Vitamin B12 deficiency
Posted by dkwinter

See also: Vitamin deficiencies


Clinical features of VitB12 deficiency

  • Anemia (especially showing oval macromytes, hypersegmented neutrophils and circulating megaloblasts in the blood film)
  • History of autoimmune disease
  • History of glossititis or mouth ulcers
  • Parasthesiae, unsteadiness, or peripheral neuropathy
  • Malabsorption
  • History of metformin or prolonged PPI use
  • Neurocognitive impairment (in the elderly)


History to accompany Vit B12 lab requisitions

  • High risk of nutritional B12 deficiency
  • High risk of drug-related B12 deficiency
  • GI disease/surgery
  • Unexplained hematologic abnormalities
  • Unexplained neurologic abnormalities


Deficiency may be defined as a level less than 244 pg/L (180 pmol/L)

Replacement may be accomplished by daily PO doses of 1,000 mcg for 10 days then weekly for four weeks, then monthly for life.

On average, oral B12 is as effective as IM injection at achieving neurologic and hematologic response. Try it first.

B12 is available OTC as 100 mcg, 500 mcg, 1000 mcg, 5000 mcg tablets.