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Vitamin B12

Vitamins Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: Vitamins

Overview

Vitamin B12 (cobalamin) is a water-soluble vitamin essential for DNA synthesis, red blood cell formation, and nervous system myelination. A serum Vitamin B12 test measures the circulating total cobalamin and helps detect deficiency or excess. Low levels suggest risk for megaloblastic anemia, peripheral neuropathy, cognitive decline, or subacute combined degeneration of the spinal cord; high levels are less common and may reflect supplementation or underlying liver or hematologic disease. Testing is prompted by symptoms such as fatigue, pallor, paresthesias, gait disturbance, memory loss, or glossitis. Levels vary with age (older adults at higher risk of deficiency), dietary pattern (vegans/vegetarians), pregnancy (increased requirement), and certain medical conditions or medications.

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Test Preparation

No special preparation is required

Why Do I Need This Test

Profile: Included in the "Vitamins" panel.
Symptoms indicating test: persistent fatigue, unexplained anemia, numbness/tingling, balance problems, cognitive changes, or glossitis.
Conditions diagnosed/monitored: B12 deficiency, pernicious anemia, malabsorption, monitoring replacement therapy.
Reasons for abnormal levels: poor intake, malabsorption, pernicious anemia, medications, supplementation, liver/renal disease.
Biological meaning of abnormal values: low B12 → impaired DNA synthesis and demyelination; high B12 → usually excess intake or release from damaged tissue.
Behaviors/lifestyle causing abnormal values: strict vegan diet, chronic alcohol use, long-term PPI or metformin use.
Family history: autoimmune gastritis/pernicious anemia or inherited malabsorption disorders may prompt testing.

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Understanding Test Results

Values <200 pg/mL (<148 pmol/L) are generally consistent with deficiency and increase risk for megaloblastic anemia and neurologic injury; levels <100 pg/mL are associated with a high risk of severe neurologic damage.
Results 200–300 pg/mL (148–221 pmol/L) are borderline/possible deficiency; confirm with functional tests (methylmalonic acid or homocysteine) or clinical correlation.
Values 300–900 pg/mL (221–665 pmol/L) are usually adequate, but functional deficiency can rarely occur despite normal total B12.
Levels >900 pg/mL (>665 pmol/L) are commonly due to recent high-dose supplementation or release from liver disease, renal failure, or myeloproliferative disorders and warrant review of history and further evaluation if unexplained.

Normal Range

200-900 pg/mL OR 148-665 pmol/L

FAQs

Q: What are the sources of vitamin B12?

A: Vitamin B12 occurs primarily in animal-derived foods; people following plant-based diets obtain it from B12-fortified foods and reliable supplements. It’s also available as over-the-counter oral supplements and as prescription high‑dose tablets or intramuscular injections for deficiency. Health professionals recommend fortified foods or regular supplementation for strict vegetarians and older adults with absorption issues.

Q: What does the vitamin B12 do for your body?

A: Vitamin B12 helps make red blood cells and DNA, supports healthy nerve function and myelin formation, and is essential for normal brain and mood regulation. It aids energy metabolism by converting food into usable energy and helps control homocysteine levels, reducing cardiovascular risk. Deficiency can cause megaloblastic anemia, fatigue, numbness or tingling, balance problems and cognitive difficulties.

Q: What happens when vitamin B12 level is low?

A: Low vitamin B12 causes megaloblastic anemia (fatigue, pallor, shortness of breath), neurological symptoms (numbness, tingling, balance problems, memory loss, confusion), mood changes like depression, and a sore tongue. Long-standing deficiency can cause irreversible nerve damage and cognitive decline. It also raises homocysteine, increasing cardiovascular risk. Early detection and supplementation usually prevent progression.

Q: How can I raise my B12 levels fast?

A: To raise B12 quickly, get tested and follow medical advice. For significant deficiency, doctors often give intramuscular B12 injections (rapidly restores levels). If injections aren’t needed, high‑dose oral B12 supplements (e.g., 1,000–2,000 mcg daily) or sublingual forms plus B12-rich foods (meat, fish, dairy, fortified cereals) help. Recheck bloods and address underlying absorption causes. Consult your clinician before starting.

Q: Which fruits get B12?

A: Practically no fruits provide vitamin B12. B12 is naturally found in animal products (meat, fish, dairy, eggs) and in fortified foods and supplements. Some seaweeds and fermented plant products contain B12-like compounds, but their bioavailability is unreliable. If you follow a vegetarian or vegan diet, rely on fortified foods or a supplement after consulting a healthcare professional.

Q: What causes a B12 deficiency?

A: Vitamin B12 deficiency is caused by inadequate intake (strict vegan or poor diets), loss of intrinsic factor from autoimmune pernicious anemia, reduced stomach acid (atrophic gastritis or proton pump inhibitors), bariatric surgery or gastrectomy, intestinal disorders that impair absorption (celiac disease, Crohn’s), small intestinal bacterial overgrowth, certain parasites, and medications (long-term metformin). Risk increases with age.