Vitamin B12 (cobalamin) is an essential nutrient required for red blood cell formation, DNA synthesis, and proper nervous system function. This test measures the amount of B12 in the blood and is crucial for diagnosing B12 deficiency, which can cause megaloblastic anemia and serious neurological problems. B12 deficiency commonly occurs due to pernicious anemia (an autoimmune condition affecting B12 absorption), dietary insufficiency (especially in vegetarians), or malabsorption disorders. Symptoms of B12 deficiency include fatigue, weakness, numbness, tingling in hands and feet, memory problems, and balance issues. Early detection and treatment with B12 supplements can prevent permanent nerve damage and improve quality of life. This test is often ordered as part of anemia workups or when evaluating neurological symptoms.