Vitamin B12 deficiency schilling test

Schilling Test

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

phase 1: oral vitamin B₁₂ and intramuscular vitamin B₁₂

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.

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

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

Useful for identifying patients with bacterial overgrowth syndrome.

Phase 4: vitamin B₁₂ and pancreatic enzymes

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
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.