Evaluation of red blood cell size distribution histograms: the fraction of microcytes

A method is described for the assessment of the fraction of microcytes from the red blood cell (RBC) size distribution histogram. For quantification of the fraction of microcytes an upper threshold corresponding with a RBC volume of 70 fL is established. The reference interval for the fraction of microcytes covers a range from 0.01 to 0.09. In order to examine the relationship between the fraction of microcytes and the mean cell volume (MCV) values computer simulation studies were performed. The computer simulations are based on a Gaussian distributed reference RBC histogram as generated on a Technicon H 6000/H 601 Hematology Analyser. From our studies it is shown that determination of the fraction of microcytes yields a higher sensitivity than MCV values for detecting small populations of microcytes. In particular, measurement of the fraction of microcytes is very sensitive to minor changes in the MCV values if a normocytic RBC population combined with a microcytic RBC fraction shows a wide dispersion in their cell volumes.