Sources of physiological variation in differential leukocyte counting.

A statistical analysis is provided on the diurnal and day-to-day variations of individuals in order to validate the usefulness of high precision differential counts. There is a significant within-day variability that interferes with monitoring of individual patients unless a constant time of day is chosen for sampling. An experiment with endotoxin illustrates possible changes that can be monitored with highly precise counts, and several examples are given of monitoring patients over the course of an illness. Conclusions are that all the cell types of the differential respond independently to a variety of physiological and pathological stimuli. Information obtained will be as valuable as the care with which sample acquisition and other factors are controlled.