What is Flow Cytometry
Flow cytometry is a laboratory technique that rapidly analyzes individual cells or particles as they flow in single file through a laser beam, measuring their physical characteristics (size, granularity) and fluorescent properties to identify and quantify specific cell populations. 1, 2
Core Technical Principles
Flow cytometry operates through three integrated systems that enable multiparametric single-cell analysis 2, 3:
Fluidic system: Suspends cells in fluid and positions them to pass one-by-one through the laser beam at velocities of meters per second, enabling analysis rates approaching 100,000 cells per second 4
Optical system: Uses laser beams to illuminate cells, with detectors measuring light scattering (which characterizes cell size and granularity) and fluorescence emission from fluorochrome-labeled antibodies bound to specific cellular markers 1, 5
Electronics system: Converts optical signals into digital data for analysis, categorizing individual cells according to size, granularity, fluorochrome type, and fluorochrome intensity 1, 3
Immunophenotyping Process
The technique identifies specific cell populations through immunophenotyping, which relies on fluorochrome-labeled monoclonal antibodies that bind to antigenic determinants on cell surfaces 1:
Antibodies tagged with fluorescent dyes (such as phycoerythrin or fluorescein isothiocyanate) attach to specific surface or intracellular molecules 1, 5
As labeled cells pass through the laser beam, they emit fluorescent signals that identify which markers are present 2
Multiple fluorochromes with different emission spectra allow simultaneous detection of multiple markers on the same cell, enabling complex multiparametric analysis 5, 3
Key Advantages
Flow cytometry provides several unique capabilities that distinguish it from other diagnostic techniques 2, 5:
Speed: Analyzes thousands to millions of cells within minutes, providing statistically robust data on both rare and common cell populations 4, 5
Multiparametric analysis: Simultaneously measures multiple characteristics of individual cells, providing more specific information than single-marker techniques like immunohistochemistry 6, 2
Quantitative precision: Enables accurate cell counting through volumetric sample delivery and provides relatively quantitative assessment of cell populations 2, 4
Cell sorting capability: Can physically separate cell subpopulations based on measured parameters for further analysis or functional studies 2, 4
Primary Clinical Applications
Flow cytometry serves as the gold standard for numerous critical applications in clinical medicine 6, 4:
Hematological malignancies: Essential for diagnosis and monitoring of acute leukemias, chronic lymphoproliferative disorders, and plasma cell disorders including multiple myeloma 6, 7
Immunological monitoring: Used for CD4+ T-lymphocyte enumeration in HIV-infected persons, with measurements recommended every 3-6 months 1
Minimal residual disease detection: Enables quantitative evaluation of treatment efficacy and prediction of outcomes in hematological malignancies 6
Transplantation medicine: Detects alloantibodies in recipient sera with greater sensitivity than complement-dependent cytotoxicity assays 7
Technical Considerations
Proper implementation requires attention to standardization and quality control 1:
Universal precautions must be used with all specimens, with specific safety practices for handling potentially infectious materials 1
Sample quality significantly impacts results, with first-pull bone marrow aspirate samples recommended for optimal plasma cell enumeration 7
Discrepancies between flow cytometry and morphological assessment primarily relate to sample quality rather than technical limitations of the method itself 7