Vitamin B12 deficiency schilling test

## Overview

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## Schilling Test

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The Schilling test is used to diagnose the site of the disorder causing cobalamin deficiency.

### phase 1: oral vitamin B12 and intramuscular vitamin B12

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Patient is taken 1 µg of radioactive B12 orally then An intramuscular injection of unlabeled vitamin B12 is given an hour later. Single intramuscular injection is given due to temporarily saturate B12 receptors in the liver with  to prevent radioactive vitamin B12 binding in body tissues (especially in the liver), if it absorbed from the G.I. tract, it will pass into the urine. The patient's urine is collected over the next 24 hours to assess the absorption.[1]

Normally, the ingested radiolabeled vitamin B12 will be absorbed into the body. Since the body already has liver receptors for transcobalamin/vitamin B12 saturated by the injection, much of the ingested vitamin B12 will be excreted in the urine.

* A normal result shows at least 10% of the radiolabeled vitamin B12 in the urine over the first 24 hours.
* In patients with pernicious anemia or with deficiency due to impaired absorption, less than 10% of the radiolabeled vitamin B12 is detected.

The normal test will result in a higher amount of the radiolabeled cobalamin in the urine because it would have been absorbed by the intestinal epithelium, but passed into the urine because all hepatic B12 receptors were occupied. 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.

### Phase 2: vitamin B12 and intrinsic factor

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If B12 in the urine is low , the test is repeated, this time with additional oral intrinsic factor.

* If this second urine collection is normal, this shows a lack of intrinsic factor production. This is by definition pernicious anemia.
* A low result on the second test implies abnormal intestinal absorption (malabsorption), which is due to coeliac disease, biliary disease, Whipple's 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

### Phase 3: vitamin B12 and antibiotics

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Useful for identifying patients with bacterial overgrowth syndrome.

### Phase 4: vitamin B12 and pancreatic enzymes

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In this phase pancreatic enzymes are administered, useful to identifying patients with pancreatitis

Test  | Gastrectomy, pernicious anemia  | Celiac disease*  | Bacterial overgrowth  | Ileal resection or disease•  | Pancreatic insufficiency

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Vitamin B12  | Low  | Low  | Low  | Low/normal  | Low
Vitamin B12 + intrinsic factor  | Normal  | Low  | Low  | Low/normal  | Low
Vitamin B12 + antibiotics  | n/a  | Low  | Normal  | Low/normal  | Low
Vitamin B12 + gluten-free diet  | n/a  | Normal  | n/a  | Low/normal  | Low
Vitamin B12 + pancreatic enzymes  | n/a  | n/a  | n/a  | n/a  | Normal

* The Schilling test may be normal in patients with celiac disease because the terminal ileum is frequently spared. n/a, these stages of the Schilling test are not needed for the disorder.

• Results depend upon the length of resection or the extent of disease. Values will not normalize with >100 cm of resection. Values may normalize after treatment of active Crohn's disease.

## References

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1. ↑ MacFarlane AJ, Greene-Finestone LS, Shi Y (October 2011). "Vitamin B-12 and homocysteine status in a folate-replete population: results from the Canadian Health Measures Survey". Am. J. Clin. Nutr. 94 (4): 1079–87. doi:10.3945/ajcn.111.020230. PMID 21900461.

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