Measurable Residual Disease.

Measurable residual disease (MRD) serves as a critical biomarker of prognosis, treatment efficacy, and clinical outcome. It captures the presence of residual tumor cells below the detection threshold of conventional microscopy. Multiparametric flow cytometry (MFC) offers a rapid, cost-efficient, and widely applicable platform for MRD detection through leukemia-associated immunophenotypes (LAIPs) and deviation-from-normal (DfN) antigen maturation patterns. This technique underpins a wide range of clinical applications, including risk stratification, therapeutic decision-making, and post-transplant surveillance.   This chapter outlines essential technical parameters for achieving high-sensitivity MRD detection across hematologic malignancies such as B-ALL, T-ALL, AML, MM, and CLL. Key topics covered include material required, reagent preparation, antibody panel design, sample processing and acquisition, gating strategies, and illustrative examples. Special emphasis is given to adaptations necessary for MRD monitoring following CD19-targeted therapies in B-ALL. By integrating rigorous methodology with evolving innovations, MFC continues to advance as a precise and expedient tool for MRD assessment, contributing significantly to personalized treatment strategies.