This test may be perfomed in four different stages to find the cause of low vitamin B12 levels.  Stage I is as described above. If Stage I is abnormal, Stage II may be done 3 to 7 days later. In Stage II, patients receive radioactive B12 along with intrinsic factor. Intrinsic factor is produced in the stomach and binds to vitamin B12.  Stage II can tell whether low vitamin B12 levels are caused by problems in the stomach that prevent it from producing intrinsic factor. If a Stage II test is abnormal, a Stage III test is performed. Here, the Stage II test is repeated after the patent has taken antibiotics for two weeks, and can tell whether the abnormal growth of bacterial has led to low vitamin B12 levels. A Stage IV test determines whether low vitamin B12 levels are caused by problems with the pancreas.  Here, the patient is given pancreatic enzymes for three days, followed by a radioactive dose of vitamin B12.

A 24-hour urine sample is needed. For adults:

• on day 1, urinate into the toilet after getting up in the morning.
• collect all subsequent urine (in a special container) for the next 24 hours.
• on the morning of day 2, urinate into the container after getting up.
• the test is now complete.
• cap the container. Keep it in the refrigerator or a cool place while uring is being collected.
• label the container with your name, the date, the time you last urinated, and return it as instructed.

For infants:

• thoroughly wash the area around the urethra.
• open a urine collection bag (a plastic bag with an adhesive paper on one end), and place it on your infant.
• for males, the entire penis can be placed in the bag and the adhesive attached to the skin. For females, the bag is placed over the labia.
• place a diaper over the infant (bag and all). The infant should be checked frequently and the bag changed after the infant has urinated into the bag. For active infants, this procedure may take a couple of attempts--lively infants can displace the bag, causing an inability to obtain the specimen.
• drain the urine into the container.
• deliver the container to the laboratory or your health care provider as soon as possible upon completion.

How to Prepare for the Test

• Fast (except for water) for 8 hours before starting the test, then eat normally for the next 24-hours.
• The health care provider may advise you to discontinue drugs that can affect the test.
• There must be no parenteral (intramuscular injection) B12 given within 3 days prior to the exam.
• If the collection is being taken from an infant, a couple of extra urine collection bags may be necessary.

How the Test will Feel

The injection of vitamin B12 may sting.

Why the Test is Performed

The Schilling test is performed to evaluate vitamin B12 absorption.

Intrinsic factor is produced in the stomach and is required for vitamin B12 absorption. If intrinsic factor is not made, the body cannot absorb vitamin B12. Low vitamin B12 levels can occur from the lack of intrinsic factor because of pernicious anemia, gastrectomy (partial removal of stomach), inadequate absorption due to bowel disease, bacterial overgrowth in the intestine, pancreatic insufficiency or certain medications. The Schilling test is most commonly used to evaluate patients for pernicious anemia.

The test can be falsely positive. Most of the time this is due to inadequate urine collection. Other reasons include kidney disease or problems with the lining of the small intestine.

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