Schilling test

Vitamin B12 is also used to perform the Schilling test, which is used to diagnose pernicious anemia. 

Schilling test, 727 Schrodinger, E., 16 Schrodinger equation, 17 scientific method, F2 scientific notation, AS scintillation counter, 711 sea of instability, 705 second, F6, A3 second derivative, A9 second ionization energy, 43 second law of... 

Further investigation by administering radiolabeled B12 (i.e., Schilling test) to determine if lack of intrinsic factor. 

Vitamin B12 (cyanocobalmin) administered both orally and parenterally is equally effective in treating anemia from vitamin B12 deficiency. However, use of parenteral cyanacobalamin is the most common method of vitamin B12 replacement because it may be more reliable and practical. Subcutaneous or intramuscular administration is appropriate. Vitamin B12 is absorbed completely following parenteral administration, whereas oral vitamin B12 is absorbed poorly via the GI tract. Furthermore, use of parenteral vitamin B12 to treat megaloblastic anemia may circumvent the need to perform a Schilling test to diagnose lack of intrinsic factor. 

Vitamin B-12 absorption test Vitamin B-12 absorption test (Schilling test). 

Management is essentially the same as for folate deficiency but the site of the lesion, that may necessitate further investigation and treatment, needs accurate definition by means of the Schilling test. Additional useful determinations are homocysteine and methylmalonic acid levels. 

Nickoloff E. Schilling test physiologic basis for and use as a diagnostic test. Crit Rev Clin Lab Sci 1988 26 263-76. 

Once a diagnosis of megaloblastic anemia is made, it must be determined whether vitamin B12 or folic acid deficiency is the cause. (Other causes of megaloblastic anemia are very rare.) This can usually be accomplished by measuring serum levels of the vitamins. The Schilling test, which measures absorption and urinary excretion of radioactively labeled vitamin B12, can be used to further define the mechanism of vitamin Bi2 malabsorption when this is found to be the cause of the megaloblastic anemia. 

Pernicious anemia results from defective secretion of intrinsic factor by the gastric mucosal cells. Patients with pernicious anemia have gastric atrophy and fail to secrete intrinsic factor (as well as hydrochloric acid). The Schilling test shows diminished absorption of radioactively labeled vitamin B12, which is corrected when intrinsic factor is administered with radioactive B12, since the vitamin can then be normally absorbed. 

A 63-year-old man with type 2 diabetes, who had taken metformin for at least 5 years, had a low serum vitamin Bi2 concentration (110 pg/ml reference range 200-230) and a normal serum folate (90). There were no autoantibodies. A Schilling test showed malabsorption of vitamin Bi2. Metformin was withdrawn and 2 months later a Schilling test showed no malabsorption. 

Vitamin B12 deficiency also occurs when the region of the distal ileum that absorbs the vitamin B12-intrinsic factor complex is damaged, as when the ileum is involved with inflammatory bowel disease, or when the ileum is surgically resected. In these situations, radioactively labeled vitamin B12 is not absorbed in the Schilling test, even when intrinsic factor is added. Other rare causes of vitamin B,2 deficiency include bacterial overgrowth of the small bowel, chronic pancreatitis, and thyroid disease. Rare cases of vitamin B12 deficiency in children have been found to be secondary to congenital deficiency of intrinsic factor and congenital selective vitamin Bi2 malabsorption due to defects of the receptor sites in the distal ileum. 

It is usual to give a test dose of between 0.5 and 1.0 pg of the labeled vitamin for the standard Schilling test, and in the case of the dual-isotope technique 0.25 pg each of 57Co- and 58Co-labeled vitamin. It has been found... 

B21. Brugge, W. R., Goff, J. S., Allen, N. C., Podell, E. R., and Allen, R. H., Development of a dual label Schilling test for pancreatic exocrine function based on the differential absorption of cobalamin bound to intrinsic factor and R protein. Gastroenterology 78, 937-949 (1980). 

Although these have been linked to malabsorption of B12 (e.g., cause abnormal Schilling tests), they have not been associated with megaloblastic anemia or neuropsychiatric diseases. Intrinsic factor is normally secreted in amounts greatly in excess of normal requirements, so that so that a 90% reduction in intrinsic factor secretion may be of little or no consequence. 

Absorption of vitamin B12 can be investigated in several ways after oral delivery of radioactive vitamin B12 (e.g. containing Co) and subsequent measurement of radioactivity in faecal excretion, whole body counting or liver uptake, plasma radioactivity or the popular Schilling test. For the Schilling test, urinary excretion of radioactive vitamin B12 is measured 24 h following oral delivery, and impaired absorption may indicate intrinsic factor deficiency bacterial colonization of the small intestine (stagnant gut syndrome) or ileal disease. 

The absorption of vitamin B12 can be determined by the Schilling test. An oral dose of [ Co] or [ Co]vitamin B12 is given with a parenteral flushing dose of 1 mg of nonradioactive vitamin, and the urinary excretion of radioactivity is followed as an index of absorption of the oral material. Normal subjects excrete 16% to 45% of the radioactivity over 24 hours, whereas patients lacking intrinsic factor or with antiintrinsic factor antibodies excrete less than 5%. 

Atrophic gastritis will cause decreased secretion of gastric acid before there is any impairment of intrinsic factor secretion. This means that the absorption of crystalline vitamin B12, as used in the Schilling test, is normal but the absorption of protein-bound vitamin B12 from foods will be impaired (Section 10.7.1), and the Schilling test will give a false-negative result. 

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