Anaemia is very common, affecting over one- third of the world’s population and can be defined as a reduction in the haemoglobin content of red blood cells (RBC). The normal range varies slightly according to the population being tested, but typically in the UK anaemia in males can be diagnosed if the haemoglobin falls to below 135 g/ L and in females below 115 g/ L. In addition to a reduction in the haemoglobin concentration there is usually an as­sociated reduction in the number of circulating red cells and a low haematocrit. Anaemia is not a diagnosis, it is an abnormality that has an underlying cause and, therefore, a determination of that cause must be made before effective treatment can begin. The production of red cells is termed ‘haematopoiesis’ and occurs in the bone marrow (liver and spleen in foetal life). The bones involved in production change as we age from almost all bones in neonates to long bones, pelvis, and thoracic cage when we reach our 4th decade. As with all blood cells, production of RBCs begins with a pluripotent stem cell that is capable of forming many progenitor cells, including those of the erythroid (red cell) lineage (Figure 12.1). It is estimated that a single pluripotent stem cell, fol­lowing 18– 20 successful divisions, is able to produce 10 million mature erythrocytes. For this process to occur a number of growth factors (GF) are required, which act in synergy and enable the process of haematopoiesis to follow a stepwise maturation process, ending in the release of mature erythrocytes into the blood stream. Examples of such factors include the interleukins (IL), i.e. IL- 1, IL- 3, IL- 4, IL- 5, and IL- 6. Growth factors also act on the bone marrow stromal cells, enabling the correct environment for cell maturation and development. Tumour necrosis factor (TNF) and IL- 1 are particularly important stromal acting growth factors and can stimulate the stromal cells to produce many of the IL factors described above. The GF erythropoietin (EPO) is required for successful red cell maturation. Many of the growth factors work by binding to cell sur­face receptors.