Consensus recommendations for technical standardization of flow cytometric measurable residual disease assessment in B-cell acute lymphoblastic leukemia: A report from The Cytometry Society, India.

Measurable residual disease (MRD) assessment is a key determinant of risk stratification and treatment modification in B-cell acute lymphoblastic leukemia (B-ALL). Multicolour flow cytometry (MFC) is a globally adopted rapid and sensitive MRD technique. However, technical practices remain significantly variable across laboratories, compromising assay sensitivity, reproducibility, and comparability. Currently, systemic recommendations providing guidelines on the technical aspects of MFC-MRD in B-ALL are unavailable. The Cytometry Society (TCS)-India undertook a structured consensus process to standardize technical aspects of MFC-MRD testing. A two-round Delphi survey was conducted among laboratory professionals and clinicians across India to capture the prevailing practices and priorities. Consensus recommendations were prepared through survey findings and further refined during an in-person consensus congress with national and international experts from Australia, Egypt, Spain, and Russia. This document provides comprehensive recommendations across pre-analytic, analytic, and post-analytic phases of MFC-MRD including minimal antibody panel, best practices for sample collection, transport, and processing, Instrument setup, quality control, acquisition targets, gating strategies, approaches for LOD/LLOQ definition, hemodilution assessment, etc. A structured MRD report format with quality caveats is also provided. The recommendations are categorized into "Must," "Preferred," and "Acceptable" levels to suit diverse resource settings while promoting harmonization. Implementation of these standards will enhance assay sensitivity, reproducibility, and comparability, thereby strengthening MRD-guided clinical decision-making in B-ALL.