Approach to an adult patient with a Macrocytic Anaemia

Compiled by Dr Rafiq Dhansay, Dr Trisha Moodley & Dr Jennifer Lines 3rd Quarter 2015

Macrocytosis is described as an increase in the volume or size of a red blood cell (RBC). The parameter on the
full blood count used to measure this, is the Mean Corpuscular Volume (MCV). An MCV >100 femtolitres (fL) is
considered macrocytic. On a peripheral blood smear, a red blood cell is considered macrocytic if it is larger than
the nucleus of a small mature lymphocyte. Macrocytosis may or may not be accompanied by anaemia.

The causes of a macrocytosis are broadly divided into five groups based on the mechanism:

  1. Abnormalities of DNA metabolism e.g. vitamin B12 and folate deficiencies and drugs that interfere with DNA
    metabolism.
  2. Increase in circulating immature red cells or “stressed” red cells, e.g. reticulocytosis in response to
    haemorrhage or haemolysis, aplastic anaemia, pure red cell aplasia, erythropoietin (EPO) effect.
  3. Primary bone marrow disorders, e.g. myelodysplastic syndromes, leukaemia.
  4. Lipid abnormalities, e.g. liver disease, hypothyroidism.
  5. Unknown mechanism.
The following table extract outlines conditions which may cause a macrocytic anaemia (CLICK HERE for the complete table).

Macrocytic_table_1

 

 

References:

  1. Schrier, SL. Approach to the adult patient with anaemia. In UpToDate. Mentzer, WC (Editor). (Accessed on
    January 22 2015).
  2. Schrier, SL. Macrocytosis. In UpToDate. Mentzer, WC (Editor). (Accessed on March 23 2015).
  3. Hoffbrand AV, Catovsky D, Tuddenham EGD, Green AR (Eds.). Postgraduate Haematology, 6th edition.
    Oxford, United Kingdom: Wiley-Blackwell; 2011.
  4. Bain BJ. Blood cells. A practical guide, 4th edition. Oxford, United Kingdom: Blackwell publishing; 2006.
  5. Tkachuk DC, Hirschmann JV (Eds.). Wintrobe’s atlas of clinical hematology, 1st edition. Philadelphia, USA:
    Lippincott Williams & Wilkins; 2007.