Vitamin B12 Deficiency

Hospitalize patients with pancytopenia, marked symptomatic anemia, or severe neurologic manifestations including subacute combined spinal degeneration, ataxia, dementia, or cognitive impairment, and begin urgent intensive cyanocobalamin or hydroxocobalamin therapy. Neurologic injury may be irreversible despite adequate replacement, making treatment urgency greater when gait dysfunction, weakness, sensory loss, or cognitive decline is progressive. BMJ+1BMJVitamin B12 deficiency - Management Approach | BMJ Best PracticeScienceDirectVitamin B12, folic acid, and the nervous system

Before the first dose when feasible, obtain CBC with hematocrit, reticulocyte count, serum B12, folate, and iron studies; collect confirmatory metabolite testing before replacement if the diagnosis is uncertain. Do not defer treatment in a patient with rapidly progressive neurologic or hematologic disease merely to complete testing. PubMed+1PubMedVitamin B12 (Cobalamin) - StatPearls - NCBI Bookshelfnice org ukRecommendations | Vitamin B12 deficiency in over 16s: diagnosis and management | Guidance | NICE

A megaloblastic anemia phenotype supports the diagnosis, but neurologic complications can occur without severe anemia. The inverse association between hemoglobin concentration and neurologic severity means a relatively preserved hemoglobin level does not provide reassurance in a patient with posterior-column symptoms, peripheral neuropathy, cognitive decline, or myelopathy. ScienceDirectScienceDirectVitamin B12, folic acid, and the nervous system

Start with serum B12 in patients with macrocytosis, anemia, neurologic symptoms, neuropsychiatric symptoms, or relevant nutritional and gastrointestinal risk factors. A low-normal B12 concentration can still reflect deficiency; an elevated serum methylmalonic acid supports functional cobalamin deficiency and is particularly useful when the initial B12 value does not match the clinical phenotype. ScienceDirect+2ScienceDirectVitamin B12 Deficiency - an overviewnice org ukGuideline Vitamin B12 deficiency in over 16sScienceDirectThe Many Faces of Cobalamin (Vitamin B12) Deficiency

Measure homocysteine as an adjunctive metabolic marker when available, but interpret it with methylmalonic acid rather than treating it as B12-specific: both homocysteine and methylmalonic acid are elevated in B12 deficiency. BMJ+1BMJAB0628 Vitamin B12, Homocysteine and Methylmalonic ...ScienceDirectThe Many Faces of Cobalamin (Vitamin B12) Deficiency Check folate concurrently because folate and B12 deficiency produce morphologically indistinguishable megaloblastic anemia, while neurologic injury is a key discriminator favoring B12 deficiency. PubMed+1PubMedVitamin B12 (Cobalamin) - StatPearls - NCBI BookshelfScienceDirectVitamin B12, folic acid, and the nervous system

If initial testing makes deficiency unlikely but symptoms or signs persist, repeat the original B12 test or obtain methylmalonic acid after 3 to 6 months. This interval applies to unresolved clinical suspicion rather than to progressive neurologic or hematologic illness, which warrants immediate reassessment and treatment. nice org uk+1nice org ukGuideline Vitamin B12 deficiency in over 16snice org ukRecommendations | Vitamin B12 deficiency in over 16s: diagnosis and management | Guidance | NICE

Classify the deficiency as dietary insufficiency, food-bound cobalamin malabsorption, autoimmune gastritis with intrinsic-factor failure, or terminal-ileal disease/resection. Clinically important deficiency is more likely to progress when intrinsic-factor-dependent absorption fails than when dietary intake alone is inadequate; most persistent causes evolve over years. ScienceDirect+1ScienceDirectVitamin B12 deficiency – A 21st century perspectiveScienceDirectHow I treat cobalamin (vitamin B12) deficiency

Order anti-intrinsic-factor antibody testing in B12 deficiency when autoimmune gastritis is suspected. Autoimmune injury to oxyntic gastric parietal cells reduces intrinsic factor and produces B12 malabsorption; autoimmune gastritis is the disease process historically associated with pernicious anemia. ScienceDirect+2ScienceDirectHave You Considered Pernicious Anemia?nice org ukGuideline Vitamin B12 deficiency in over 16snice org ukRecommendations | Vitamin B12 deficiency in over 16s: diagnosis and management | Guidance | NICE

Elicit prior terminal ileal resection, terminal ileitis, Crohn disease, and small-intestinal bacterial overgrowth. Patients with terminal ileal disease or resection are prone to B12 deficiency, and B12 replacement may be oral or parenteral depending on disease severity, absorption reliability, and response. ScienceDirect+1ScienceDirectVitamin B12 Deficiency - an overviewPubMedVitamin B12 (Cobalamin) - StatPearls - NCBI Bookshelf Deficiency may appear years after bariatric surgery because body stores delay clinical expression. ScienceDirectScienceDirectVitamin B12 Deficiency - an overview

