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Histopathology / Cytopathology / Hematopathology

Flow Cytometry

The technology of flow cytometry and the discovery of a method to produce monoclonal antibodies have made possible the clinical use of flow cytometry for the identification of cell populations.

Light scatter is utilized to identify the cell population(s) of interest, while the measurement of fluorescence intensity provides specific information about individual cells.

Monoclonal antibodies "tagged" with a fluorescent dye are commonly used for the identification of cell surface antigens and fluorescent dyes that directly and specifically bind to certain components of the cell (i.e. DNA) are used for cell cycle analysis.

The flow cytometer is able to rapidly screen large numbers of cells far beyond the capacity of traditional pathological or cytological methods. The information obtained aids in the diagnosis, classification, and prognosis of a variety of diseases.

Common uses for flow cytometry in the routine clinical laboratory include immune status evaluation, especially quantitation of CD4 positive T-cells in HIV positive patients, immunophenotyping of hematopoietic neoplasms and DNA cell cycle analysis of solid tumors.

Immune Status Evaluation Subpopulations of lymphocytes are identified and quantitated by the flow cytometer by utilizing monoclonal antibodies to various cell surface antigens.

Patients with acquired or congenital immunodeficiency disease and patients on immunosuppressive drug therapy exhibit characteristic alterations in lymphocyte populations.
Immunophenotyping Different cell populations that compose the hematopoietic system express distinctly different cell surface antigens at various stages of maturation. By detecting and measuring these expressed antigens, flow cytometry can aid in the classification of the cell lineage of leukemia and lymphoma.

Although not intended to be an independent diagnostic modality, flow cytometry is often able to subclassify hematopoietic malignancies beyond the capabilities of traditional morphologic and cytochemical techniques.
DNA cell cycle analysis Nuclear DNA is another parameter measured by flow cytometry. This measurement determines whether an abnormal DNA content is present (aneuploidy) and calculates the percentage of a cell population in each phase of the classic cell cycle. The percentage of cells in the S-phase gives an indication of the proliferative activity of that cell population.

Both of these parameters have been shown to have prognostic significance in various hematopoietic and solid malignancies.

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