Vitamin B12 Test is a microtiter plate test kit based on a microbiological assay which measures the total Vitamin B12 content in serum. Vitamin B12 (Cobalamin), a collective term for a group of various substituted corrinoide with cobalt as the central atom, is found free and also protein-bound in food. The protein-bound form is degraded by pancreatic protease, releasing free B12 which binds to intrinsic factor, a protein secreted by gastric parietal cells of the stomach mucosa. The Cobalamin-Intrinsic-Factor-Complex is bound to mucous membrane cells of the stomach in the ileum and absorbed by the cells. In the case of high doses, a diffusion of the complex also takes place. Vitamin B12 is bound to the protein Transcolbalamin II (TC-II) within the cells. TC-II serves as a transport protein for Vitamin B12 in the circulation system. Vitamin B12 is involved in the metabolism process as a co-enzyme, and plays an important role in the formation of the blood, the development of the nervous system and the regeneration of the mucous membranes. In addition, there is a direct relationship to the formation of folic acid because methylcobalamin is involved in the transfer of methyl groups for the synthesis of methionin from homocystein.Vitamin B12 deficiency is seldom caused by dietary factors. In most cases, it results from a resorption disorder of the intestines or defective development of intrinsic factor. Since vitamin B12 resorption could be reduced up to 50% in the elderly, an increased supplement is recommended. Pregnant women with a lacto-vegetarian diet are also recommended to increase the intake because their liver vitamin B12 stores may be exhausted.The classical vitamin B12 deficiency disease is pernicious anemia. In the early stages of the disease, vitamin B12 deficiency symptoms are manifested as weariness, palpitations, pallor or jaundice.The serum is pre-treated and diluted with a buffer mixture, and then samples were transferred in the wells of a microtiter platecoated with Lactobacillus delbrueckii subsp. lactis. The addition of vitamin B12 in either standards or samples gives a vitamin B12-dependent growth response until vitamin B12 is consumed. After incubation at 37°C for 44 - 48 hr, the growth of Lactobacillusplantarum is measured turbidimetrically at 610 - 630 nm (alternatively at 540 - 550 nm) in an ELISA-reader and a standard curve isgenerated from the dilution series. The amount of vitamin B12 is directly proportional to the turbidity.