% IS), were tested and compared to the results obtained from the survey participants. MDR-01 was reported as 20% (IS), identical to the assigned baseline value. MRD-02 was reported as 0.0022% (IS), matching to the median value of 0.0020% (IS) and within the 2-fold range of 0.0010% to 0.0040% (IS) from 55% of 115 participants. MRD-03 was reported as 0.16% (IS), where the median value is 0.1847% (IS) with the 2-fold range of 0.09235% to 0.36940% (IS) from 67% of 167 participants.

For the French/GBMHM EQA evaluation, the goal was to develop a new panel preparation protocol using Xpert^® BCR-ABL Ultra sample prep reagents for assay reproducibility and precision assessment. After evaluated in a pilot study and the 1^st French/GBMHM EQA in France, the results showed that the new panel preparation protocol is suitable for EQA programs for quantification of BCR-ABL1 transcripts using Xpert^® BCR-ABL Ultra cartridges. A second French/GBMHM EQA round will be carried out to further validate the new panel preparation protocol for EQA.

For the UKNEQAS LI BCR-ABL1 panel evaluation, the goal was to develop a new sample prep protocol for processing lyophilised cell-line EQA samples to improve the Xpert^® BCR-ABL Ultra assay performance in the UKNEQAS LI BCR-ABL1 Quantification programme. The new sample prep protocol was developed and evaluated in the UKNEQAS LI BCR-ABL1 EQA Round, BCRQ 161702. The evaluation showed that the Xpert^® BCR-ABL Ultra inter-cartridge variation was improved with average %BCR-ABL/ABL (IS) reporting comparable to the consensus results obtained across all participants. The new sample prep protocol will be reviewed for further improvement before participating in the next round of UKNEQAS LI BCR-ABL1 Quantification programme, Trial 161703.