Flow cytometry

Flow cytometry (FC) is a method for characterizing the counts and size distribution of particles, such as blood cells, in a fluid, . The original technique passed cells through pores in a membrane and measured the current produced; this was the Coulter Counter of 1953. Prior to this invention, blood cell counting was a laborious and variable manual procedure. In current laboratory medicine, it primarily is a laser-based fluorescence detection method used to characterize cell antigens on large numbers of hematopoetic or lymphoid cells in suspension typically derived from peripheral blood, bone marrow aspirate or lymph node tissue.

Laser-based flow cytometry instruments use a thin laminar flow of fluid to direct thousands of cells from a small diameter nozzle through a thin beam of laser light of a certain wavelength. The cells are categorized by size forward light scatter, cellular complexity or granularity side scatter. They may also measure the fluorescence of antigen-coupled dyes with which the cells have been treated, as with fluorescence intensity for each 'CD' clusters of differentiation marker. The antigen distribution for thousands of cells is printed in graphical histograms which a pathologist interprets individually and collectively to determine the phenotype of dominant cell populations in leukemias and lymphomas of various types.