The Schilling test (synonym: urine excretion test according to Schilling) is a diagnostic procedure in nuclear medicine that can be used to determine the uptake of vitamin B12. With the help of the Schilling test, it is possible to draw conclusions about the cause of an existing vitamin B12 deficiency on the basis of the result. The Schilling test can be carried out both with the addition of intrinsic factor (a factor formed in the stomach‘s vestibular cells that enables vitamin B12 to be absorbed in the small intestine) and without the addition of the factor. Based on the test results without and with the addition of intrinsic factor, a resorption disorder due to a deficiency or loss of function of intrinsic factor can be distinguished from a disease of the terminal ileum (small intestine portion – resorption site of vitamin B12).
Indications (areas of application)
- Pernicious anemia – this form of anemia (anemia) is caused by autoimmune deficiency of intrinsic factor, which leads to reduction of serum vitamin B12. Vitamin B12 is of particular importance in DNA synthesis, so as a result of a deficiency, macrocytic anemia (synonym: megaloblastic anemia; hyperchromic macrocytic anemia; as a result of vitamin B12, thiamine or folic acid deficiency, red blood cell production is reduced) develops. In addition, neurological symptoms occur, also known as funicular myelosis (synonym: funicular spinal disease; demyelinating disease (degeneration of the posterior cord, lateral cord, and a polyneuropathy/diseases of the peripheral nervous system affecting multiple nerves); symptomatology: deficits of motor function and sensitivity that may worsen to paraplegia; encephalopathy (pathological conditions of the brain) of varying degrees). The cause of the occurrence of pernicious anemia represents the formation of auto-antibodies against the occupational cells and intrinsic factor in the context of chronic autoimmune gastritis. When performing the Schilling test with the addition of intrinsic factor shows a normalized vitamin B12 uptake.
- Condition after partial gastric resection – removal of part of the stomach may result in inadequate release of the factor if the number of intrinsic factor-producing vestibular cells is too low, so that insufficient vitamin B12 can be absorbed in the terminal ileum. Changes in pH can also lead to reduced absorption of vitamin B12. When performing the Schilling test with the addition of the intrinsic factor also shows a normalized vitamin B12 uptake in this case.
- Dysfunction of intrinsic factor – in the presence of dysfunction of different genesis (origin) shows normal vitamin B12 intake when performing the Schilling test with the addition of intrinsic factor.
- Bacterial colonization of the small intestine – in the case of a bacterial overgrowth of the small intestine can not be achieved normal vitamin B12 uptake when performing the Schilling test with the addition of intrinsic factor, because even the added factor in the terminal ileum can not be absorbed.
- Chronic inflammation in the ileum – in the context of inflammatory bowel disease such as Crohn’s disease, vitamin deficiency symptoms often occur. However, the Schilling test is not normalized by the addition of intrinsic factor.
- Suspected malnutrition – the cause of vitamin B12 deficiency can also be a diet with reduced vitamin intake. Accordingly, when performing the Schilling test, a normalized test result can be achieved with the addition of the intrinsic factor.
Contraindications
Absolute contraindications
- Gravidity (pregnancy)
Before the examination
- Discontinuation of medications – due to an influence, all medications that may affect vitamin B12 absorption must be discontinued, if possible.
- Exclusion of previous administration of radioactive substances – before performing the Schilling test, an adequate time interval for the administration of radioactive substances and contrast media must be ensured in order to be able to exclude falsification of the measurement result.
- Food refrain – to be able to ensure a meaningful examination, the patient must appear fasting to the test performance.
- Application of radioactive vitamin B12 – after successful bladder emptying before the start of the test, the patient is orally administered 1 µg of radioactively labeled vitamin B12.
The procedure
Following the administration of the radioactive substance, the collection period of urine for 24 hours is started. For a period of 2 hours after ingestion of the radioactive vitamin B12, the patient must remain fasting. As a washout dose, 1,000 µg of cyanocobalamin (vitamin B12) is applied intramuscularly after 2 hours. For the evaluation of the Schilling test, the radioactivity is measured with the help of a scintillation counter in the 24-hour collection urine. Depending on the indication, the test may be performed with the addition of intrinsic factor.
After the examination
Adequate drinking of 1.5-2 l of fluid per day is important for elimination of radioactive vitamin B12.
Possible complications
Radiation exposure from the radioactive substance used is considered to be rather low. Nevertheless, the theoretical risk of radiation-induced late malignancy (leukemia or carcinoma) is increased, so a risk-benefit assessment should be performed. Due to reduced bladder emptying, radiation exposure can be significantly higher than in normal cases. Because of this, abnormalities of bladder emptying should be addressed, particularly in the medical history.
