Flow cytometry: From cell counting to high-dimensional cytometry

Flow cytometry has evolved from early photoelectric cell-counting methods into a sophisticated, high-dimensional single-cell platform that is indispensable in biomedical research and clinical laboratories. Its historical development reflects the integration of diverse technological modalities, including hydrodynamic focusing, light scattering, fluorescence, monoclonal antibody technology, laser optics, digital electronics, and computational analysis. Conventional flow cytometry remains a cornerstone of immunophenotyping, the diagnosis of hematological malignancies, measurable residual disease assessment, transplantation immunology, selected infectious disease immune monitoring, and translational drug and vaccine development. Technological advances, including spectral flow cytometry, imaging flow cytometry, mass cytometry, microfluidic platforms, large-particle cytometry, and nanoparticle flow cytometry, have expanded its analytical scope beyond intact cells to include organoids, extracellular vesicles, and complex immune environments. The current challenge lies not only in acquiring multiparametric data but also in ensuring the reproducible design, validation, interpretation, reporting, and clinical integration of these datasets. Future developments are expected to prioritize full-spectrum acquisition, artificial intelligence-supported automated analysis, miniaturization for point-of-care use, standardized quality management, and the integration of multimodal approaches with genomic, proteomic, metabolomic, and imaging techniques. This review summarizes the past, present, and future of flow cytometry, highlighting its system architecture, analytical workflows, current platforms, clinical and research applications, quality requirements, limitations, and emerging role in precision diagnostics.

Keywords: Flow cytometry, immunophenotyping, single-cell analysis, spectral flow cytometry