Vitamin B12 absorption test
The Schilling test is used to determine whether Vitamin B12 is absorbed normally by the body.
How the test is performed
The patient is given two doses of Vitamin B12 (cobalamin). The first dose is radioactive and taken by mouth. The second dose is not radioactive and is given as a shot 2-6 hours later. The injection of Vitamin B12 may sting. Urine is then collected over the next 24 hours to measure whether Vitamin B12 is normally absorbed.
This test may be performed 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 urine is being collected.
- Label the container with your name, the date, the time you last urinated, and return it as instructed.
- 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.
Excretion of 8 to 40% of the radioactive Vitamin B12 within 24-hours is normal.
What abnormal results mean
Low vitamin B12 levels can cause pernicious anemia. This can be caused by problems absorbing Vitamin B12 or not eating enough foods that contain Vitamin B12. Some other causes are removal of part of the stomach or the development of an antibody against intrinsic factor. If there is a problem with the stomach’s ability to make intrinsic factor, Stage I of the test will be abnormal and Stage II will be normal. Both the Stage I and II Schilling tests will be abnormal in patients who have problems absorbing Vitamin B12 and intrinsic factor in the small intestine.
Abnormal Stage I and II Schilling tests may indicate:
- biliary disease
- celiac disease (sprue)
- liver disease
Lower-than-normal amounts of Vitamin B12 absorption may indicate:
- 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
Additional conditions under which the test may be performed:
- anemia of B12 deficiency
- blind loop syndrome
- megaloblastic anemia
What the risks are
- local reaction to injection of vitamin
- feeling lightheaded
by Sharon M. Smith, M.D.