Errors in automated reticulocyte counts due to Heinz bodies.

Serial reticulocyte counts on a patient with an unstable haemoglobin haemolytic anaemia whose red cells contained Heinz bodies were obtained by two automated methods. One false low and several false high counts were obtained with standard threshold settings; each was accompanied by activation of the appropriate alarm. With the FACScan a bimodal red cell distribution was found, corresponding to the proportions of Heinz body positive and negative cells. This case illustrates the fact that Heinz bodies can interfere with automated reticulocyte counting methods, and to a degree that could be clinically important.