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• Iron deficiency is commonest cause of anaemia
• Body has limited ability to absorb iron
• Excess loss of iron through bleeding is common

Body iron distribution

• 65% of body iron is in haemoglobin
• 30% is in ferritin and haemosiderin
• 3% is in myoglobin
• Erythropoesis occurs in bone marrow
• Iron is transported to bone marrow by plasma transferrin
• Transferrin obtains iron mainly from reticulo-endothelial system (RES)
• Only small proportion comes from dietary iron
• Some iron is stored in RES as ferritin and haemosiderin

Ferritin

• Ferritin is a water-soluble protein-iron complex
• Made up of apoferritin and iron-phosphate-hydroxide core
• 20% of its weight is iron
• Synthesis is stimulated by the presence of iron
• Iron is in the ferric (3+) form

Haemosiderin

• Haemosiderin is an insoluble protein-iron complex
• 40% of its weight is iron
• Formed by lysosomal digestion of ferritin

Dietary iron

• Iron is present in food as ferric hydroxide and ferric-protein complexes
• Meat and liver is good source of dietary iron
• Average western diet contains 10-15mg of iron
• 5-10% is absorbed in duodenum and jejunum
• Absorption is increased in pregnancy and iron-deficiency states
• Daily iron requirements are 1-2 mg per day

Iron absorption

• Absorption is favoured by acid and reducing agents
• Better absorbed in ferrous (2+) form
• The amount of iron absorbed is controlled in the epithelial cells
• Excess iron forms ferritin and is shed with the cells into the gut lumen
• Iron enter the plasma in the ferric form

Iron transport

• Most iron is transported to the bone marrow
• Used in mainly for erythropoesis
• Binds to transferrin in the portal blood
• About 6g of haemoglobin are produced each day
• Requires about 20mg of iron
• Total plasma iron turns over about seven times per day

Transferrin

• Transferrin is a beta-globulin
• Synthesised in the liver
• Half-life of 8-10 days
• Each molecule binds two iron atoms
• Normally only about 30% saturated
• Erythroblasts have transferrin receptors

Iron deficiency

• Usually due to chronic blood loss
• Occurs from GI tract or associated with menorrhagia
• Rarely due to dietary deficiency or malabsorption
• Asymptomatic until RES stores of iron are depleted

Laboratory features

• MCV, MCH and MCHC are all reduced
• Cells appear hypochromic and microcytic
• Target cells and pencil-shaped poikilocytes are seen
• Reticulocyte count is low relative to the degree of anaemia
• Platelet count maybe raised
• Serum iron is low
• Total iron binding capacity is increased
• Serum ferritin is low
• If bone marrow examination is performed, iron is absent from macrophages

Author:  Dr Shakeeb Khan

Last updated: 05 January 2008

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