Megaloblastic anaemia

Last updated: Monday, 20, December, 2010
CausesAppropriate Tests

FBC, blood film (often pancytopenia; oval macrocytes, hypersegmented neutrophils). Serum vitamin B12 and RBC folate assays.

Elevated bilirubin and LD are due to haemolysis, including intramedullary haemolysis.

Bone marrow aspiration rarely required to confirm diagnosis.

Review clinical findings to guide investigation of cause.

See also Anaemia

Vitamin B12 deficiency

Folate deficiency


See Folate deficiencyVitamin B12 deficiency for drugs interfering with absorption.

Inhibition of folate metabolism, especially

  • Methotrexate 

Predictable effect.

  • Trimethoprim 

In susceptible individuals.

Inactivation of vitamin B12

  • Nitrous oxide 

Prolonged exposure, especially anaesthetists.

Inhibition of pyrimidine, purine synthesis, DNA assembly, especially

Predictable effect.

  • Azathioprine
  • 6-Mercaptopurine
  • 5-Fluorouracil
  • Cytosine arabinoside
  • Cyclophosphamide
  • Zidovudine (AZT)

Inborn errors of metabolism 

Rare - consult pathologist.

  • Orotic aciduria