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NUTRIENTS & INFLAMMATION
Also printed as: B12 · Cobalamin · Vitamin B-12
Educational only — not medical advice.
B12 is a vitamin your body needs to build red blood cells, maintain nerve insulation, and produce DNA. You get it from animal foods and supplements, and absorbing it requires a specific process in the stomach and small intestine. The blood level reflects both intake and that absorption process.
B12 sits at the junction of the CBC and the nervous system — it can affect red cell size and nerve symptoms independently. Because the standard test has known blind spots, borderline values often warrant a second look.
TYPICAL ADULT RANGE
Many labs report roughly 200–900 pg/mL for adults, though clinicians often consider values below about 300 pg/mL borderline. Ranges vary by lab. Reported in pg/mL.
Reference ranges vary by lab, by method, and by age and sex. Always read your own result against the range printed on your report.
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Low B12 has common and identifiable causes: a plant-based or low-animal-food diet, reduced stomach acid with age, long-term use of acid-reducing medication or metformin, and conditions affecting absorption in the gut. It sometimes shows up first as a rising MCV or as tingling in the hands and feet. Because the serum test can look normal while tissue levels are low, doctors sometimes add methylmalonic acid or homocysteine for a clearer answer. What to take and how much is a decision for your clinician.
A high B12 is very often just supplementation — B12 is water-soluble and supplement doses far exceed dietary intake, so anyone taking a B-complex, an energy shot, or a multivitamin will read high. That is generally not a concern in itself. Less commonly, high levels appear with liver conditions or certain blood disorders, which is why a high B12 in someone taking no supplements at all is worth mentioning to your doctor.
Your doctor is the one who can read this number against your history, symptoms, and medications.
Educational only — not medical advice. Lab results only mean something alongside your history, symptoms, medications, and the rest of your panel. Bring questions to your doctor; they are the one who can interpret your results for you.
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