Differential diagnosis

A vitamin B12 deficiency megaloblastic anaemia must be distinguished from other causes of a megaloblastic anaemia, principally a folate deficiency. These two causes are usually readily distinguished by analysis of the blood levels of these two vitamins.

It is also necessary to distinguish pernicious anaemia from other causes of vitamin B12 deficiency. Possible other causes of vitamin B12 deficiency include:

• a vegan diet: this is a diet that is devoid of all meat or animal products, e.g. cow's milk, dairy cheese
• gastrointestinal disease: vitamin B12 deficiency may result from any disease involving the terminal ileum or a bacterial overgrowth in the small bowel
• pancreatic disease: chronic pancreatic disease; Zollinger-Ellison syndrome
• previous surgery: gastrectomy or ileal resection
• rare causes of vitamin B12 deficiency:
  • fish tapeworm
  • congenital deficiency of intrinsic factor or transcobalamin II
  • nitrous oxide: this inactivates intrinsic factor