A Schilling 24-hour urine test is done to evaluate whether vitamin B12 is being absorbed by the body. It is usually done when the results of a vitamin B12 blood test are low. The body needs this B vitamin to make blood cells and to maintain a healthy nervous system.

A lack of vitamin B12 can be caused by a lack of the vitamin in the diet or, more commonly, by a problem with absorbing the vitamin from the intestines. A substance made in the stomach called intrinsic factor helps the intestines absorb vitamin B12. If the intrinsic factor is not present, vitamin B12 may not be absorbed properly.

A Schilling test may be given in two parts. Part one measures the amount of vitamin B12 passed in urine after a known amount of the vitamin tagged with a radioactive substance is swallowed. If the intestines absorb vitamin B12 normally, a certain amount of the vitamin (up to 25% of the amount swallowed) will be passed in the urine. If the intestines cannot absorb the vitamin normally, very little or no vitamin B12 will be present in the urine.

A Schilling test with abnormal results (no vitamin B12 in the urine) may be repeated after giving an oral dose of intrinsic factor and radioactive B12. This is called part two of the test, and it tells whether the vitamin deficiency is caused by a lack of intrinsic factor or from a problem with the intestines.

Why It Is Done

The Schilling test is done to:

• Determine the cause of a low level of vitamin B12.
• Check for vitamin B12 deficiency anemia in people at high risk for developing this anemia, such as those who have had stomach or intestinal surgery, small intestine problems, or people with a family history of this anemia.
• Help diagnose pernicious anemia, a serious blood disease caused by a lack of intrinsic factor.

How To Prepare

Do not eat or drink (except water) for 10 to 12 hours before this test. Do not take any supplements containing vitamin B12 for at least three days before having the Schilling test. Also, do not use laxatives for 24 hours before the test.

Talk to your health professional about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).