Bowel preparation before diagnostic tests

Before some diagnostic tests, you will have to clean out your bowel completely. This is called bowel preparation and it helps the doctor see inside the bowel clearly. The process can vary, so ask if there are specific instructions for you. It’s important to follow the instructions so you don’t have to repeat the test. Talk to your doctor if you have any questions about the bowel preparation process or side effects.

Here are some ways you may be asked by your doctor to prepare your bowels before a diagnostic test:

Change diet

For a few days before the diagnostic test, you may be told to avoid high-fibre foods, such as vegetables, fruit, wholegrain pasta, brown rice, bran, cereals, nuts and seeds. Instead, choose low-fibre options, such as white bread, white rice, meat, fish, chicken, cheese, yoghurt, pumpkin and potato.

Drink clear fluids

Your doctor might advise you to consume nothing but clear fluids (e.g. broth, water, black tea and coffee, clear fruit juice without pulp) for 12–24 hours before the test. This will help to prevent dehydration.

Take prescribed laxatives

You will be prescribed a strong laxative to take 12–18 hours before the test. This is taken by mouth in tablet or liquid form over several hours, and will cause you to have several episodes of watery diarrhoea.

Have an enema, if required

One common way to clear the bowel is using an enema. This involves inserting liquid directly into the rectum. The enema solution washes out the lower part of the bowel, and is passed into the toilet along with any faeces. You may be given an enema before a colonoscopy if the laxative hasn’t completely cleaned out the bowel or on its own before a sigmoidoscopy.