Vitamin B12 Deficiency Vitamin B12 (also called Cobalamin) is necessary for the formation of normal RBCs. Intrinsic factor, secreted by parietal cells in the gastric mucosa, binds with vitamin B12. Intrinsic factor is required for absorption of vitamin B12, which takes place in the terminal ileum. SX - Various GI symptoms, including weight loss and poorly localized abdominal pain, may occur. Neurologic symptoms. PE - Full. DX - • CBC, MCV and vitamin B12 and folate levels. • Sometimes methylmalonic acid levels or Schilling test. Schilling test: The Schilling test is useful only if diagnosing intrinsic factor deficiency is important, as in classic pernicious anemia. The Schilling test measures absorption of free radiolabeled vitamin B12. Radiolabeled vitamin B12 is given orally. TX - • Supplemental vitamin B12. • Vitamin B12 1000 to 2000 μg po can be given once/day to patients who do not have severe deficiency or neurologic symptoms or signs. • For more severe deficiency, vitamin B12 1 mg IM is usually given 1 to 4 times/wk for several weeks until hematologic abnormalities are corrected; then it is given once per month.