CRRM1.5: anaemias 101/11/07

Learning Outcomes

Describe the way iron is handled in the body; including daily requirements

  • In a typical diet, 10-30mg of iron is consumed daily; only around 10% is actually absorbed
  • The amount of iron in the whole body averages at around 2-3g, most of which is part of haemoglobin
  • Dietary iron, found primarily in meat and vegetables, is absorbed in the duodenum of the small intestine, typically as ferrous iron (Fe2+)
  • Some iron is stored as ferritin in the liver; most is transported to bone marrow sites under the action of iron transferin (ferric iron only; regulated by erythropoietin) to contribute to haemopoiesis
  • When RBCs break down to release bilirubin, this is broken down in the liver to make bile as well as the kidney, from which it is excreted in urine
  • Iron passes through duodenal cells through one of two pathways:
  • Ferrous iron is absorbed directly and is able to pass straight out of the cell and into the plasma via the baso-lateral transporter, after which it is typically oxidised to ferric iron for binding to transferin
  • Ferric iron is bound to mobilferrin which transports it across the cell after which it binds to transferin for transport into the plasma; this pathway has a highaffinity but lowcapacity
  • Some ferric iron is reduced in the gut and ferritin / mobilferrin are able to exchange between iron oxidation states within gut cells
  • Iron is generally retained in the body since it is only lost by blood loss and via the intestine / bladder
  • The total iron binding capacity (TIBC) is a measure of the number of ‘free’ transferin molecules in the plasma
  • Iron absorption favours acidic conditions; caffeine and phytic acid (found in beans and pulses) reduce absorption

Explain the roles of blood loss, dietary, growth causing anaemia

  • Anaemia is defined as a lower than expected amount of haemoglobin in the blood (normal amounts vary between age groups, sex etc.)
  • Common symptoms include excessive tiredness, breathlessness on exertion, dizziness, pallor, poor resistance to infection and a weak, rapid pulse
  • Complications of anaemia include glossitis (inflammation of the tongue), angular stomatitis (cracking at the corners of the mouth), koilonychia (‘spoon-shaped’ nails) and pica (craving for non-food items)
  • Anaemias are classified according to blood indices:
  • Low MCV (microcytic RBCs[TG1]) implies iron deficiency anaemia(reduced Hb production – also reduced serum iron, increased TIBC) or possibly thalassaemia (normal iron / ferritin levels)
  • High MCV (macrocytic RBCs) can imply either:
  • Vitamin B12or folate deficiency if there are abnormal precursors to RBCs found in bone marrow (megaloblastic)
  • A non-specific liver problem if RBC production is normal, e.g. from alcohol abuse (normoblastic)
  • Normal MCV implies acute blood loss
  • Iron deficiency anaemia – the most common anaemia in the world – canbe caused by many things and requires further investigation, for example:
  • Blood loss – usually from GI tract
  • Increased demand – e.g. in pregnancy, lactation, growth
  • Reduced absorption – e.g. from gastrectomy (reduced acid) or coeliac disease (reduced intestinal absorption)
  • Poor diet – generally contributes rather than causes specifically
  • Normal MCHC should be 12 – 18gdL-1:
  • 9 – 11 is classified as mild anaemia
  • 6 – 9 is classified as moderate anaemia (difficulty breathing)
  • 2 – 6 is classified as severe anaemia (risk of cardiac failure)
  • Total iron binding capacity (TIBC) is increased in iron deficiency anaemia; bodily ferritin levels are reduced
  • Oral iron supplements are usually sufficient as treatment; occasionally in severe cases parenteral[TG2] injections are administered, e.g. deep into muscles

[TG1]Microcyte: abnormally small RBC

[TG2]Administered by any way other than the mouth