Overview
Macrocytic (‘macro’ – large, ‘cytic’ – cell) anaemia describes anaemia (low haemoglobin) and an increased mean cell volume (MCV). It is divided into two forms:
- Megaloblastic macrocytic anaemia
- Non-megaloblastic macrocytic anaemia
It may be helpful to look at the chapter on Anaemia: Data Interpretation alongside reading this section to help wrap your head around when to suspect what type of anaemia.
Megaloblastic Causes
Overview
Megaloblastic macrocytic anaemia is characterized by large, oval-shaped red blood cells and hypersegmented neutrophils (neutrophils with 6 or more lobes) may be present. This occurs due to impaired DNA synthesis. Red blood cells cannot replicate DNA quickly enough, therefore, they become too large before division.
Causes
Causes of megaloblastic anaemia include:
- Vitamin B12 deficiency
- Folate deficiency
- Methotrexate
- Sulfasalazine
Non-Megaloblastic Causes
Overview
Non-megaloblastic anaemia is characterized by large red blood cells in the absence of problems with DNA synthesis. There are no hypersegmented neutrophils.
Causes
Causes of non-megaloblastic anaemia include:
- Chronic, excess alcohol consumption
- Liver disease
- Hypothyroidism
- Pregnancy
- Reticulocytosis
- Myelodysplastic syndromes
- Hereditary spherocytosis
Investigations
Overview
- Full blood count (FBC):
- Haemoglobin: low
- Mean cell volume (MCV): raised
- Blood film:
- Megaloblastic anaemia: enlarged red blood cells, hypersegmented neutrophils
- Non-megaloblastic anaemia: enlarged red blood cells, no hypersegmented neutrophils
