Schilling Test - Procedure, Indication, and Complication

Introduction:

Schilling test is an investigation test specially done by analyzing the level of vitamin B12 expelled in the urine by using radioactive cobalt. The name Schilling test received its name after Dr.Robert F. Schilling, who invented it. This test uses radioactive cobalt, which is ingested into the system, and the ratio between the output of the vitamin B12 absorbed by the body and the amount expelled in urine. It is used in cases suspected of vitamin B12 deficiency in the bloodstream, also known as megaloblastic anemia. The Schilling test is also known as vitamin B12 absorption test.

What Is Vitamin B12 Deficiency?

Vitamin B12 is one of the water-soluble vitamins that are available in the natural sources required for the function of the body. Vitamin B12 consists of minerals called cobalmines, which are the cobalt compounds. These cobalmines are scientifically called 5- 5-deoxy adenosylcobalamin and methylcobalamin, active metabolites (the active components of vitamin B12). Vitamin B12, as an enzyme, is a necessary agent for the development, growth, and myelination and is mainly involved in the greater and effective functioning of the red blood cells, DNA synthesis, and the central nervous system.

This vitamin B12 also serves as a precursor for two enzymes, namely the L- methylmalonyl-coA mutate and methionine synthetase, which converts homocysteine to an essential amino acid called methionine. Vitamin B12 is found mainly in meat, eggs, fish, poultry, dairy products such as cheese, milk, etc, and vegetarian sources in tofu, tempeh, edible seaweed, yeast, etc., Although most adults have a high intake of vitamin B12, most of the time, there is a defect in absorption involving around 1.5 to 15 percent of the population. The deficiency of vitamin B12 leads to systemic conditions like:

• Fatigue.

• Systemic weakness.

• Mouth and tongue ulcers.

• Constipation.

• Anemia.

• Loss of appetite.

• Weight loss.

• Numbness or tingling sensation in the foot and hands.

How Is Schilling Test Done?

The Schilling test can be done in two main stages,

• Stage 1: In stage 1, the patient is asked to orally consume radioactive vitamin B12, following it with an intramuscular injection of vitamin B12 after an hour. This is because the injection ensures the radioactive substance gets bound to the depleted or broken-down vitamin B12. This is allowed in circulation for around twenty-four hours, after which the urine sample is collected and monitored. If this stage shows abnormal results, another analysis can be done as stage 2 after three to seven days.

• Stage 2: This stage is done or preferred when the stage 1 results are wavering. This is done by similarly repeating the test and collecting the urine sample after twenty-four hours.

Although these tests provide the outcome, sometimes the outcome can be negative again, and that is because of a bacterial infection or an overgrowth. In this case, stage 3 testing is done. In this scenario, the testing is done following two weeks of antibiotics and filled by administering vitamin B12. If the stage 3 test comes out as normal again, then stage 4 is preferred to detect pancreatic disorders.

When Is the Schilling Test Indicated?

Shillings test is preferred in patients showing symptoms of cobalamin deficiency as it helps interpret vitamin B12 levels. The stage 3 shilling test also helps establish bacterial infection, and stage 4 helps indicate pancreatic diseases. Vitamin B12 deficiency also includes conditions like macrocytic anemia, neurological abnormalities that cause alterations in walking patterns, and folic acid deficiency cases.

What Are the Clinical Interpretations of the Schilling Test?

If the patient has no discrepancy, the net result will show a normal outcome in the urine output. Still, if there is a defect in the ileum or lack of any intrinsic factor from the systemic circulation, it shows an abnormal outcome. When there is an excretion of around ten to forty percent of the radioactive B12 after 24 hours of monitoring, then it is considered normal.

How Is the Schilling Test Clinically Significant?

As discussed earlier, the Schilling test is used mainly in cases of anemia like megaloblastic anemias, where there is a drastic difference in the rate of vitamin b12 or cyanocobalamin. This test is indicated to determine the levels in the blood.

• To Indicate the Presence of Cobalamin Deficiency- Cobaline is the chemical name of vitamin B12, which is required for the development and functioning of the DNA (deoxyribonucleic acid).

• To Know the Vitamin B12 Absorption Status -The significance of knowing the rate of absorption status of this vitamin is because, most of the time, even though the vitamin is consumed through food, not all the time, it is metabolized into the appropriate levels to benefit the body.

• To Ensure Folic Acid Levels - Folate is a water-soluble form of vitamin B9 that occurs naturally in various food sources. Folate plays a role in forming DNA (deoxyribonucleic acid), RNA (ribonucleic acid), and protein metabolism. It is essential for the breakdown of homocysteine, an amino acid that may be detrimental to the body if present in large quantities. Folate is also required to generate healthy red blood cells and is especially important during fast growth, such as pregnancy and fetal development.

• To Detect an Infection or Defect in the Terminal Ileum: When B12 cannot be absorbed for an extended length of time due to nutritional insufficiency, malabsorption, or a lack of intrinsic factor, hepatic reserves are depleted, resulting in a deficiency. Intrinsic factor is a glycoprotein generated by stomach parietal cells required for vitamin B12 absorption in the terminal ileum. It is essential to look for an infection or an abnormality in the terminal ileum.

What Are the Contraindications and Complications of the Schilling Test?

Although the test is very useful and easy to perform, some factors will affect the performance of the test or trouble the patients, and they are:

• Diarrhea.

• Vomiting.

• Nausea.

• Fall in vitamin B12 levels.

Sometimes, it may contradict people with allergies, so caution is important.

Conclusion:

The Schilling test was one of the basic tests developed to find the presence of vitamin B12 deficiency in the system. Although this testing system is easier to perform, the repetitive process by which the procedure is done can be tiresome for certain patients. However, knowing the levels of vitamin B12 and folic acid is essential for the body's functioning, as the Schilling test enables us to keep those levels and maintain them periodically.