What is colonic transit testing?
Colonic transit testing using radiopaque markers is a simple, safe test that helps your health care provider understand how quickly food moves through your large intestine (colon). It is often used to find out why you may be experiencing constipation.
This test helps diagnose slow-transit constipation or other conditions that affect bowel movements. It is usually recommended if you have chronic or refractory constipation that does not improve with standard treatments.
How to prepare for colonic transit testing
There are important steps you must take to safely get ready for your colonic transit testing. These are general instructions. Be sure to follow any instructions given to you by your health care provider.
Your doctor or nurse will review the steps with you and make sure that you know how you need to get ready and what you can expect during and after the test. If you have any questions, be sure to bring them up with the doctor or nurse.
Follow these steps before your test
- Stop using laxatives, enemas, and suppositories at least 5–7 days before the test unless instructed otherwise.
- Do not take medications that speed up bowel movements (motility agents) during the test unless instructed otherwise.
- Continue your usual diet unless your health care provider gives different instructions.
- Tell your health care provider if you are pregnant or think you might be, as X-rays are not safe during pregnancy.
What to expect during colonic transit testing
Your health care provider will tell you more specifically what you can expect during the test. Here’s what will happen:
- Day 1: You will swallow a capsule containing tiny rings (markers) that show up on X-rays.
- Days 4–7: You will return for one or more abdominal X-rays to see how far the markers have moved and how many are left in your colon.
- The test is painless and does not require sedation.
- Call your health care provider’s office if you have any questions during or after your colonic transit test.
What to expect after colonic transit testing
Your health care provider will review the X-rays and explain what they mean. Most people can return to normal activities right after the test.
Understanding your results
Your health care provider will discuss your results and what it means for your treatment plan.
- Normal transit: Most markers pass within 4–5 days.
- Slow transit: Many markers remain scattered in the colon after 5 days.
Kyle Staller, MD, MPH
Director, Gastrointestinal Mobility Laboratory, Massachusetts General Hospital, Boston
Reviewed November 2025