Measurement of the mean cell volume using electronic particle counters.

Under carefully controlled conditions electronic cell counters, for example the Coulter Counter, Model FN, and Channelyzer, may be calibrated to give MCV values down to as small as 20 fl which agree with those derived from the centrifugation PCV (corrected for plasma trapping) and the red cell count. The MCV values will be too high if the instrument uses a high cell concentration, has a fixed lower threshold, no effective upper threshold and no edit facility. This may partly explain why the Coulter Counter, Model S, when standardized with 4C cell control gives higher MCV values than the Model FN linked to the Channelyzer. The difference is, on average, 2 fl with normal blood samples and 5 fl in cases of microcytic anaemia. It is suggested that standards of low MCV should be used together with those of normal MCV when calibrating the Model S.