ABSTRACT
The erythrocyte indices are red cell-based mean values that are mathematically derived from the erythrocyte count, hematocrit, and hemoglobin concentration of a blood sample. Their formulas were invented by Wintrobe (1933), and the indices have persisted as elements of hematology since that time. The implications of the indices, however, have been modied since their origin. Wintrobe’s hemograms were based on visual counting of erythrocytes in Neubauer counting chambers, and hematocrits were determined by centrifugation. Since then, the electronic counting of the erythrocytes has markedly increased the accuracy of the counts. And centrifugation of blood for the determination of the hematocrit is now recognized to yield imperfectly higher values because of the plasma trapped among the packed cells. Electronic methods of establishing the hematocrit obviate this inaccuracy because the volume of individual red cells is directly measured by the instrument and the hematocrit is mathematically computed from the erythrocyte count and the size of the red cells. It is noted, nevertheless, that under many circumstances, particularly in comparative hematology, the centrifuged microhematocrit is still employed and yields useful clinical information. The spun hematocrit, however, has limitations and is not ideal for many investigative studies.
