Colonic transit study

A colonic transit study looks at how your large bowel (colon) is working. The test helps to diagnose any conditions.

The large bowel transports food from your small intestine to your bottom (anus). This study checks how quickly food moves through your large bowel.

During a colonic transit study, you have 1 or 2 X-rays of your tummy (abdomen).

Before your X-ray, we send you capsules to swallow. These capsules contain small markers, which show up on X-ray. This helps the radiology doctor (radiologist) to check how your bowel is working.

Preparing for the test

Before your X-ray, we send you 6 capsules to swallow. You need to swallow 2 capsules a day for 3 days. These capsules contain small markers, which show up on X-ray.

If you are vegetarian or vegan, please be aware that the capsules contain gelatine (an animal product).

You can eat and drink normally throughout this study.

Do not use any laxatives (medicine to help you poo) before or during this study.

Taking the capsules

If you are of childbearing age and have regular periods, you need to take the first capsules within the first 7 days of your period.

At the back of the silver packet, you will notice six numbered capsules (1 1, 2 2, 3 3).

Day 1, any Saturday morning Swallow the first pair of capsules (Numbers 1 1) with water at breakfast.
Day 2, Sunday morning Swallow the second pair of capsules (Numbers 2 2) with water at breakfast.
Day 3, Monday morning Swallow the third pair of capsules (Numbers 3 3) with water at breakfast.
Day 6, Thursday

Go to the X-ray Department between 8.30am and 5.30pm for your X-ray. This is on the 1st Floor, Lambeth Wing, St Thomas’ Hospital.

Risks of taking the capsules 

Do not take the capsules if:

  • there is any chance that you could be pregnant. Contact the nurse specialist or X-ray department if you believe you are pregnant. Radiation can be harmful for an unborn baby.
  • you are allergic to gelatine or barium sulphate because the capsules contain them.

Ask for an urgent GP appointment or call the X-ray department if

you have an allergic reaction such as:

  • a rash
  • itchiness
  • redness

Call 999 or go to A&E if

you have an allergic reaction, such as swelling of the:

  • face
  • lips
  • tongue
  • throat

Having an X-ray

The X-ray is a quick and painless test. It only takes a few minutes, but please allow enough time to be in the department for 30 minutes.

We ask you to change into a hospital gown.

The radiographer calls you into the X-ray room and asks you to lie flat on your back on the X-ray table. You are helped into position.

Risks of having an X-ray

All X-rays use a type of radiation called ionising radiation. The amount (dose) used in medical X-rays is low and the risks are small. 

The radiation is similar in strength to other types of natural radiation that people are exposed to everyday without even realising it.

The radiographer doing your X-ray makes sure that your dose is kept as low as possible and that the benefits of having the X-ray outweigh any risk.

After the X-ray

You can continue any laxative medicines that you have stopped for the test.


The doctor or specialist who referred you for the procedure sends you your test results. You need to contact them to arrange a follow-up appointment.

We want to involve you in decisions about your care and treatment. 

The radiographer asks you if you are happy to have the X-ray. This is called verbal consent. It might only involve the radiographer checking that you are booked for the correct X-ray.

If you would like more information about our consent process, please speak to a member of staff caring for you.

Resource number: 4925/VER2
Last reviewed: March 2020
Next review due: March 2023

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