Vitamin B12 deficiency

Vitamin B12 (cobalamin) deficiency classically presents with megaloblastic anemia, but can also present with neurologic and neuropsychiatric complaints.

Risk factors for vitamin B12 deficiency include older age (>65 years), gastric surgery (resection or bypass), chronic gastrointestinal illness (e.g., Crohn disease), vegan or strict vegetarian diet, and certain drugs (e.g., metformin, proton-pump inhibitors).

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.

Treatment with high-dose oral vitamin B12 therapy may be as effective as intramuscular vitamin B12 therapy.

Vitamin B12 is an essential vitamin; deficiency generally occurs with inadequate absorption or lack of dietary intake.

Vitamin B12 deficiency is a common condition that can manifest with neurologic, psychiatric, and hematologic disorders. While severe deficiency can cause permanent neurologic damage, earlier manifestations are generally subtle or asymptomatic.

The likelihood of vitamin B12 deficiency can be defined according to the serum vitamin B12 level as follows: <200 picograms/mL indicates probable deficiency; 200 to 350 picograms/mL indicates possible deficiency; and >350 picograms/mL indicates that deficiency is unlikely.[1]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. http://onlinelibrary.wiley.com/doi/10.1111/bjh.12959/full http://www.ncbi.nlm.nih.gov/pubmed/24942828?tool=bestpractice.com [2]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. http://archinte.ama-assn.org/cgi/content/full/159/12/1289 http://www.ncbi.nlm.nih.gov/pubmed/10386505?tool=bestpractice.com

Vitamin B12 level >350 picograms/mL does not exclude vitamin B12 deficiency, particularly if pernicious anemia is suspected. Spuriously normal or high serum vitamin B12 levels have been reported in patients with pernicious anemia due to anti-intrinsic factor antibody (anti-IFAB) interference in laboratory assays.[3]Tavares J, Baptista B, Gonçalves B, et al. Pernicious anaemia with normal vitamin B12. Eur J Case Rep Intern Med. 2019;6(2):001045. https://www.ejcrim.com/index.php/EJCRIM/article/view/1045 http://www.ncbi.nlm.nih.gov/pubmed/30931271?tool=bestpractice.com [4]Shah DR, Daver N, Borthakur G, et al. Pernicious anemia with spuriously normal vitamin B12 level might be misdiagnosed as myelodysplastic syndrome. Clin Lymphoma Myeloma Leuk. 2014 Aug;14(4):e141-3. http://www.ncbi.nlm.nih.gov/pubmed/24630920?tool=bestpractice.com [5]Yang DT, Cook RJ. Spurious elevations of vitamin B12 with pernicious anemia. N Engl J Med. 2012 May 3;366(18):1742-3. https://www.nejm.org/doi/full/10.1056/NEJMc1201655 http://www.ncbi.nlm.nih.gov/pubmed/22551146?tool=bestpractice.com [6]Mazokopakis EE. Normal serum cobalamin levels do not exclude the diagnosis of pernicious anaemia: a case report. Fam Pract. 2020 Feb 19;37(1):1-3. https://academic.oup.com/fampra/article/37/1/1/5709531 http://www.ncbi.nlm.nih.gov/pubmed/31953947?tool=bestpractice.com