Vitamin B-12 is an essential nutrient that plays a crucial role in the proper functioning of the nervous system, the production of red blood cells, and the synthesis of DNA. A Vitamin B-12 test is a diagnostic tool used to measure the levels of this nutrient in the blood. The test is often ordered by healthcare providers to investigate symptoms such as fatigue, weakness, or numbness and tingling in the hands and feet. The test can also be used to monitor the effectiveness of Vitamin B-12 supplementation in people with deficiencies or to evaluate the status of individuals with certain medical conditions, such as pernicious anemia or gastrointestinal disorders. A Vitamin B-12 test typically involves a simple blood draw, and results are usually available within a few days.