Stages of erythroid maturation showing red blood cell precursors

The first cell identifiable as an RBC precursor is the proerythroblast. It has a large oval nucleus with homogenous chromatin and distinct nucleoli and darkly basophilic cytoplasm. Subsequent cell divisions and synchronized maturation of the nucleus and cytoplasm lead to coarsening and clumping of the chromatin and shift of the cytoplasmic color as red-staining hemoglobin becomes more abundant and blue-staining RNA becomes less abundant. The orthochromatic normoblast is the last stage before the nucleus is extruded, leaving a reticulocyte (not shown). Refer to UpToDate topics on anemia and erythropoiesis for further discussions of the significance of these cells, their abnormalities, and their evaluation in patients with anemia.