- The Schilling test is used to evaluate the ability of the small intestine to absorb vitamin B12. When vitamin B12 is ingested, it combines with intrinsic factor from the gastric mucosa. It is then able to be absorbed in the ileum.
- This test involves the oral administration of radioactive vitamin B12. Nonradioactive vitamin B12 is then administered intramuscularly (IM) to saturate the vitamin B12 binding sites. A 24-hour urine specimen is collected.
- Normal patients will absorb and then excrete as much as 25% of the radioactive B12, since they have intrinsic factor and can thus absorb the vitamin from the gastrointestinal tract. Patients who have pernicious anemia, in which intrinsic factor is lacking, absorb little if any of the oral dose of B12, resulting in little or no radioactive material being excreted in the urine.
- If the results of the Schilling test show low absorption of the radioactive vitamin B12, the test is repeated along with intrinsic factor being given to rule out intestinal malabsorption. If the urinary excretion rises to normal levels, there is a lack of intrinsic factor. If urinary excretion remains low, malabsorption is probably the cause of the patient’s anemia.