[3] As noted below, it can be done at any time after vitamin B12 supplementation and body store replacement, and some clinicians recommend that in severe deficiency cases, at least several weeks of vitamin repletion be done before the test (more than one B12 shot, and also oral folic acid), in order to ensure that impaired absorption of B12 (with or without intrinsic factor) is not occurring due to damage to the intestinal mucosa from the B12 and folate deficiency themselves.
An abnormal result is caused by less of the labeled cobalamin to appear in the urine because it will remain in the intestine and be passed into the feces.
If an abnormality is found, i.e. the B12 in the urine is only present in low levels, the test is repeated, this time with additional oral intrinsic factor.
The physician will provide 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.
The physician will give 3 days of pancreatic enzymes followed by repeating the test to check if radio-labeled Vitamin B12 would be detected in urine.
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.
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.