Note that the B shot which begins the Schilling test is enough to go a considerable way toward treating B deficiency, so the test is also a partial treatment for B deficiency. Also, the classic Schilling test can be performed at any time, even after full B repletion and correction of the anemia, and it will still show if the cause of the B deficiency was intrinsic-factor related. In fact, some clinicians have suggested that folate and B replacement for several weeks be normally performed before a Schilling test is done, since folate and B deficiencies are both known to interfere with intestinal cell function, and thus cause malabsorption of B on their own, even if intrinsic factor is being made. This state would then tend to cause a false-positive test for both simple B and intrinsic factor-related B malabsorption. Several weeks of vitamin replacement are necessary, before epithelial damage to the G.I. tract from B deficiency is corrected.
Many labs have stopped performing the Schilling test, due to lack of production of the cobalt radioisotopes and labeled-B test substances. Also, injection replacement of B has become relatively inexpensive, and can be self-administered by patients, as well as megadose oral B. Since these are the same treatments which would be administered for most causes of B 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 B testing is not allowed to lapse).
It is possible for use of other radiopharmaceuticals to interfere with interpretation of the test.