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The Schilling test is used to determine whether the body absorbs vitamin B12 normally.
Vitamin B12 absorption test
How the Test is Performed
This test may be done in four different stages to find the cause of a low vitamin B12 level.
Stage I: You get two doses of vitamin B12 (cobalamin). You take a small, first dose (a radioactive form of B12) by mouth. You get a second, larger dose by a shot 1 hour later. You then collect your urine over the next 24 hours and deliver it to a lab or your doctor's office. The urine is checked to see if you are absorbing vitamin B12 normally. If Stage I is abnormal, Stage II may be done 3 to 7 days later.
Stage II: You are given radioactive B12 along with intrinsic factor. Intrinsic factor is a protein produced by cells in the stomach lining. The body needs it so the intestines can absorb vitamin B12.
Stage II of the test can tell whether a low vitamin B12 level is caused by problems in the stomach, preventing it from producing intrinsic factor.
If Stage II is abnormal, a Stage III test is done.
Stage III: This test is done after you have taken antibiotics for 2 weeks. It can tell whether abnormal bacterial growth has caused the low vitamin B12 levels.
Stage IV: This test determines whether low vitamin B12 levels are caused by problems with the pancreas. With this test, you take pancreatic enzymes for 3 days. You then take a radioactive dose of vitamin B12.
How to Prepare for the Test
- Do not eat for 8 hours before starting the test, then eat normally for the next 24 hours. You can drink water.
- The health care provider may ask you to stop taking medicines that can affect the test.
- You cannot have intramuscular injection B12 within 3 days before the test.
How the Test will Feel
The injection of vitamin B12 may sting.
Why the Test is Performed
The Schilling test checks vitamin B12 absorption and evaluates you for pernicious anemia. This is a decrease in red blood cells that occurs when your intestines cannot properly absorb vitamin B12.
Other conditions for which the test may be performed:
Urinating 8% to 40% of the radioactive vitamin B12 within 24 hours is normal.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
Low vitamin B12 levels can cause megoblastic anemia.
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.
Stages I and II will be abnormal in people who have problems absorbing vitamin B12 and intrinsic factor in the small intestine.
Abnormal results may be due:
- Local reaction to vitamin injection
- Feeling light-headed
Antony AC. Megaloblastic anemias. In: Hoffman R, Benz EJ Jr, Silberstein LE, et al., eds. Hematology: Basic Principles and Practice. 6th ed. Philadelphia, Pa: Elsevier Saunders; 2012:chap 37.
Elghetany MT, Banki K. Erythrocytic disorders. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 32.
Hogenauer C, Hammer HF. Maldigestion and malabsorption. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease Pathophysiology/Diagnosis/Management. 9th ed. Philadelphia, Pa: Elsevier Saunders; 2010:chap 101.
Reviewed By: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.