A number of conditions may be associated with impaired utilization of vitamin B12 (cobalamin), so called "cobalamin-resistance."
Criteria:
(1) clinical and laboratory findings of cobalamin deficiency (increased methylmalonic acid, homocysteine, etc)
(2) normal folate and vitamin B12 concentrations
(3) correction of condition by administering high doses of vitamin B12
Conditions associated with impaired utilization of vitamin B12 (cobalamin):
(1) hereditary inborn errors of cobalamin metabolism (rare)
(2) age >= 70 years of age
(3) renal insufficiency
(4) diabetes mellitus
