Microcytic anaemias
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Anaemia is one of the most common presenting complaints to general practice. One of several ways in which anaemias can be classified, is by red cell size. As such, anaemias can be said to be:

  • Microcytic (small RBCs)
  • Normocytic (RBC size within the normal range)
  • Macrocytic (large RBCs) – see macrocytic anaemias

Differentiating the cause of microcytic anaemias is important because the treatments can be different. The most common cause of microcytic anaemia is iron deficiency anaemia – which itself can have many underlying causes – but it is also important to consider anaemia of chronic disease and the haemoglobinopathies – such as thalassaemia – especially in iron deficiency presenting in children.

Microcytic anaemia can be identified on blood film (looking at the red blood cells under the microscope) and noting the small size of the cells (more formally the low mean corpuscular volume or low MCV), as well as the hypochromia (reduced colouring – i.e. the cells appear more pale). See below the normal blood film (top) and microcytic anaemia of iron deficiency (bottom). Note that these images have different levels of magnification – and when measured the cells of microcytosis will always be smaller than those of a normal film.

Normal blood film
Normal blood film
Microcytosis seen on blood film in iron deficiency anaemia
Microcytosis seen on blood film in iron deficiency anaemia


  • Diet history – particularly if diet is low in iron
    • In children – also ask about cow’s milk intake (should be <500mls per day)
    • Cow’s milk itself doesn’t cause iron deficiency, but children who drink more than 500mls / day tend to eat less food and thus are at risk of iron deficiency
    • Also – intake of java bean / broad beans – can precipitate haemolysis in G6PD deficiency
  • Family history
  • History of blood loss
    • Menorrhagia in females
    • GI bleeding – ask about stool colour, haemorrhoids
      • Be aware that the bleeding is often occult – consider faecal occult blood test


  • Pallor
  • Pale conjunctive
  • Tachycardia
  • SOB – especially on exertion
  • Lethargy
  • Poor concentration
  • Weakness
  • Heart failure
  • Failure to thrive (in children)


  • FBC – Hb <90 g/L is particularly significant
    • Microcytosis (small RBCs)
  • Iron studies
    • If normal, but patient has microcytic anaemia, request Hb electrophoresis
    • Elevated HbA2 >3.5% (+/- elevated HbF) suggests beta thalassaemia
    • Alpha thalassaemia requires genetic testing for diagnosis
Investigation pathway for microcytic anaemia
Investigation pathway for microcytic anaemia. Note: it may not always be indicated to perform Alpha Thalassaemia genetic testing – this decision is made on the basis of FHx, and the history of the patient – e.g. if there is no FHx of thalassaemia, and there are reasons for anaemia of chronic disease, this differentiation may be made on clinical grounds.

Red flags

Consider urgent hospital admission for anybody with:

  • Hb <70g/L (local policies may vary with a cut-off of 60-80g/L for transfusion)
  • Tachycardia
  • Murmur
  • Signs of heart failure
    • Signs of haemolysis, dark urine, jaundice
  • Co-existing thrmobocytopaenia or neutropenia
    • May indicate malignancy

Microcytic anaemia in children

  • Occurs in 8% of all children in Australia
  • The most common cause of anaemia in children
  • The reference range for children is different from adults:
    • 2 months – 90 g/L
    • 2-6 months – 95 g/L
    • 6-24 months – 105 g/L
    • 2-11 years – 115 g/L
    • 12+ – 120g/L (female) and 130g/L (male)
  • Differentials in children
    • Iron deficiency
    • Thalassaemia
    • G6PD deficiency


  • Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
  • Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
  • Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy
  • Anaemia – RCH

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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