Schilling Test – Indications, Procedures, Results

Vitamin B12 absorption test

The Schilling can determine whether the body absorbs vitamin B12 normally. It checks for certain types of anemia that are caused by a low vitamin B12 level.

A Schilling test is also known as a Vitamin B12 absorption test. It was formerly used to determine whether a person was absorbing vitamin B12 normally. If not, then the test could pinpoint the cause of any vitamin B12 deficiency. Schilling tests are no longer used today.

This test is rarely if ever, done today.

Process

The Schilling test has multiple stages.^[rx] As noted below, it can be done at any time after vitamin B₁₂ supplementation and body store replacement, and some clinicians recommend that in severe deficiency cases, at least several weeks of vitamin repletion be done before the test (more than one B₁₂ shot, and also oral folic acid), in order to ensure that impaired absorption of B₁₂ (with or without intrinsic factor) is not occurring due to damage to the intestinal mucosa from the B₁₂ and folate deficiency themselves.

Stage 1: oral vitamin B₁₂ plus intramuscular vitamin B12 (without IF)

In the first part of the test, the patient is given radiolabeled vitamin B₁₂ to drink or eat. The most commonly used radiolabels are Co and Co. An intramuscular injection of unlabeled vitamin B₁₂ is given an hour later. This is not enough to replete or saturate body stores of B₁₂. The purpose of the single injection is to temporarily saturate B₁₂ receptors in the liver with enough normal vitamin B₁₂ to prevent radioactive vitamin B₁₂ binding in body tissues (especially in the liver), so that if absorbed from the G.I. tract, 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 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 appearing in the urine because it will remain in the intestine and be passed into the feces.

Stage 2: vitamin B₁₂ and intrinsic factor

If an abnormality is found, i.e. the B12 in the urine is only present at low levels, the test is repeated, this time with an 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 could be caused by 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 in confusion if repletion has not been done for some days previously.

Stage 3: vitamin B₁₂ and antibiotics

This stage is useful for identifying patients with bacterial overgrowth syndrome. The physician will provide you a course of 2 weeks of antibiotics to eliminate any possible bacterial overgrowth and repeat the test to check whether radio-labeled Vitamin B12 would be found in urine or not.

Stage 4: vitamin B₁₂ and pancreatic enzymes

This stage, in which pancreatic enzymes are administered, can be useful in identifying patients with pancreatic insufficiency. The physician will give you 3 days of pancreatic enzymes followed by repeating the test to check if radio-labeled Vitamin B12 would be detected in urine.

Combined stage 1 and stage 2

In some versions of the Schilling test, B₁₂ 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 B₁₂. This is performed with the ‘Dicopac’ kitset. This allows for only a single radioactive urine collection.^[rx]

FAQ

Why is a Schilling test performed?

• Your doctor might have recommended the Schilling test if you had a vitamin B12 deficiency. The test can help them determine whether your stomach is producing an “intrinsic factor.” Intrinsic factor is a type of protein required for vitamin B12 absorption.

Which action does the Schilling test for pernicious anemia determine?

• The Schilling test measures cobalamin absorption by assessing increased urine radioactivity after an oral dose of radioactive cobalamin. The test is useful in demonstrating that the anemia is caused by an absence of IF and is not secondary to other causes of cobalamin deficiency (see the table below).

What is the test for pernicious anemia?

• People who have pernicious anemia have low reticulocyte counts. Serum folate, iron, and iron-binding capacity tests also can help show whether you have pernicious anemia or another type of anemia. Another common test, called the Combined Binding Luminescence Test, sometimes gives false results.

Which radioisotope is used for the Schilling test?

• The most commonly used radiolabels are ⁵⁷Co and ⁵⁸Co. An intramuscular injection of unlabeled vitamin B₁₂ is given an hour later.

Is the Schilling test a blood test?

• The Schilling test is no longer used to diagnose vitamin B12 deficiency. Nowadays, doctors diagnose vitamin B12 deficiency anemia through blood tests. These are sometimes called Cobalamin tests. From your blood sample, your doctor will assess the number and appearance of your red blood cells.

What is a shilling worth?

The twelve pence

• The shilling (1/- or 1s.) was a coin worth one-twentieth of a pound sterling, or twelve pence. It was first minted in the reign of Henry VII as the testoon and became known as the shilling, from the Old English spelling, sometime in the mid-16th century. It circulated until 1990.

How is a Schilling test performed?

• The patient is given radiolabeled vitamin B12 orally, followed by an intramuscular (IM) dose of unlabeled vitamin B12 one hour later. The injection is given to ensure that none of the radioactive B12 binds to any vitamin B12 depleted tissues, for example, the liver.

What is the B12 test called?

• When a B12 level is normal or low normal but a deficiency is still suspected, a healthcare practitioner may order a methylmalonic acid (MMA) test as an early indicator of B12 deficiency. A low B12 and/or folate level means that you have a deficiency.

How is B12 tested?

• How does the vitamin B-12 level test work? Doctors usually use a blood test to check vitamin B-12 status, but home urine tests are also available. A doctor can check vitamin B-12 as part of a standard blood test.

What is the condition that results from B12 deficiency anemia?

• Either a lack of vitamin B-12 or a lack of folate causes a type of anemia called megaloblastic anemia (pernicious anemia). With these types of anemia, the red blood cells don’t develop normally.

How do you test for B12 deficiency?

Your doctor will do a physical exam and might order one or more of these tests: