Schilling test

The Schilling's test is a medical investigation used in patients with vitamin Bssub|12 deficiency.cite journal |author=Zuckier LS, Chervu LR |title=Schilling evaluation of pernicious anemia: current status |journal=Journal of nuclear medicine : official publication, Society of Nuclear Medicine |volume=25 |issue=9 |pages=1032–9 |year=1984 |month=September |pmid=6470805 |doi= |url=http://jnm.snmjournals.org/cgi/pmidlookup?view=long&pmid=6470805] The purpose of the test is to determine if the patient has pernicious anemia.

It is named for Robert F. Schilling.cite web |url=http://medical.merriam-webster.com/medical/schilling%20test |title=Schilling+test - Definition from Merriam-Webster's Medical Dictionary |format= |work= |accessdate=2008-10-05]

Process

There are a few variations on the exact procedure used.

In the first part of the test, the patient is given radiolabeled vitamin Bssub|12 to drink. The most commonly used radiolabels are ⁵⁷Co and ⁵⁸Co. An intramuscular injection of unlabeled vitamin Bssub|12 is given at around the same time. The purpose of this injection is to saturate tissue stores with normal vitamin Bssub|12 to prevent radioactive vitamin Bssub|12 binding in body tissues, so that if absorbed, it will pass into the urine. The patient's urine is then collected over the next 24 hours to assess the absorption.

Normally, the ingested radiolabeled vitamin Bssub|12 will be absorbed into the body. Since the body already has liver receptors for transcobalamin/vitamin Bssub|12 saturated by the injection, much of the ingested vitamin Bssub|12 will be excreted in the urine.

A normal result shows at least 5% of the radiolabelled vitamin Bssub|12 in the urine over the first 24 hours. In patients with pernicious anemia or with deficiency due to impaired absorption, less than 5% of the radiolabeled vitamin Bssub|12 is detected.

If an abnormality is found, 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, or pernicious anemia. A low result on the second test implies abnormal intestinal absorption (malabsorption), which could be caused by coeliac disease, biliary disease, Whipple's disease, fish tapeworm infestation (Diphyllobothrium latum), or liver disease. Malabsorption of Bssub|12 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.

In some versions of the Schilling's test, Bssub|12 can be given both with and without intrinsic factor at the same time, using different cobalt radioisotopes ⁵⁷Co and ⁵⁸Co, which have different radiation signatures, in order to differentiate the two forms of Bssub|12. This allows for only a single radioactive urine collection.

Note that the Bssub|12 shot which begins the Schilling's test is enough to go a considerable way toward treating Bssub|12 deficiency, so the test is also a partial "treatment" for Bssub|12 deficiency. Also, the classic Schilling test can be performed at any time, even after full Bssub|12 repletion and correction of the anemia, and it will still show if the cause of the Bssub|12 deficiency was intrinsic-factor related. In fact, some clinicians have suggested that full folate and Bssub|12 replacement be normally performed "before" a Schilling's test is done, since folate and Bssub|12 deficiencies are both known to interfere with intestinal cell function, and thus cause malabsorption of Bssub|12 on their own, even if intrinsic factor is being made. This state would then tend to cause a false-positive test for intrinsic factor-related Bssub|12 malabsorption.

Many labs have stopped performing the Schilling's test, due to lack of production of the cobalt radioisotopes and labeled-Bssub|12 test substances.

Diagnoses

References

External links

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