Bridging variability: toward standardized and harmonized multiplex bead-based flow cytometric cytokine assays

Cytokine profiling has become an important tool in clinical laboratories, providing key insights into patients' immune status and therapeutic responses. Among various analytical techniques, multiplex bead-based flow cytometry has emerged as a key platform for high-throughput cytokine quantification owing to its superior sensitivity, specificity, and multiplexing capability. Nevertheless, substantial intra- and inter-laboratory variability remains a major obstacle, compromising reproducibility and diagnostic accuracy, ultimately constraining broader clinical application. This review comprehensively summarizes the methodologies and key procedural aspects of multiplex bead-based flow cytometric cytokine assays, identifies the principal sources of variability, and highlights recent advances in assay standardization and harmonization. Furthermore, it proposes strategic frameworks that emphasize collaborative efforts among clinical laboratories, instrument manufacturers, and regulatory agencies. Collectively, these initiatives, by providing a practical framework for standardizing and harmonizing multiplex cytokine assays in bead-based flow cytometry, are expected to pave the way for uniform measurements across diverse clinical settings, thereby enhancing assay reliability and clinical applicability.