What is a Schilling test?

The Schilling test is a medical procedure used to determine whether you’re absorbing vitamin B-12 properly. Your doctor may choose to order this test if you have a vitamin B-12 deficiency or pernicious anemia. The Schilling test usually involves up to four stages. It also involves analyzing your urine samples to help determine the cause of the vitamin deficiency.

Your body uses vitamin B-12 to make red blood cells. Anemia is a condition in which your body doesn’t have enough healthy red blood cells to transport oxygen to your organs and tissues. The test is designed to measure how well your body absorbs vitamin B-12 from your digestive tract.

Why the Schilling test is performed

Your doctor may recommend the Schilling test if you have a vitamin B-12 deficiency. The test can help them determine whether your stomach is producing “intrinsic factor.” The intrinsic factor is a type of protein required for vitamin B-12 absorption. Without it, your body will be unable to absorb vitamin B-12, resulting in pernicious anemia.

How to prepare for the Schilling test

You can’t receive any intramuscular injections of vitamin B-12 three days before your test. Though you may drink water, you’ll need to avoid food for eight hours before the test. You can then eat normally after the test.

How the Schilling test is administered

The Schilling test has four stages. After you’ve taken enough supplements to restore a healthy level of vitamin B-12 in your system, your doctor may advise you to undergo the test. This takes several weeks.

Stage 1

In stage 1, the doctor will give you two doses of a vitamin B-12 supplement. The first dose will be in liquid form, which will contain a “radiolabeled” dye that can be detected in your urine. Radiolabeling involves using a harmless radioactive element to track a compound through your body. In this case, your doctor tracks the dose of vitamin B-12. They can track where it goes and how fast it gets absorbed into the body.

The second dose of vitamin B-12 is given as an injection one hour later. These supplements alone aren’t enough to return your body’s vitamin B-12 to a healthy level. However, they can be used to test your body’s ability to absorb the vitamin.

Over the next 24 hours, you’ll need to collect a urine sample. You must then bring it to your doctor’s office so your rate of vitamin B-12 absorption can be tested. If stage 1 results are abnormal, your doctor will perform stage 2 within three to seven days.

Stage 2

In this stage, your doctor will give you another oral sample of radiolabeled vitamin B-12, along with intrinsic factor. This test will show whether a lack of intrinsic factor is the reason for your low levels of vitamin B-12.

You’ll collect a urine sample over the next 24 hours and deliver it to your doctor to be analyzed. If the results of this test are normal, it means you lack intrinsic factor and you most likely have pernicious anemia. If the results are abnormal, your doctor will perform stage 3.

Stage 3

This test is done to see if an abnormal growth of bacteria is causing your low vitamin B-12 levels. Before administering another dose of radiolabeled vitamin B-12, your doctor will prescribe a two-week course of antibiotics. If the results of this test are abnormal, they’ll perform stage 4.

Stage 4

This test will show your doctor if problems with your pancreas are causing low levels of vitamin B-12. In this stage, your doctor will give you a three-day course of pancreatic enzymes followed by a radiolabeled dose of vitamin B-12. You’ll collect a urine sample over the following 24 hours.

How to collect a 24-hour urine sample

For adults

On day 1, urinate into the toilet after waking up. Collect all of your urine in a clean container for the next 24 hours.

On day 2, Urinate into the same container after getting up. Seal the container and label it with your name and the date. Keep it refrigerated until you can return it to your doctor.

For infants

If you need to collect a 24-hour urine sample from your baby, follow these steps:

1. Wash the area around your baby’s genitals.
2. Place the urine collection bag on your baby, and secure the adhesive tape.
3. Place a diaper on your baby, covering the collection bag.
4. Check your baby regularly and change the bag each time it has urine in it.
5. Drain the urine into a clean container
6. Deliver the container to your doctor as soon as you’ve collected the required amount of urine.

What to expect after the Schilling test

If you have a vitamin B-12 deficiency, your doctor may perform further tests to determine whether it’s related to any of the following factors:

• atrophic gastritis with reduced stomach acid production
• Celiac disease
• Crohn’s disease
• Graves’ disease
• bacterial overgrowth
• pancreatic insufficiency
• alcoholism
• certain prescribed medications

Understanding the results

You have a normal test result if you urinate 8 to 40 percent of the radiolabeled vitamin B-12 within 24 hours.

Abnormal Results

Abnormal stage 1 and normal stage 2 results indicate that your stomach is unable to make intrinsic factor.

Abnormal stage 1 and 2 results may indicate:

• pernicious anemia
• celiac disease
• liver disease
• biliary disease
• hypothyroidism

Abnormal stage 3 results indicate that abnormal bacterial growth is causing your low levels of vitamin B-12.

Abnormal stage 4 results indicate that problems with your pancreas are causing your low levels of vitamin B-12.

Risks of the Schilling test

In some cases, the Schilling test may produce the following minor side effects:

• soreness at the site of the vitamin injection
• redness at the site of the vitamin injection
• mild nausea
• lightheadedness

A false-positive result occurs when the test indicates you have a condition that you don’t have. The Schilling test may sometimes give a false-positive result. A poor urine collection is usually the cause of this. However, it may also happen due to kidney disease or problems with the lining of your small intestine. You may have to take the test again if your doctor suspects you have a false-positive result.

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