Complications
Note that the B12 shot which begins the Schilling test is enough to go a considerable way toward treating B12 deficiency, so the test is also a partial treatment for B12 deficiency. Also, the classic Schilling test can be performed at any time, even after full B12 repletion and correction of the anemia, and it will still show if the cause of the B12 deficiency was intrinsic-factor related. In fact, some clinicians have suggested that folate and B12 replacement for several weeks be normally performed before a Schilling test is done, since folate and B12 deficiencies are both known to interfere with intestinal cell function, and thus cause malabsorption of B12 on their own, even if intrinsic factor is being made. This state would then tend to cause a false-positive test for both simple B12 and intrinsic factor-related B12 malabsorption. Several weeks of vitamin replacement are necessary, before epithelial damage to the G.I. tract from B12 deficiency is corrected. Many labs have stopped performing the Schilling test, due to lack of production of the cobalt radioisotopes and labeled-B12 test substances. Also, injection replacement of B12 has become relatively inexpensive, and can be self-administered by patients, as well as megadose oral B12. Since these are the same treatments which would be administered for most causes of B12 malabsorption even if the exact cause were identified, the diagnostic test may be omitted without damage to the patient (so long as follow-up treatment and occasional serum B12 testing is not allowed to lapse).
A low result on the second test implies abnormal intestinal absorption (malabsorption), which could be caused by coeliac disease, biliary disease, Whipples disease, small bowel bacterial overgrowth syndrome, fish tapeworm infestation (Diphyllobothrium latum), or liver disease. Malabsorption of B12 can be caused by intestinal dysfunction from a low vitamin level in-and-of-itself (see below), causing test result confusion if repletion has not been done for some days previously. Stage 3: vitamin B12 and antibiotics
This stage is useful for identifying patients with bacterial overgrowth syndrome. The physician will provide you a course of 2 weeks of antibiotics to eliminate any possible bacterial overgrowth and repeat the test to check whether radio-labeled Vitamin B12 would be found in urine or not. Stage 4: vitamin B12 and pancreatic enzymes
This stage, in which pancreatic enzymes are administered, can be useful in identifying patients with pancreatic insufficiency. The physician will give you 3 days of pancreatic enzymes followed by repeating the test to check if radio-labeled Vitamin B12 would be detected in urine. Combined stage 1 and stage 2
In some versions of the Schilling test, B12 can be given both with and without intrinsic factor at the same time, using different cobalt radioisotopes 57Co and 58Co, which have different radiation signatures, in order to differentiate the two forms of B12. This is performed with the Dicopac kitset. This allows for only a single radioactive urine collection.