What Is a Schilling Test?

Medically Reviewed by Murtaza Cassoobhoy, MD on May 28, 2023
Written by WebMD Editorial Contributor
4 min read

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.

Vitamin B12 is a vital nutrient for humans. It is not produced naturally in the body. Vitamin B12 produces red blood cells, keeps our nerves functioning properly, and even aids in DNA synthesis.

Most adults get plenty of vitamin B12 from food sources. Some people have trouble absorbing it. Vitamin B12 deficiency only affects between 1.5% and 15% of the public.

For example, people over 50 may not have enough hydrochloric acid in their stomach to absorb vitamin B12 from food. But they may be able to absorb it from fortified foods or dietary supplements. Side effects of Vitamin B12 deficiency include:

  • Anemia
  • Weakness and fatigue
  • Sore mouth and tongue
  • Constipation
  • Decreased appetite and weight loss
  • Tingling and numbness in the hands and feet
  • Dizziness and lightheadedness
  • Poor memory and confusion

Dr. Robert F. Schilling worked on urine radioactivity testing for vitamin B12 absorption for much of his career. The Schilling test was named after him. 

Dr. Schilling studied medicine at the University of Wisconsin-Madison. He completed his postdoctoral training at Philadelphia General Hospital, the Boston City Hospital, and the University of Wisconsin Hospital in Madison.

The Schilling test was divided into two stages.

Stage One. In the first stage of the Schilling test, a person swallowed radiolabeled vitamin B12A (vitamin B12 joined with a radioactive substance). An hour later, they would receive an injection of unlabeled vitamin B12. This ensured that the radioactive B12 did not bind to any vitamin-B12-depleted tissue in the body.

After the administration of the B12, the patient’s urine was collected and monitored for 24 hours. This was to assess the absorption and excretion of vitamin B12. A healthy person would be able to absorb the radioactive B12A administered during Stage One.

If the patient excreted 8% to 40% of the radioactive vitamin B12 through their urine within 24 hours, it was considered a “normal” or healthy result. If Stage One showed abnormal results, Stage Two was performed 3 to 7 days later.

Stage Two. If Stage One yielded abnormal results, Stage Two was next. It examined whether there was a deficiency of intrinsic factors, which are proteins that help your intestine absorb B12. In Stage Two, the Stage One procedure was repeated with the addition of an oral dose of an intrinsic factor. If the result was still abnormal, this typically indicated pernicious anemia.

Pernicious anemia is one of several types of anemia. This is a condition that causes a person’s blood to have a lower number of red blood cells than healthy people. When someone has pernicious anemia, the body doesn’t make sufficient, healthy red blood cells. It stems from a vitamin B12 deficiency.

Pernicious anemia puts people at an increased risk for weakened bone strength and stomach cancer. It may also cause other symptoms or health problems, such as:

  • Nerve damage
  • Neurological problem
  • Digestive problems‌

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. If you have anemia, it will be clear that you have fewer red blood cells than a healthy person. If your anemia is caused by a lack of vitamin B12 and/or vitamin B9, your red blood cells will appear large and weak.

If your blood test(s) show you have a vitamin B12 deficiency, you may need additional tests. These could include an antibodies test or a methylmalonic acid test.

B12-fortified foods can help to fulfill your vitamin B12 quota. This is especially true if you’re a vegan, vegetarian, or simply do not eat animal products frequently.

The best sources of vitamin B12 include:

  • Cereals, nutritional yeast, and other foods fortified with vitamin B12
  • Dairy products, like milk and yogurt
  • Eggs
  • Beef liver
  • Clams
  • Most poultry, meat, and fish

If you are unable or unwilling to get vitamin B12 from food sources, you can take a supplement. Vitamin B12 supplements come in capsules, tablets, nasal gels, and even injections. Studies have not shown a notable difference in absorption rates between these different kinds of vitamin B12 supplements.