VITAMIN B12

LAB67

7 mL Red Top Tube

2.0 mL

Protect from light

Refrigerate

Hemolysis 

Set Up:Daily Report Available:1 day

180-900 pg/mL

Vitamin B12 is a coenzyme for two physiologically important functions in humans, the synthesis of methionine, and the second is in the conversion of methylmalonic acid to succinic acid. Further reactions using these chemicals have an important role in the metabolism of fatty acids and aliphatic amino acids. In humans, the daily requirement for Vitamin B12 is approximately 0.5 mcg. The only significant sources of dietary Vitamin B12 of meats, milk or milk products, and eggs. In the stomach, vitamin B12 forms a complex with intrinsic factor (IF). When this complex reaches the distal ileum, it is bound by receptors on the surface of the mucosal epithelial cells and then enters the cells. Within those cells, the B12-IF complex dissociates, and the vitamin passes into the plasma. Most of the B12 is taken up by hepatocytes as the portal vein blood passes through the liver. It is stored within the liver and released into the plasma to meet physiological demands. If the quantity of vitamin B12 exceeds the capacity of the hepatocyte receptors, the kidneys excrete most of the excess. Since about 1 mg of B12 is stored in the liver, a quantity equivalent to the daily requirement for 2000 days, a dietary deficiency or impaired absorption does not become apparent for 5 years or more. Pernicious anemia, the most important disorder of vitamin B12 metabolism, is due to decreased secretion of IF. Antibodies to IF can be demonstrated in a large number of patients, suggesting that this disease is an autoimmune disease. This disease causes serious and often irreversible neurological disorders, such as burning pain or loss of sensation in the extremities, weakness, confusion, disorientation and dementia. Vitamin B12 deficiency occurs only rarely as a result of dietary lack of this vitamin. Common causes of high vitamin B12 levels include liver disease, myeloproliferative disease (with chronic myelogenous leukemia as a special case) and the use of multivitamin supplements.