What is Macrocytosis (raised MCV)?

by

Dr Zaid Ismail

An elevated mean corpuscular volume (MCV) indicates macrocytosis, commonly defined as MCV >100 fL. It’s often picked up incidentally on routine blood tests. The clinical significance varies and should be assessed in context.

Common Causes of Raised MCV

  • Alcohol excess – even without liver derangement or anaemia
  • Vitamin B12 or folate deficiency – may present with anaemia or neuropsychiatric symptoms
  • Liver disease – consider LFTs
  • Hypothyroidism – check TSH
  • Myelodysplastic syndromes – more likely in older adults with cytopenias
  • Medications – e.g. hydroxyurea, zidovudine, methotrexate, phenytoin
  • Reticulocytosis – e.g. post-bleed or haemolysis; reticulocytes are larger

Initial Investigations In Primary Care

  • Full blood count with blood film
  • B12, folate, TFTs, LFTs
  • Alcohol history
  • Medication review
  • Reticulocyte count (if haemolysis or recovery post-bleed suspected)

When to Refer

  • Unexplained macrocytosis with abnormal blood film or cytopenias
  • Suspected haematological malignancy
  • Persistently raised MCV despite correction of reversible causes

Red Flags

  • Neurological symptoms (B12 deficiency)
  • Weight loss, night sweats (possible haematological malignancy)
  • Macrocytic anaemia with low WBC or platelets

Guidance References

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