Gastroscopy / Flexible Sigmoidoscopy Preparation for People with Diabetes Controlled with Insulin (or Insulin and Tablets)
Please bring all your diabetic medications into hospital with you and your blood glucose testing kit (if you have one).
If you are driving, wait until your blood glucose level is above 5mmol/L.
Please follow instructions in the table overleaf marked ‘What to do with your medication before procedure’.
Preparing for appointments
- Do not drink fluids for 4 hours before the procedure
- Do not eat food for 6 hours before the procedure
- When you travel to and from hospital for your procedure, carry some glucose tablets or a sugary drink.
If you have any symptoms of low blood sugar such as sweating, dizziness, blurred vision or shaking, please test your blood sugar. If it is less than 4mmol/L, take 4 or 5 glucose tablets or 150ml of apple juice or non-diet lemonade or 100ml sugary drink (e.g. Lucozade® Energy Original). Please tell staff at the hospital that you have done this as it is possible that your procedure, for your safety, may have to be postponed.
After the procedure
After the procedure your blood glucose will be checked. When you have recovered, you will be offered food and drink. If you are eating and drinking normally later that day, restart your normal insulin and/or tablets. Please note, your blood glucose levels may be a little unsettled for a day or so.
If you do not improve quickly or if you have any concerns, please phone your GP practice for advice.
What to do with your medication before the procedure
| Medication | Day before admission | Day of procedure | |
| Morning appointment | Afternoon appointment | ||
| Once daily (evening) Lantus®/Glargine or Toujeo® Semglee® or Abasaglar® Tresiba®/Degludec or Insulatard®or Humulin I® | Take as normal | Take as normal | No dose adjustment needed |
| Once daily (morning ) Lantus®/Glargine or Toujeo Semglee® or Abasaglar® Tresiba®/Degludec or Insulatard®or Humulin I® | Take as normal | Take as normal | No dose adjustment needed |
| Twice daily Novomix 30®, Humulin M3® | Take as normal | Take half your usual dose. Your blood glucose will be checked on admission. Resume your normal insulin with your evening meal | Take half your usual dose. Your blood glucose will be checked on admission. Resume your normal insulin with your evening meal |
| Basal Bolus (a long-acting insulin in addition to a pre meal short acting insulin) Novorapid® or Fiasp ® Humalog® or Lyumjev® Apidra® | Take as normal | No breakfast so omit short acting insulin dose Resume your normal insulin when you start eating again Continue to take long-acting insulin | Take your breakfast insulin dose if eating. If your breakfast is less than normal you may need to reduce your dose Omit your lunchtime dose if you are not eating. Your blood glucose will be checked on admission. Resume your normal insulin when you start eating again |
You should resume taking your normal insulin the morning after the procedure. However, your blood glucose may be higher than usual for a day or so.
About this leaflet
Authors: Dinsdale Marjoram
Written: January 2026
Approved: March 2026
Review date: January 2029
Edition: v1