Please read this information and follow the instructions carefully before your CT colonography scan. The test depends on your large bowel being as empty as possible by taking the ‘Gastrografin®’ liquid that our pharmacy will send out to you in a separate envelope in the post. Otherwise the test may have to be repeated.
If you are unable to complete the preparation or follow the instructions, please contact the Imaging Department before attending your appointment on 07929 875241.
In the separate pack from the pharmacy you will find:
- Two 100ml bottles of Gastrografin®
- One measuring cup
Gastrografin® is essential to prepare your bowel for the test. It contains iodine and tastes quite strong. It can have a laxative effect (may cause diarrhoea).
If you have been told that you are allergic to X-ray dye (contrast), which contains iodine, then call us before going any further 07929 875241.
Stop any iron tablets, but continue to take all other medications and laxatives you usually take.
Eat only low fibre foods, which includes the following:
- Milk (2 cups per day), plain yoghurt, cheese, butter,
margarine.
- White fish or chicken (boiled, steamed or grilled).
- Eggs, tofu, white pasta, white rice, white bread.
- Potatoes with no skin (e.g. mashed, boiled).
- Clear soups (no solid bits e.g. sieved chicken noodle), Bovril, Oxo.
- Clear jelly, boiled sweets, ice cream, chocolate (no fruit or nut pieces).
- Salt, pepper, sugar, sweeteners and honey.
Have plenty to drink throughout the day:
- Water, tea, coffee, squash, fizzy drinks, clear fruit juices (e.g. apple/ cranberry).
Do not eat high fibre foods, such as:
- Red meat, pink fish (e.g. salmon)
- Fruit, vegetables, salad, mushrooms, sweetcorn.
- Cereals, nuts, seeds, pips, bran, beans, lentils.
- Brown bread, brown or wild rice, brown pasta.
- Pickles, chutneys.
Eat a low fibre diet throughout all of today
At Breakfast:
- Eat only low fibre foods (see list above)
- Drink 20mls of the First bottle of Gastrografin® using the measuring cup provided
- DO NOT MIX IT WITH WATER
Diabetic patients only: Take insulin/ diabetic tablets with your breakfast
At Lunch:
- Eat only low fibre foods (see list above)
- Drink 20mls of the First bottle of Gastrografin® using the measuring cup provided
- DO NOT MIX IT WITH WATER
At Dinner:
- Eat only low fibre foods (see list above)
- Drink 20mls of the First bottle of Gastrografin® using the measuring cup provided
- DO NOT MIX IT WITH WATER
Diabetic patients only:
- Check blood sugar four times during the day
- If at any point your blood sugar is below 5, drink clear sugary liquids to avoid a ‘hypo’.
Continue the low fibre diet throughout all of today.
At Breakfast:
- Eat only low fibre foods (see list in Two days before your test, above)
- Drink 20mls of the First bottle of Gastrografin® using the measuring cup provided
- DO NOT MIX IT WITH WATER
Diabetic patients only:
- Take insulin/ diabetic tablets with your breakfast
At Lunch:
- Eat only low fibre foods (see list in Two days before your test, above)
- Drink 20mls of the First bottle of Gastrografin® using the measuring cup provided
- DO NOT MIX IT WITH WATER
At Dinner:
- Eat only low fibre foods (see list in Two days before your test, above)
- Drink 20mls of the Second bottle of Gastrografin® using the measuring cup provided
- DO NOT MIX IT WITH WATER
Diabetic patients only:
- Reduce your insulin dose by half, continue your diabetic tablets as normal.
Do not eat any solid food, you may drink water or sugary drinks. You can eat and drink normally as soon as the test is finished.
At 7am or earlier:
- Drink 40mls of the Second bottle of Gastrografin® using the measuring cup provided
- DO NOT MIX IT WITH WATER
- You will have some Gastrografin® liquid still left in the bottle, please discard this.
Diabetic patients only:
If you have a Morning appointment:
- Continue to drink clear sugary fluids.
- DO NOT take anymore insulin/ diabetes tablets until after the test.
- Check blood sugar if you can before arriving at the hospital.
- Bring insulin/ diabetic tablets and a light meal (e.g. sandwich) with you to the hospital to have after the test.
If you have a Afternoon appointment:
- Continue to drink clear sugary fluids.
- Take half your normal dose of insulin in the morning only.
- Do not take diabetes tablets.
- Check blood sugar if you can in the morning and before arriving at the hospital.
- Bring insulin/ diabetic tablets and a light meal (e.g. sandwich) with you to the hospital to have after the test.
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Page last updated: 04 July 2025
Review due: 01 July 2027