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Blood Film

Red Blood Cells
White Blood Cells

Red Blood Cell Size



  • Small cells with mean corpuscular volume (MCV) <80 fL.
    • Causes of Microcytosis
    • Iron deficiency anaemia - nutritional deficiency, blood loss, malabsorption, pregnancy
    • Anaemia of chronic disease (chronic infection / inflammation / malignancy)
    • Thalassaemia
    • Congenital sideroblastic anaemia
    • Lead poisoning
    • Hyperthyroidism
    • Practical Points
    • Microcytosis is often associated with anaemia, but not always.
    • In thalassaemia, the MCV tends to be inappropriately low compared to the degree of anaemia.


  • Large cells with mean corpuscular volume (MCV) >100 fL.
    • Causes of Macrocytosis
    • Megaloblastic
    • B12 deficiency
    • Folate deficiency
    • Drugs - methotrexate, chemotherapy, reverse transcriptase inhibitors, valproate, phenytoin, nitrous oxide, trimethoprim
    • Non-Megaloblastic
    • Chronic liver disease
    • Chronic alcohol abuse
    • Post splenectomy
    • Aplastic anaemia
    • Myelodysplastic syndrome
    • Hypothyroidism
    • Reticulocytosis (haemolysis, haemorrhage, recovery post anaemia)
    • Practical Points
    • Macrocytosis without anaemia is often normal.
    • The classical findings on blood film for megaloblastic anaemia are macroovalocytes and hypersegmented neutrophils.
    • Macrocytosis with polychromasia is suggestive of reticulocytosis, and haemorrhage / haemolysis should be considered.