Vitamin B12

Also written as: Cobalamin

A vitamin needed for nerve function and red blood cell production.

What it measures

The concentration of vitamin B12 circulating in blood.

Why a doctor orders it

Checked when anemia with large red cells is found, when nerve symptoms are described, and in people at higher risk of deficiency including those on long-term acid-reducing medication, after certain surgeries, and on plant-based diets.

What is generally associated with a higher result

Usually reflects supplementation. Elevated values without supplements are occasionally seen with liver and some blood conditions.

What is generally associated with a lower result

Broadly associated with dietary shortfall, absorption problems including pernicious anemia, long-term metformin or acid-reducing medication use, and some gastrointestinal surgeries.

Everyday things that move this number

Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:

Supplements, including multivitamins, which can normalize a genuinely low level
Pregnancy
Some medications

Questions to take to your appointment

If this is borderline, should methylmalonic acid be checked?
Could any of my medications be affecting absorption?

Build a printable questionnaire with your own results →

Where to read more

MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .

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