Schilling Test for Absorption of Vitamin B12 (Cobalamin)

 

Patient preparation:

(1) overnight fast

(2) no recent vitamin B12 therapy

(3) no recent exposure to radiopharmaceutical agents

(4) The patient should not be pregnant.

 

Methodology - Stage 1

(1) A dose of radiolabeled vitamin B12 (using Cobalt-57) is administered orally.

(2) A large IM parenteral dose of vitamin B12 is given, sufficient to saturate hepatic uptake. This will result in any orally absorbed vitamin B12 being excreted in the urine.

(3) Urine is collected for 24 hours with the specimen kept refrigerated or on ice.

(4) The urine is then analyzed for total radioactivity.

 

percent absorbed and excreted =

= (total radioactivity in the urine) / (administered radioactivity) * 100%

 

Methodology - Stage 2:

(1) Wait at least 5 days after Stage 1.

(2) As for stage 1, except that the oral dose of radiolabeled vitamin B12 is administered with intrinsic factor.

 

Cautions when doing the test:

(1) Do not collect samples for other RIA analysis after administration of the radioactive vitamin B12 for several days.

(2) Incomplete urine collections can result in falsely low values of urinary vitamin B12 excretion.

(3) Fecal contamination in urine sample may cause a falsely high value of urinary vitamin B12 excretion.

 

Interpretation:

• Normally > 10% of the administered dose of radioactive vitamin B12 should be excreted in the urine.

Stage 1	Stage 2	Interpretation
normal	NA	normal absorption; dietary deficiency or failure of vitamin B12 to dissociate from food
abnormal	normal	lack of intrinsic factor (pernicious anemia, gastric resection, synthesis of a defective protein)
abnormal	abnormal	bacterial overgrowth, pancreatic insufficiency, malabsorption due to ileal defect, fish tapeworm (Diphyllobothrium latum)

 

 

Testing Variations	Reason
vitamin B12 after therapy with a course of oral tetracycline (Stage 3)	bacterial overgrowth syndrome
vitamin B12 with administration of pancreatic extract	pancreatic insufficiency
increased time period for the urine collection	renal insufficiency (normal absorption but delayed excretion)