Preparation with Gastrografin
CT enema scan - Overview
Important – only follow these instructions if:
- you do not have an iodine allergy and can have full bowel preparation
You have been asked to take a liquid dye called Gastrografin®, that ‘tags’ poo that is left in your bowel so that it can be seen on the CT scan. This is called ‘faecal tagging’. Gastrografin is also a laxative that helps to empty your bowel before the CT scan.
Before the CT enema scan
You should have received a bottle of liquid Gastrografin. You need to take this in 2 separate doses (amounts). You can mix this with water or juice if you prefer.
Only a tiny amount of the liquid is absorbed by your body. The rest gets mixed with the poo in your large bowel, and will eventually be passed out of your body in your poo. It might make your stool look white. The liquid shows up in your bowel on the CT, and helps the doctor to read the scan.
Gastrografin is an extremely effective laxative and can work quite quickly. We recommend you stay close to the toilet after taking it. As well as the diet instructions, it’s important to drink plenty of water to avoid becoming dehydrated. The recommended timing of the doses of Gastrografin mean that the effects will have worn off by the time you need to come to the hospital.
If you have any questions about the instructions, or have not received your bowel preparation, please contact the CT department. Please take your regular medicines as normal, unless you are told otherwise.
Do not take Gastrografin if you have an untreated thyroid disease, or an allergy to iodine, or an uncorrected thyroid disease.
Patients with diabetes or restricted diets for religious or ethical reasons should contact the CT department for dietary advice as soon as you receive your appointment.
7 days before your scan
You need to follow these instructions from 7 days before your scan date.
What you need to avoid
- Do not have any fibre.
- Do not have any iron tablets (check your medicine bottles for iron, ferrous, ferric, feredetate)
2 days before your scan
You should only have small meals. For snacks you can have rich tea or other plain biscuits.
What you need to avoid
- Do not have any fruit or vegetables
- Do not have any seeds, oats or wholemeal
- Do not have any milk
- Do not have any alcohol
Here is a list of the foods you should eat, and the medicines you need to take 2 days before your scan.
- Tea or coffee (with no milk)
- White bread
- Seedless jam, marmite or marmalade
- Rice Krispies® or cornflakes
- Boiled or poached eggs
- Clear soup or broth
- 2 egg-sized skinless boiled potatoes
- 2 slices of white bread
- Tablespoon of plain white pasta, noodles or boiled rice, soya and tofu
- White fish, meat or fish for example, well cooked, tender, lean beef, lamb, ham veal, pork, poultry, fish and shellfish
- Lean skinless chicken
- Black tea or coffee
- Take 50mls of Gastrografin mixed with 50mls of water or squash
- Clear soup or broth, 2 egg sized skinless boiled potatoes, 2 slices of white bread, tablespoon of plain white pasta, noodles, boiled rice, soya or tofu.
- Meat (for example, well-cooked, tender, lean beef, lamb, ham veal, pork, poultry_ or white fish or shellfish, lean skinless chicken
- Black tea or coffee
1 day before your scan
What you need to avoid
- Do not have any cereals
- Do not have any milk or cream
Here is a list of the foods you should eat, and the medicines you need to take 2 days before your scan.
- White bread
- Seedless jams, marmalade, or marmite
- Black tea or coffee
- Strained clear soup/broth
- 2 or 3 crackers or water biscuits
- 1 serving of plain jelly
- Black tea or coffee
- Snacks of 2 or 3 rich tea or plain biscuits
- Take 50mls of Gastrografin mixed with 50mls of water or squash.
- Strained clear soup/broth
- 2 or 3 crackers or water biscuits
- 1 serving of plain jelly
- Black tea or coffee
- Do not have any more food until after the procedure
- Do not have any alcohol
You can drink as much (non-fizzy) water, clear soft drinks, black coffee and black tea as you like.
The day of your scan
You must not have any food before your scan.
You can drink as much (non-fizzy) water and clear soft drinks as you want.
You can suck a few boiled sweets.
Having a CT scan
Read about what happens during and after having your CT scan.
Resource number 3048/VER5
Publish date: March 2026
Review date: March 2029
