Vitamin B12 deficiency

Last updated: Thursday, 23, December, 2010
CausesAppropriate Tests

FBC, blood film, differential WCC, 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 transcobalamin have not been shown to be better predictors of response to treatment than the total serum B12 concentration. Their levels fluctuate with time and neither predict nor preclude cobalamin responsive haematological disorders*.


Lack of intrinsic factor

  • Pernicious anaemia
Intrinsic factor antibodies are 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 forintrinsic factor/B12

  • Ileal resection

Dietary deficiency

  • Strict vegan
  • Breast fed infant of vegan

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