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HealthInfo Canterbury

Colonoscopy & sigmoidoscopy if you have diabetes

This information is to help you manage your diabetes before your procedure. Read it with the booklet about preparing your bowel for your colonoscopy or sigmoidoscopy that you have received from the Gastroenterology Department.

FDP blood sugarMost people can manage their diabetes by following this advice. But if you've recently been admitted to hospital because of poorly controlled diabetes, or if you're having major problems with low blood sugar (hypoglycaemia), make sure you talk to your GP or diabetes nurse. Some people may need to go to hospital to prepare for their colonoscopy or sigmoidoscopy.

Managing your diabetes will probably be easier if you have a morning appointment. If you don't have a morning appointment, please phone the number on your booking letter to see if your procedure can be rescheduled to an earlier time.

Carefully read the information about food and clear fluids on page 2 of the booklet you've been given on bowel preparation.

Don't worry if your blood glucose level isn't as well controlled as usual, as long as it's above 4mmol/L but below 15mmol/L.

Bring your blood glucose monitor, insulin and injecting equipment with you to the appointment. Also bring some dextrose tablets or whatever you would normally use to manage a hypo.

How to prepare

If you take tablets for diabetes

If you are using insulin

Depending on how much carbohydrate you manage to take when you're just on fluids and what your blood glucose levels are, you'll need less insulin than usual. It's important to monitor your blood glucose levels at least four times a day and more often if you have any symptoms of hypoglycaemia. See the information below on what clear fluids you can use to raise your glucose level if it is too low.

If you are having an injection of long-acting insulin in the morning (Humulin NPH, Lantus, Protaphane)

If you are taking an injection of long-acting insulin in the evening (Humulin NPH, Lantus, Protaphane)

If you are on one or more injections of short-acting insulin (Actrapid, Apidra, Humalog, Humulin R, NovoRapid)

The amount of short-acting insulin you'll need depends on how much carbohydrate you get from the clear fluids.

If you are taking two injections a day of pre-mixed insulin (Humulin mixture 30/70, Mixtard 30, Penmix 30, Penmix 40, Penmix 50, Humalog Mix 25, Humalog Mix 50, NovoMix 30).

If you are taking tablets and insulin

Carbohydrates in clear fluids

FDP bubbles in glassThese clear fluids have a similar amount of carbohydrate to one medium slice of bread (15 g of carbohydrate):

You will digest carbohydrates in clear fluids more quickly than other carbohydrates so you should spread the fluids through the day. Have some at lunchtime, some mid-afternoon, some at dinnertime, some after dinner and some at midnight, depending on your blood glucose readings. You can also have some of these carbohydrate-containing fluids up until four hours before your procedure. If you need any after that time because your blood sugar is low, let the staff know when you arrive for your procedure.

Written by Endocrinology and Diabetes Services, Christchurch Hospital. Adapted by HealthInfo clinical advisers. Last reviewed July 2019.

See also:

Managing insulin when you are sick

Page reference: 96281

Review key: HIDIE-96281