Vitamin B12, also called cobalamin, is a vitamin absorbed in the last part of the small intestine with the help of a stomach protein, and it is required for the maturation of red blood cells and for the upkeep of nerve fibres. The blood level reflects the combined result of dietary intake, stomach and intestinal absorption, and the body's sizeable liver stores. It is measured mainly when anaemia with large red cells, or unexplained numbness and tingling, needs to be worked up.
No readings for this marker yet.
Low values most often follow a diet without animal foods, or impaired absorption — atrophic gastritis, autoimmune loss of intrinsic factor, coeliac or Crohn disease, surgery on the stomach or ileum, and long use of acid-suppressing drugs or metformin. Raised values are rarely a deficiency question and most often reflect supplements or injections; without them, high levels can accompany liver disease or blood disorders. Because stores empty slowly, symptoms may appear well before the level falls, and a result near the lower edge may be inconclusive. One out-of-range value is a reason to repeat the test and discuss it with a doctor.
Recent supplementation, an injection, or a B-complex taken shortly before the draw raises the measured level for days to weeks and can mask poor absorption; pregnancy and oral contraceptives tend to lower it. Borderline results are clarified by homocysteine and by methylmalonic acid, both of which rise when cellular B12 is genuinely short. Folate is read alongside it because the two deficiencies produce the same large-cell anaemia and folate alone can correct the blood picture while nerve damage continues.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.