Review diet and medication exposure. Strict vegan or vegetarian diets increase risk and justify maintenance-level replacement when deficiency risk is high. Long-term proton-pump inhibitor or histamine-2 receptor antagonist use is associated with lower B12 levels and should trigger review of ongoing indication, especially in older adults. BMJ+2BMJVitamin B12 deficiency - Management Approach | BMJ Best PracticeNatureProton-pump inhibitor use is associated with a broad spectrum of neurological adverse events including impaired hearing, vision, and memory | Scientific ReportsScienceDirectThe Many Faces of Cobalamin (Vitamin B12) Deficiency

Use intramuscular replacement initially for severe cobalamin deficiency, especially when neurologic disease, marked anemia, pancytopenia, or malabsorption is present. Cyanocobalamin is commonly used in the United States; hydroxocobalamin is used more commonly in Europe and is particularly useful in malabsorptive states. BMJ+2BMJVitamin B12 deficiency - Management Approach | BMJ Best PracticePubMedVitamin B12 (Cobalamin) - StatPearls - NCBI BookshelfPubMedHydroxocobalamin - StatPearls - NCBI Bookshelf

For hydroxocobalamin treatment of B12-deficiency anemia, a cited regimen is 1 mg intramuscularly every other day for 5 to 10 doses, followed by 1 mg every 3 months for maintenance. Intensive regimens over approximately 1 month are recommended for severe hematologic or neurologic disease, followed by ongoing maintenance treatment. BMJ+1BMJVitamin B12 deficiency - Management Approach | BMJ Best PracticePubMedHydroxocobalamin - StatPearls - NCBI Bookshelf

High-dose oral cyanocobalamin, including 1,000 mcg daily, can replenish B12 through passive absorption and has evidence of effectiveness comparable to intramuscular treatment in many patients, including those with Crohn disease and pernicious anemia. Select oral therapy only when the patient is clinically stable and can reliably adhere; choose parenteral therapy when oral adherence is doubtful or an irreversible malabsorptive cause is accompanied by severe disease. NEJM+4NEJMVitamin B12 DeficiencyBMJVitamin B12 deficiency - Management Approach | BMJ Best PracticePubMedVitamin B12 (Cobalamin) - StatPearls - NCBI BookshelfCochraneOral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency - Vidal‐Alaball, J - 2005 | Cochrane LibraryScienceDirectOral vitamin B12 supplementation in pernicious anemia

Avoid assuming that intranasal or sublingual preparations are interchangeable with established oral or intramuscular regimens; evidence and optimal dosing for those routes remain limited. BMJBMJVitamin B12 deficiency - Management Approach | BMJ Best Practice Cyanocobalamin is contraindicated in Leber hereditary optic neuropathy and is reported as contraindicated in renal insufficiency; confirm product-specific contraindications and select formulation accordingly. BMJBMJVitamin B12

At follow-up, assess the presenting phenotype directly: CBC and reticulocyte response for anemia or cytopenias; gait, proprioceptive symptoms, strength, paresthesias, and cognition for neurologic disease; and adherence to oral therapy or injection access. Follow-up is central because prevention of relapse depends on identifying the cause and maintaining effective replacement. PubMed+1PubMedVitamin B12 (Cobalamin) - StatPearls - NCBI BookshelfScienceDirectHow I treat cobalamin (vitamin B12) deficiency

For oral therapy in pernicious anemia, serial total plasma B12, homocysteine, and plasma methylmalonic acid have been used to assess biochemical response over one year. Persistent metabolite elevation, recurrent symptoms, or failure of hematologic recovery should prompt review of adherence, dosing route, ongoing malabsorption, coexisting folate or iron deficiency, and alternative diagnoses. PubMed+2PubMedVitamin B12 (Cobalamin) - StatPearls - NCBI BookshelfScienceDirectOral vitamin B12 supplementation in pernicious anemiaScienceDirectHow I treat cobalamin (vitamin B12) deficiency

Do not stop replacement solely because anemia corrects. Neurologic disease may coexist with minimal hematologic abnormality, and irreversible causes such as autoimmune gastritis, intrinsic-factor failure, and ileal resection require ongoing therapy to prevent recurrence. NEJM+2NEJMVitamin B12 DeficiencyScienceDirectVitamin B12, folic acid, and the nervous systemScienceDirectHow I treat cobalamin (vitamin B12) deficiency