The Schilling test is performed to evaluate vitamin B12 absorption. B12 helps in the formation of red blood cells, the maintenance of the central nervous system, and is important for metabolism. Normally, ingested vitamin B12 combines with intrinsic factor, which is produced by cells in the stomach. Intrinsic factor is necessary for vitamin B12 to be absorbed in the small intestine. Certain diseases, such as pernicious anemia, can result when absorption of vitamin B12 is inadequate.