When performing bone marrow cell identification, it is necessary to differentiate the stages of erythrocyte development. This differs from a peripheral blood differential, where the term "nucleated red blood cells" ("NRBCs") is used to describe all stages of circulating normoblasts.
As with the myeloid sequence, there is a continuum in the erythroid maturation process in terms of nuclear and cytoplasmic morphology. Becoming familiar with the range of variation in each nucleated erythrocyte stage will make bone marrow differentials less intimidating.
The image to the right shows several different stages of erythroid maturation with several clusters of NRBCs all maturing together.