English: Normal mature RBCs are devoid of a nucleus. However, immature, nucleated red cells or progenitor red cells do. Normally, nucleated RBCs are found only in foetal circulation and new-born infants. After infancy, RBCs normally only contain a nucleus during the very early stages of the cell's life, and the nucleus is ejected as a normal part of cellular differentiation before the cell is released into the bloodstream. The presence of erythroblast in an adult's peripheral blood is suggestive increased pressure on the bone marrow to produce red cells to compensate for the anaemia Common causes include haemolytic and other chronic anaemia, chronic hypoxemia, myelofibrosis, thalassemia, cancers involving bone marrow (myelomas, leukemias, lymphomas).