The Schilling test is a medical procedure that tests how well the body will absorb vitamin B12. It helps evaluate patients for certain conditions that alter B12 absorption such as pernicious anemia, B12 deficiency anemia, blind loop syndrome, and megaloblastic anemia.
Stage One
In this stage, the patient takes a small dose of a radioactive form of B12 orally. A second dose that is bigger than the first will be done an hour later as an injection. The patient then does a 24 hour urine collection and the laboratory will check this sample to view vitamin absorption.
Stage Two
Stage two is done three to seven days after the first stage, if there is abnormal results from it. Along with the same radioactive B12 you are given intrinsic factor, a protein from stomach lining cells. This tells the doctor if it is the B12 level problems are caused by the stomach preventing the production of intrinsic factor.
Stage Three
Stage three is done if the stage two results are abnormal. You take antibiotics for two weeks during this stage, telling the doctor if abnormal bacteria growing in the body causes the B12 level reduction.
Stage Four
Stage four is where the patient takes three days of pancreatic enzymes and then a dose of radioactive B12. This tells the doctor if the low levels of B12 are from pancreas problems.
Abnormal Results
Abnormal low vitamin B12 results can be from biliary disease, liver disease, pancreatic disease, celiac disease, or from Crohn’s disease.
Source: A.D.A.M.