The Schilling test is used to determine the cause of a vitamin B12 deficiency, which can result from lack of intrinsic or extrinsic factors or malabsorption in the ileum. Absorption of this vitamin requires that it be bound to intrinsic factor, a glycoprotein secreted by the gastric mucosa. Pernicious anemia, the most common and severest form of vitamin B12 deficiency, involves a deficiency of intrinsic factor, which reduces absorption of the vitamin in the ileum. Intestinal malabsorption syndrome, pancreatic disorders, and medications can also cause this vitamin deficiency.
The test involves the oral administration of a capsule of vitamin B12 labeled with the radioactive substance cobalt as cyanocobalamin Co 57 to determine gastrointestinal absorption of the vitamin. An injection of a nonradioactive vitamin B12 can be given in addition to the oral dose to enhance saturation of binding sites, intestinal absorption, and renal excretion of the radionuclide. A 24-hour urine specimen is then collected. Test results are expressed as the percentage of radionuclide excreted in the urine in relation to the amount administered. If less than 5 to 15 percent of the radionuclide is excreted, a two-stage test is indicated. For the second phase, an oral dose of intrinsic factor is given in addition to the labeled and unlabeled doses of the vitamin. If subsequent excretion of vitamin B12 reaches normal levels, pernicious anemia is confirmed; if not, malabsorption syndrome is present.79
Nursing Alert
- Urine collection time can be prolonged to 48 to 72 hours in clients with severe renal disease. The normal percentage of the labeled vitamin B12 will eventually be excreted, however, as long as the client does not have impaired vitamin B12 absorption.
Nursing Care Before the Procedure
Client preparation is the same as for any nuclear laboratory study (see section under "Total Blood Volume Study").
- Inform the client that a radioactive vitamin B12 is administered orally and a nonradioactive vitamin B12 is administered IM for the test and that the substances are eliminated from the body without harmful effects.
- Advise the client that food and fluid are withheld for 8 hours and that laxatives should be avoided for at least 2 days before the study.
- Provide a schedule for both administrations of the B12 and for urine collection, and provide a container to collect the urine.
- Inform and instruct the client in the collection of the urine specimen, including the length of time (usually 24 hours), care of the special container, importance of saving all the urine, and avoidance of contamination with feces or toilet tissue (see Appendix II).
- History should include information about hematologic and gastrointestinal status, results of folate, total binding capacity, B12 blood tests, and signs and symptoms of anemia or malabsorption.
One-Stage Test. The client voids and the urine is discarded. If a radionuclide study has been performed recently, a sample of the urine to be discarded can be sent to the laboratory for radioactivity residual. A 0.5- to 1.0-mg capsule of labeled vitamin B12 is administered orally. This dose is followed by an IM dose of 1000 mg of unlabeled B12 1 to 2 hours later (depending on laboratory preference). Foods and fluids can be resumed after the IM injection. All urine is collected for 24 hours in a container without a preservative (48 to 72 hours in those with renal disease) and sent to the laboratory for analysis (see Appendix II). When absorption is normal, vitamin B12 in excess of body needs is excreted by the kidneys. If absorption is impaired, the vitamin either does not appear in the urine or is found in only limited amounts. The unabsorbed B12 is excreted in the feces.
Two-Stage Test. The client voids and the urine is discarded. If the test is performed on the day after a one-stage test, a specimen from the first morning voiding should be checked by the laboratory for persistent radioactivity. A 0.5- to 1.0-mg capsule of labeled vitamin B12 is administered orally. The client can then eat breakfast, after which a 60-mg dose of intrinsic factor is administered orally. In 1 to 2 hours, an IM dose of 1000 mg of unlabeled vitamin B12 is administered ("flushing dose"). This dose competes with the absorbed radioactive material for binding sites and allows excretion of the radioactive B12 in the urine. All urine is collected for 24 hours in a container as in the one-stage test. Findings are based on the amount of B12 excreted in the urine over a specific period.
Nursing Care After the Procedure
Care and assessment after the test are the same as for any nuclear laboratory test (see section under "Total Blood Volume Study").
- Resume normal dietary intake.
- Assess for fatigue, weakness, sore tongue, anorexia, vomiting, or abdominal pain indicating pernicious anemia.
