A bowel transit time test measures how long it takes for food to travel through the digestive tract. After you chew and swallow your food, it moves into your stomach, where it is mixed with acid and digestive enzymes. After your food leaves your stomach, it is squeezed through your small intestine, where nutrients are absorbed for use by your body. The food then goes into your large intestine (colon) where water is absorbed. Whatever hasn't been digested and absorbed by your intestines combines with bacteria and other waste products and becomes stool (feces). Stool is expelled from your body through your anus. The time it takes for food to travel from your mouth through your digestive tract to your anus is your bowel transit time. Sometimes, just the time it takes for food to travel through the colon is measured. This is called the colonic transit time.
Bowel transit time depends on what types of food you eat and how much you drink. For example, people who eat lots of fruits, vegetables, and whole grains tend to have shorter transit times than people who eat mostly sugars and starches. Because different people have different transit times, experts disagree about how useful this test is. Some doctors do not recommend bowel transit time testing.
For this test, you swallow one or more gel capsules filled with markers that will show up on an X-ray. The markers look like white spots or rings in the X-ray pictures. When you will have X-rays depends on the type of test done. Most commonly, you will have an X-ray test 5 days after swallowing the markers. This will show how the markers have moved through your intestines. Or you may swallow multiple capsules full of markers on three days in a row. In this case, you will have X-ray tests on multiple days to check the progress of the markers through your intestines.
Why It Is Done
Bowel transit time tests may be done to:
- Find the cause of constipation or the slow movement of food through the digestive tract.
- See if one place in your intestines is slowing down movement more than the rest of your intestines.
Bowel transit time tests are not done to find the cause of diarrhea.
How To Prepare
Tell your doctor if you are or might be pregnant before having this test.
You may need to change your diet for a few days before having this test. You may also need to stop taking medicines for a short time before having a bowel transit time test. Tell your doctor about all the prescription and nonprescription medicines you are taking.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form ( What is a PDF document? ).
How It Is Done
Your doctor will give you one or more gel capsules filled with markers that will show up on an X-ray. Follow your doctor's instructions about when to take the capsules. You may take only one capsule. Or you may be told to take one at a certain time for 2 or 3 days in a row. You will then have X-rays taken of your belly. These are usually done on day 5. The percentage of markers that show up on the X-ray tells your doctor if you have a normal bowel transit time.
How It Feels
Bowel transit time tests do not cause pain.
You will not feel discomfort from the X-rays used for the test. The X-ray table may feel hard and the room may be cool. You may find that the positions you need to hold are uncomfortable.
This test is not recommended if you are pregnant because the radiation from the X-ray can harm your developing baby (fetus).
A bowel transit time test measures how long it takes for food to travel through the digestive tract.
Bowel transit time depends on what types of food you eat and how much you drink. Different people have different bowel transit times.
Fewer than 20% of the markers show up on an X-ray after 5 days (120 hours).
More than 20% of the markers show up on an X-ray after 5 days (120 hours).
What Affects the Test
You may have an abnormal bowel transit time if you:
- Have an infection in your intestines.
- Do not drink enough fluids (dehydration).
- Have a disease, such as a narrowing (stricture) in your intestine, an underactive thyroid gland (hypothyroidism), diabetes, or Hirschsprung's disease.
- Are eating less than you usually do or you are eating different kinds of food than usual.
- Take medicines, such as cold medicines, iron, or medicine used to control blood pressure and pain.
What To Think About
- Bowel transit time also can be done using a dye capsule. You swallow a capsule containing a bright red dye and measure the amount of time until you see the red color appear in your stool. You may also measure the time needed for all of the dye to pass through your colon.
- Many doctors do not think that bowel transit time testing is useful. Different people have different bowel transit times on different days.
- This test is not recommended if you are or might be pregnant.
- You can usually speed up bowel transit time if you increase the amount of fruits, vegetables, and whole grains that you eat each day. To learn more, see the topic Healthy Eating.
- It is possible to have a daily bowel movement but still have a slow bowel transit time.
- Lembo A, Camilleri M (2003). Chronic constipation. New England Journal of Medicine, 349(14): 1360–1368.
Other Works Consulted
- Lembo AJ, Ullman SP (2010). Constipation. In M Feldman et al., eds., Sleisenger and Fordtran's Gastrointestinal and Liver Disease, 9th ed., vol. 1, pp. 259–284. Philadelphia: Saunders.
Current as of: March 28, 2019
Author: Healthwise Staff
Adam Husney MD - Family Medicine
Martin J. Gabica MD - Family Medicine
Jerome B. Simon MD, FRCPC, FACP - Gastroenterology
Current as of: March 28, 2019