Vitamin B 12 is a precursor of DNA synthesis and lack of vitamin B 12 will impair DNA synthesis within a cell, however, RNA and protein synthesis are unaffected. These findings are most prominent in cells with rapid turnovers such as blood and GI tract. That is why B 12 deficiency can lead to hematologic changes such as megaloblastic anemia or megaloblastic changes in the GI tract. If these megaloblastic changes occur in the terminal ileum, vitamin B 12 absorption is inhibited. B 12 binds to R protein in the stomach.
R protein is found in gastric, biliary and salivary secretions.
Indications for the Schilling Test Low serum B 12 level with or without hematologic or neurologic symptoms. Confirm the diagnosis of vitamin B 12 malabsorbtion and determine the mechanism. Hematologic changes with non-diagnostic serum tests. This includes a macrocytic anemia which may involve a decrease in platelet and WBC count as well. To determine if a patient on long term vitamin B 12 therapy actually has an absorption defect.