Vitamin B12 deficiency

Keywords: Pernicious anaemia


Appropriate Tests


Full blood count, Blood film, White cell count differential, Platelet count.

Vitamin B12 and Folate assays (RBC).

Bone marrow aspiration only occasionally required for diagnosis and/or confirmation.

Review clinical features for likely cause.

Methylmalonate, plasma, urine, homocysteine or holotranscobalamin have not been shown to be better predictors of response to treatment than the total serum vitamin B12 concentration. Their levels fluctuate with time and neither predict nor preclude cobalamin responsive haematological disorders*.



Lack of intrinsic factor

  • Pernicious anaemia

Intrinsic Factor Ab is specific but positive in only 60% of patients. Parietal cell antibodies have low specificity.

  • Post-gastrectomy

See also Blind loop syndrome, below.

Competition for dietary B12


  • Blind loop syndrome


Absence of ileal receptors for intrinsic factor/B12


  • Ileal resection


  • Crohn's disease


Dietary deficiency


  • Strict vegan


  • Breast fed infant of vegan



* Laurence Solomon: Blood 2005: 105(3), 978 - 985

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