Vitamin B12 is part of the B complex of vitamins and measurea the levels of vitamin B12 in the liquid portion of the blood, the serum or plasma, to detect deficiencies. Cobalamine, or vitamin B12, is found in animal products such as red meat, fish, poultry, milk, yogurt, and eggs and is not produced in the human body. In recent years, fortified cereals, breads, and other grain products have also become important dietary sources of B12. Vitamin B12 is necessary for normal RBC formation, tissue and cellular repair, and DNA synthesis. B12 is important for nerve health. A deficiency in B12 can lead to macrocytic anemia. Megaloblastic anemia, a type of macrocytic anemia, is characterized by the production of fewer but larger RBCs called macrocytes, in addition to some cellular changes in the bone marrow. B12 deficiency can lead to varying degrees of neuropathy, nerve damage that can cause tingling and numbness in the affected person's hands and feet.