Alternate Names: Vitamin B12 absorption test

How Performed:

The patient is given an oral dose of radioactive B12 (cobalamin). An intramuscular injection of nonradioactive vitamin B12 is given 2-6 hours after the oral dose is administered which will bind all available vitamin B12 receptor sites (that is, places on cells that combine with and hold B12). The injection of vitamin B12 may sting. This injection, however, will facilitate rapid excretion of the radioactive vitamin B12 because there are no places in the body for it to adhere. By collecting the urine, urinary B12 levels are then measured over the next 24 hours. Intrinsic factor is a gastric substance that binds with vitamin B12 and allows it to be absorbed.

There are four possible stages to the Schilling test to pinpoint the cause of B12 deficiency. Stage I is as described above. Three to seven days later, Stage II is performed if Stage I is abnormal. Stage II is radioactive B12 co-administered with intrinsic factor. If Stage II is abnormal, a Stage III test is performed. This entails treatment with antibiotics for two weeks and then the Stage II test is repeated. If the test result normalizes, bacterial overgrowth of the gut is suspected. Stage IV involves administering radioactive B12 after the patient has been given pancreatic enzymes for three days. If the B12 deficiency is due to pancreatic insufficiency, the test result should normalize.

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

• on day 1, urinate into the toilet upon arising in the morning.
• collect all subsequent urine (in a special container) for the next 24-hours.
• on day 2, urinate into the container in the morning upon arising.

Cap the container. Keep it in the refrigerator or a cool place during the collection period.

• label the container with your name, the date, the time of completion, 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.
• the urine is drained into the container for transport to the laboratory.
• deliver it to the laboratory or your health care provider as soon as possible upon completion.

How To Prepare:

• 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 It Feels: The injection of vitamin B12 may sting.

Risks:

• local reaction to injection of vitamin
• nausea
• feeling lightheaded

Why Performed:

The Schilling test is performed to evaluate vitamin B12 absorption. Normally, ingested vitamin B12 combines with intrinsic factor, which is produced by cells in the stomach. Intrinsic factor is necessary for vitamin B12 absorption in the distal part of the ileum (middle part of the small intestine).

The causes of B12 deficiency include absence of intrinsic factor either due to pernicious anemia or 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.

There can be false positive results. The most common reason for this is inadequate urine collection. Other reasons include renal failure and dysfunction of the lining of the small intestine secondary to B12 deficiency.

Some physicians have questioned the use of a Schilling test, as it often does not alter clinical management. The test, however, can be used to confirm a diagnosis of pernicious anemia. Also, a normal Schilling test may indicate a dietary deficiency of B12.

Normal Values: Excretion of 8 to 40% of the radioactive vitamin B12 within 24-hours is normal.

Abnormal Results: Pernicious anemia results when absorption of vitamin B12 is inadequate. This may be caused by a primary malabsorption problem; possibly caused by an inflammation in the intestines, a deficiency of vitamin B12 in the diet, or a deficiency of intrinsic factor. The most common cause of intrinsic factor deficiency is surgical resection of part of the stomach as treatment for peptic ulcer. Other causes include genetic deficiency and development of an antibody that reacts against the intrinsic factor. Patients who have pernicious anemia from lack of intrinsic factor will have abnormal results on the 1-stage Schilling test (that is, the first test with out intrinsic factor) and normal results when on 2-stage Schilling test (that is, the second test performed about 1 week after the first and after intrinsic factor is given). Patients with malabsorption from an intestinal source will have abnormal results from both the 1- and 2-stage Schilling tests.

Abnormal 1- and 2-stage Schilling tests may indicate:

• biliary disease
• celiac disease (sprue)
• hypothyroidism
• liver disease

• biliary disease, resulting in malabsorption (inadequate absorption of nutrients from the intestinal tract)
• intestinal malabsorption (for example, related to sprue or celiac disease)
• liver disease (causing malabsorption)
• pernicious anemia

• anemia of B12 deficiency
• blind loop syndrome
• megaloblastic anemia

Cost:

Special Considerations: