Flow Cytometry — Cellular analysis using laser technology

Flow cytometry is an analytical platform that measures the light scatter and fluorescence emitted by single cells as they flow in single file through an optical detection path. Cells from blood, bone marrow, or liquefied tissue are tagged with monoclonal antibodies linked to fluorescent dyes, targeting specific cell surface, cytoplasmic, or nuclear antigens called clusters of differentiation (CD markers).

As each labelled cell crosses the laser path, light scatters forward and sideways to measure cell size and internal complexity, while fluorescence detectors measure the intensity of specific antibody binding. The resulting multi-parametric data allows hematopathologists to identify, quantify, and characterise distinct immune and tumour cell subpopulations with extreme precision within minutes.

Flow cytometry is essential for correctly diagnosing blood cancers, identifying precisely which white blood cell lineage has turned malignant. It categorises conditions that appear identical under an ordinary microscope into distinct sub-types requiring different therapies. Furthermore, its extreme sensitivity makes it an indispensable tool for tracking measurable residual disease (MRD), detecting tiny quantities of lingering cancer cells after treatment to confirm true remission or forecast early disease relapse.

Flow cytometry is an analytical test performed on blood, bone marrow aspirates, cerebrospinal fluid, or fine needle aspirates. It evaluates extensive panels of diagnostic CD markers, such as CD3, CD4, and CD8 for T-cells; CD19, CD20, and CD22 for B-cells; and CD33, CD34, or CD117 for myeloid precursors, differentiating malignant clones from healthy cellular equivalents.

Flow cytometry is predominantly employed in haematological malignancies. It is standard practice in diagnosing and monitoring acute myeloid leukaemia (AML), acute lymphoblastic leukaemia (ALL), chronic lymphocytic leukaemia (CLL), multiple myeloma, myelodysplastic syndromes, and various forms of Hodgkin and non-Hodgkin lymphoma.

The immunophenotype identified by flow cytometry directly dictates targeted treatment selection. For instance, demonstrating robust CD20 expression in B-cell lymphoma indicates that therapy should include anti-CD20 monoclonal antibodies like rituximab. Identification of specific marker combinations directs patients towards targeted therapies, CAR-T cell infusions, or allogeneic stem cell transplantation, while post-treatment MRD monitoring tells clinicians whether to intensify or safely de-escalate therapy.