Briefly describe how the Schilling test is performed.

The Schilling test is a diagnostic test used to determine the cause of vitamin B12 deficiency. It involves giving the patient a small amount of radioactive vitamin B12 orally, followed by an injection of non-radioactive vitamin B12. The amount of radioactive vitamin B12 excreted in the urine is then measured to determine the body's ability to absorb and utilize the vitamin.

Schilling Test

Procedure:

1. Prepare the patient: Patient fasts overnight and receives an intramuscular injection of intrinsic factor.
2. First dose: A capsule containing radioactive vitamin B12 is administered orally.
3. Urine collection: Urine is collected for 24 hours and a sample is analyzed to determine the amount of radioactive B12 excreted.
4. Second dose: A second capsule containing non-radioactive vitamin B12 is administered orally.
5. Additional urine collection: Urine is collected for an additional 24 hours and analyzed for radioactive B12 excretion.

Interpretation:

- Normal: ≥25% of the radioactive B12 excreted in the first 24-hour urine collection and ≥15% more excreted after the second dose.
- Abnormal: Decreased or absent radioactive B12 excretion indicates a deficiency in intrinsic factor or malabsorption of vitamin B12.