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अमूर्त

Flowcytometry: Principle, Interpretation of result and its role in solid tumors

Amar Ranjan Singh

Flowcytometer is equipment which has become an integral part for the diagnosis of hematolymphoid malignancies. The word ‘flow’ means to pass, ‘cyto’ means cell & ‘metry’ means measurement. The flowcytometry is the passage of cells in single file (line or row) in front of a laser to be detected, counted and sorted. Cells labeled with fluorochrome are striked by laser to emit light (fluorescence) at varying wavelengths. Fluorescence (photon) is filtered and collected to convert the result into a digitalized (numerical) value. The reading is done by specialized software. Cells of interest flow through a liquid stream. The speed of flow of cell is higher than the speed of fluid carrying the cell (sheath fluid). This results into arrangement of cells in a single line (single file). This mechanism is called Hydrodynamic focusing. Up to 50000 cells per second can be measured, but the normal throughput is 1000 – 10000 cells/ sec (1). Detectors of photons are called photomultiplier tube. The detector placed in the line of light beam measures Forward Scattering (FSC) [size] and that of placed perpendicular to the light stream measures Side Scattering (SSC) [granularity, nuclear structure]. For all practical purposes cells falling in the range of 3-20 µ in diameter can be analyzed (2). Identification of rare cells at frequencies as low as 0.0001% has been reported.