Macrocytosis (possible causes of an macrocytosis (MCV >100fl) )

In almost all of these cases the condition causes macrocytosis by inhibiting cell division of the red cell precursors in the bone marrow

• less cell division gives rise to larger red cells
  
  

Causes include:

• Alcohol and/or liver disease (esp. if macrocytosis accompanied by thrombocytopenia but no or only mild anaemia)
  
  
• Vitamin B12/folate deficiency
  
  
• Pregnancy and newborn
  
  
• Hypothyroidism
  
  
• Haemolytic anaemia (where macrocytosis results from the presence of increased numbers of reticulocytes, which are larger than mature red cells, in the blood)
  
  
• Myelodysplasia
  
  
• Drugs esp anti-metabolites that interfere with DNA synthesis and cell division e.g.
  • Hydroxycarbamide
  • Azathioprine
  • Methotrexate
  • Trimethoprim
  • Zidovudine (AZT) and other nucleoside reverse transcriptase inhibitor treatments for HIV
    
    
• Aplastic anaemia or other causes of 'bone marrow stress'
  
  
• Acquired sideroblastic anaemia (very rare)

Reference:

• 1) Royal United Hospital Bath NHS Trust. Guidelines for the Investigation & Management of vitamin B12 deficiency (Accessed February 9th 2014)