Iron and Anaemia

Abstract

The major part of the body’s iron is normally found in circulating red blood cells in the form of haemoglobin, essential for oxygen transport to the tissues. A reduction in the blood haemoglobin concentration, or packed red cell volume/haematocrit, to below that which is normal for a given individual (i.e. not limited by nutritional deficit or disease) is defined as anaemia. Threshold criteria for haemoglobin concentration (Table 7.1) and haematocrit have been defined; in adults lower limits for haemoglobin concentration of 130 g/l for males and 120 g/l for females are frequently used to define anaemia (Cook and Skikne, 1989). However, it should be recognized that these limits are not absolute and refer only to the likelihood (around 95%) of anaemia being present; in some individuals haemoglobin concentrations above the threshold are still lower than those normally maintained, while in others individual haemoglobin concentrations may normally be below the threshold. Any anaemia, whether due to iron deficiency or secondary to other conditions (see below), is necessarily associated with changes in the total amount, or the distribution, of body iron. Iron deficiency is the commonest cause of anaemia but in other forms of anaemia iron stores are usually increased (the iron previously in haemoglobin being diverted to macrophage stores). Indeed, in some ‘iron loading’ anaemias, notably the more severe thalassaemia disorders (see below), the need for regular blood transfusions and/or increased dietary iron absorption can lead to a marked excess of storage iron which is toxic, resulting in potentially fatal tissue damage.

Table 7.1 Haemoglobin concentrations below which amaemia is likely to be present at sea level.(source: WHO, 1972.)