Imprecision of ratio-derived differential leukocyte counts.

Differential leukocyte counts are very imprecise if determined as the product of a total WBC and a percentage obtained by differentiation of a relatively small number of cells. The imprecision can be decreased by increasing simultaneously the numbers of both the counted and the differentiated cells. An increase of only one (such as by automated counting of the WBC) without a simultaneous increase of the other one does not lead to an appreciable reduction of the imprecision.