Schilling test is done for?
Correct Answer: Vitamin B12 deficiency
Description: ANSWER: (A) Vitamin B12 deficiencyREF: Harrison's 18th ed ch: 105The Schilling test is performed to determine the cause for cobalamin malabsorptionSince cobalamin absorption requires multiple steps, including gastric, pancreatic, and ileal processes, the Schillingtest also can be used to assess the integrity of those other organs.Dietary cobalamin is bound in the stomach to a glycoprotein called R-binder protein, which is synthesized in both the stomach and the salivary glands. This cobalamin-R binder complex is formed in the acid milieu of the stomach.Cobalamin absorption has an absolute requirement for intrinsic factor, another glycoprotein synthesized and released by gastric parietal cells, to promote its uptake by specific cobalamin receptors on the brush border of ileal enterocytes.Pancreatic protease enzymes split the cobalamin-R binder complex to release cobalamin in the proximal small intestine, where cobalamin then is bound by intrinsic factor.Cobalamin absorption may be abnormal in the following:Pernicious anemia, a disease in which immunologically mediated atrophy of gastric parietal cells leads to an absence of both gastric acid and intrinsic factor secretion.Chronic pancreatitis as a result of deficiency of pancreatic proteases to split the cobalamin-R binder complexAchlorhydria, or absence of another factor secreted with acid that is responsible for splitting cobalamin away from the proteins in food to which it is boundBacterial overgrowth syndromes, which are most often secondary to stasis in the small intestine, leading to bacterial utilization of cobalamin (often referred to as stagnant bowel syndrome)Ileal dysfunctionProcedure:The Schilling test is performed by administering 58Co-labeled cobalamin orally and collecting urine for 24 h, and it is dependent on normal renal and bladder function.Urinary excretion of cobalamin will reflect cobalamin absorption provided that intrahepatic binding sites for cobalamin are fully occupied. To ensure saturation of hepatic cobalamin binding sites so that all absorbed radiolabeled cobalamin will be excreted in urine, 1 mg of cobalamin is administered intramuscularly 1 h after ingestion of the radiolabeled cobalamin.The Schilling test may be abnormal (usually defined as <10% excretion in 24 h) in pernicious anemia, chronic pancreatitis, blind loop syndrome, and ileal disease.Whenever an abnormal Schilling test is found, 58Co-labeled cobalamin should be administered on another occasion bound to intrinsic factor, with pancreatic enzymes, or after a 5-day course of antibiotics (often tetracycline).Differential Results of Schilling Test in Several Diseases Associated with Cobalamin (Cbl) Malabsorption 58Co-CblWith Intrinsic FactorWith Pancreatic EnzymesAfter 5 Days of AntibioticsPernicious anemia Chronic pancreatitis Bacterial over growth Ileal diseaseReducedReducedReducedReducedNormalReducedReducedReducedReducedNormalReducedReducedReducedReducedNormalReduced
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