EVALUATION OF A METHOD FOR COUNTING ABSOLUTE NUMBERS OF CELLS WITH A FLOW CYTOMETER

We evaluated a method for performing absolute cell counts of lymphocyt e populations with a flow cytometer, In this method, TruCount, test tu bes that contain a known number of brightly fluorescent polystyrene be ads are provided by the manufacturer, Whole anticoagulated blood is ac curately pipetted into the tubes and mixed with fluorochrome-labeled m onoclonal antibodies, the erythrocytes are lysed, and this mixture is analyzed on the Bow cytometer, Absolute counts of lymphocyte subsets a re calculated by determining the ratio of beads to the cell population of interest and then multiplying this ratio by the number of beads in the tube, We found this method to be reproducible. The values we obta ined by the TruCount method were 5 to 10% higher than those obtained b y conventional methods (flow cytometry and automated hematology) used to determine absolute numbers of cells, We believe that these differen ces are due to the methods of determining absolute cell counts and not to faulty identification of lymphocyte subsets.