Relationship of reticulocyte age to polychromasia, shift cells, and shift reticulocytes

Polychromatophilic erythrocytes on Wright-stained blood smears represent young reticulocytes. Ratios of polychromatophilic cells to total reticulocyte counts have been used to estimate marrow response to erythropoietin stimulation. These ratios, however, require both accurate counts of polychromatophilic cells on Wright-stained blood smears and reticulocytes on supravitally stained blood smears. Data from this study indicated that reticulocytes of Heilmeyer groups I, II, and III best represent polychromatophilic cells. Group III reticulocytes, however, were found in normal circulation and were difficult to distinguish from group IV reticulocytes. Groups I and II were not found in normal circulation and were easily identified on routine reticulocyte preparations. The term "shift reticulocyte" is proposed for reticulocytes of groups I and II only. The present study suggests that the "shift reticulocyte count," expressed as percent of 100 reticulocytes, is a more useful indicator of marrow response to anemia than total reticulocyte counts.