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Megaloblastic anaemia due to bacterial overgrowth of the small intestine is due to vitamin B12 malabsorption. This report describes a patient with bacterial overgrowth of the small intestine who had megaloblastic anaemia and malabsorption of vitamin B12, but persistently normal levels of serum vitamin B12 and normal serum and red cell folate levels. However, there was evidence of vitamin B12 deficiency as shown by an abnormal deoxyuridine suppression test and by the response to treatment with physiological doses of vitamin B12. A relative increase in biologically inactive vitamin B12 analogues may be the explanation for the normal vitamin B12 level in this patient.

Original publication




Journal article


Br J Haematol

Publication Date





7 - 12


Aged, Anemia, Macrocytic, Anemia, Megaloblastic, Female, Humans, Intestine, Small, Vitamin B 12, Vitamin B 12 Deficiency