Vitamin B12 Test

About this test

This test measures the level of vitamin B12 (cobalamin) in your blood. B12 is an essential vitamin your body cannot produce on its own — it must come from animal products in your diet or from supplements. B12 is required for healthy red blood cell formation, proper nerve function, and DNA synthesis.

Deficiency develops slowly over months to years and can be well advanced before obvious symptoms appear. Left untreated, severe B12 deficiency causes irreversible neurological damage. It's most common in people who eat little or no animal products, those with certain digestive conditions, older adults with reduced stomach acid, and people on long-term metformin (diabetes medication).

Components

• Vitamin B12 (serum cobalamin): Measures the amount of B12 circulating in your blood. Low levels (typically below 200–300 pg/mL) indicate deficiency and may explain symptoms such as fatigue, weakness, tingling or numbness in the hands and feet, difficulty with balance, memory problems, and megaloblastic anemia (large, poorly functioning red blood cells). Because blood B12 can appear borderline-normal even when tissue deficiency is present, your clinician may also check methylmalonic acid (MMA) or homocysteine for a more complete assessment.

Who is this test for?

Vitamin B12 testing is recommended for vegetarians and vegans (B12 is found almost exclusively in animal products), adults over 50 (absorption declines with age), people taking metformin for diabetes (which reduces B12 absorption), and those with digestive conditions affecting the stomach or small intestine. Symptoms of B12 deficiency — including fatigue, tingling in the hands or feet, balance problems, and memory issues — can develop slowly and are often mistaken for other conditions.