Mature red blood cells are anuclear, as they extrude their nuclei in the bone marrow prior to entering circulation. The presence of nucleated red blood cells is an abnormal finding.

The presence of nucleated red blood cells and left shift is referred to as a leukoerythroblastic blood film. If a patient has nucleated red cells on their film, always look for the presence of band forms, metamyelocytes and myelocytes.