Spurious elevation of the electronically determined mean corpuscular volume and hematocrit caused by hyperglycemia

Following normalization of blood glucose levels, a marked change in the MCV and in the calculated hematocrit was observed in five patients with transient severe hyperglycemia. The addition of varied concentrations of glucose to blood samples from healthy volunteers and from patients with microcytic, macrocytic, and normocytic anemia produced a similar and proportionate increase in the MCV. Increases in urea concentration to clinically relevant levels had no effect. The phenomenon appears to result from the osmotic swelling and subsequent shrinking of hyperglycemia erythrocytes when they are mixed with the diluent used for measurement of hematologic parameters. The magnitude of this spurious macrocytosis is less pronounced with the Coulter S than with the Coulter S-Plus. This difference can be explained by the differences in incubation prior to measurement of these instruments. A method for eliminating this spurious finding in blood samples with high levels of glucose is recommended.