In iron deficiency, red cells do not develop the normal complement of iron–containing haemoglobin and the cells that form in the bone marrow are small (microcytic, low MCV) and hypochromic (low MCH and MCHC). The process of red cell maturation becomes prolonged so young red cells no longer contain large amounts of RNA and therefore do not appear polychromatic. As a result the anaemia is non- regenerative, with inappropropriately low reticulocyte counts. There is often a marked increase in variation in red cell shape (poikilocytosis) and red cell fragments (schistocytes) are often seen, as above. In cats, the red cells are often so small that platelets appear larger than red cells and this overlap in sizing can contribute to apparently very high platelet counts as some automated counters include some small red cells in the platelet count. Iron deficiency anaemia reflects chronic external blood loss, either through the gut associated with bleeding tumours or ulcers or occasionally with severe flea burdens and parasitic blood loss.