Vitamin B12 deficiency - Symptoms, Causes, Images, and Treatment Options

Diseases

Highlights & Basics

Key Highlights

Vitamin B12 (cobalamin) deficiency classically presents with megaloblastic anemia, but can also present with neurologic and neuropsychiatric complaints.
Older people, patients with chronic malabsorption, patients with a history of gastric resection or bypass, and those taking certain medications (metformin, proton-pump inhibitors) are at risk.
Early diagnosis is critical in preventing and halting the progression of neurologic disorders such as peripheral neuropathy, subacute combined degeneration of the spinal cord, and dementia.
Methylmalonic acid and homocysteine levels may help to diagnose vitamin B12 deficiency at an early, asymptomatic state.
Cause of vitamin B12 deficiency should be searched for once a diagnosis is confirmed.

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Definition

Epidemiology

Etiology

Pathophysiology

Images

Absorption of vitamin B12. Dietary B12 is released from food in the stomach and binds to R-protein (haptocorrin, this complex is stable in the gastric acidic environment). The R-B12 complex then travels to the duodenum, where B12 binds to intrinsic factor (IF, secreted by gastric parietal cells and therefore lost in pernicious anemia). This B12-IF complex is carried down the small intestine until the terminal ileum, where it attaches to IF receptors and is absorbed into the bloodstream bound to transcobalamin. Over 95% of dietary B12 is absorbed through the IF pathway

Citations

Key Articles

Devalia V, Hamilton MS, Molloy AM; British Committee for Standards in Haematology. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. Br J Haematol. 2014 Aug;166(4):496-513.[Abstract][Full Text]
Snow CF. Laboratory diagnosis of vitamin B12 and folate deficiency: a guide for the primary care physician. Arch Intern Med. 1999 Jun 28;159(12):1289-98.[Abstract][Full Text]
Stabler SP. Clinical practice. Vitamin B12 deficiency. N Engl J Med. 2013 Jan 10;368(2):149-60.[Abstract]
National Institutes of Health, Office of Dietary Supplements. Dietary supplement fact sheet: vitamin B12. 2022 [internet publication].[Full Text]
Guidelines and Protocols Advisory Committee, British Columbia. Cobalamin (vitamin B12) and folate deficiency. Jan 2023 [internet publication].[Full Text]

Other Online Resources

CDC: HIV - laboratory tests

Referenced Articles

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