The Schilling test is used to determine whether the body absorbs vitamin B12 normally.

You will get 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. Your urine will then be collected over the next 24 hours to measure whether you are absorbing vitamin B12 normally.

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 - 7 days later. In Stage II, you'll receive radioactive B12 along with intrinsic factor.

Intrinsic factor is produced in the stomach and attaches (binds) to vitamin B12. Stage II of the test 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.

In the Stage III test, the Stage II test is repeated after you have taken antibiotics for 2 weeks. This can tell whether abnormal bacterial growth has caused the low vitamin B12 levels.

A Stage IV test determines whether low vitamin B12 levels are caused by problems with the pancreas. With this test, you will take 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 of your 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.
• Label the container with your name, the date, and the time you last urinated, and return it as instructed.

For infants:

• Thoroughly wash the area around the area from which urine exits the body (urethra).
• Open a urine collection bag (a plastic bag with an adhesive paper on one end), and place it on your infant.
• For males, place the entire penis in the bag and attach the adhesive to the skin. For females, place the bag over the labia.
• Place a diaper over the infant (including the bag). Check the infant often and change the bag after the infant has urinated into it. For active infants, this procedure may take a couple of attempts -- lively infants can displace the bag, making it difficult to get the urine sample.
• Drain the urine into the container.
• Deliver the container to the laboratory or your health care provider as soon as possible after you've collected all of the urine.

• Fast (you can drink water) for 8 hours before starting the test, then eat normally for the next 24 hours.
• The health care provider may ask you to stop taking drugs that can affect the test.
• You cannot have parenteral (intramuscular injection) B12 within 3 days before the exam.
• If the collection is being taken from an infant, you may need to use a couple of extra urine collection bags.

The injection of vitamin B12 may sting.