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Vitamin B12 in the blood
Medical expert of the article
Last reviewed: 05.07.2025
Reference values (norm) for the concentration of vitamin B 12 in blood serum: in newborns - 160-1300 pg/ml, in adults - 200-835 pg/ml (average values 300-400 pg/ml).
Vitamin B 12 (cyanocobalamin) is necessary for normal maturation of red blood cells. It functions as a coenzyme in the synthesis of nucleic acids (DNA and RNA) and methionine from homocysteine. Methionine is necessary for the conversion of folic acid into folinic acid, which ensures the normoblastic type of hematopoiesis. In addition, vitamin B 12 ensures the synthesis of lipoproteins in myelin tissue and glutathione. Therefore, vitamin B 12 deficiency is accompanied by the development of megaloblastic anemia, neutropenia and neurological disorders (funicular myelosis). Immunodeficiency with vitamin B12 deficiency is associated with the formation of hypersegmented neutrophils, characterized by reduced activity of the oxygen-dependent bactericidal mechanism, which is necessary for the destruction of intracellular bacteria and viruses.
The B 12 vitamins include several cobalamins contained exclusively in animal products. Alimentary deficiency of vitamin B 12 is rare. Vitamin B 12 is absorbed in the distal ileum. It is possible only after the vitamin forms a complex with the intrinsic factor, a glycoprotein secreted in the stomach. The specific carrier protein transcobalamin II transports cobalamins in the blood plasma. The absorption of the vitamin normally depends on the following factors: secretion of the intrinsic factor in the stomach; integrity of the mucous membrane of the distal ileum; the presence of transcobalamin II in plasma in sufficient quantities. Vitamin B 12 is necessary for the growth of certain intestinal bacteria, which prevent the absorption of this vitamin by competing for it with intestinal cells. Therefore, the absorption of vitamin B 12 can also be affected by the intestinal microflora.