Hyperglycaemia (high blood glucose levels) occurs more frequently during illness. This is because the body’s defence mechanism for fighting illness puts more glucose into the blood and prevents your insulin from working properly. This will often cause symptoms like passing more urine and feeling thirsty.

When you have diabetes and are feeling ill, there are certain steps that you must follow to try to avoid your diabetes getting out of control or needing hospital treatment.

Conditions that may upset your blood glucose levels include: 

  • The common cold or flu
  • Diarrhoea and vomiting
  • Urine or chest infections
  • Leg or foot ulcers

Any infection such as tooth abscesses or boils

Have information to help you manage your diabetes during illness to hand.

Test your blood glucose levels more often, at least four times a day, before meals, or more if necessary.

Remember when you are ill:

  • Drink plenty of sugar-free fluids, at least three to four litres through the day, as illness and high blood glucose levels can cause dehydration.
  • Continue to take your insulin / medication, you may even require more whilst ill.
  • If you cannot tolerate any food, replace meals with carbohydrate containing drinks, e.g. milk, complan, soup etc.
  • If these cannot be tolerated take sugary drinks to replace meals, e.g. Lucozade, normal coke, pure orange juice etc.
  • Contact your family doctor (GP) if you are vomiting for more than a few hours.
  • Contact a health professional if you are unsure about what to do if you are unwell.
  • Check your urine for ketones if your blood glucose level is above 15mmol/l.
  • Discuss any over the counter medicines with your local pharmacist. 

See your GP if an infection is suspected.

If you take insulin and your blood glucose levels are over 15mmol/l or you are vomiting test your urine for ketones. The presence of both high blood glucose levels and ketones in the urine indicates a lack of insulin in your body. This can be very serious and you need to seek advice if this occurs.

If you take insulin you should always have ketone strips at home. Check regularly to ensure they are not out of date (see 'What are Ketones?' Patient Information Leaflet).

Never stop your insulin or diabetes tablets when you are ill. Your blood glucose level can rise when you are ill, even if you are not eating. Generally you will need to increase your insulin or diabetes tablets when you are unwell. Speak to your GP, practice nurse or diabetes specialist nurse about dose adjustments.

•    If you experience low blood glucose levels during illness contact your GP, diabetes team or NHS direct for advice on reducing your insulin or diabetes medication.

  • Generally if you take insulin you can follow the guidelines below:
  • If your blood glucose level is below 13mmol/l take your usual insulin.
  • If your blood glucose level is between 13 –20mmol/l take an extra two to four units of quick acting insulin (or your normal insulin if that is all you have).
  • If your blood glucose level is over 20, take an extra four to six units of quick acting insulin (or your normal insulin if that is all you have).
  • You can have this extra dose of insulin every four to six hours if needed. 
  • If your blood glucose level does not improve contact your GP, practice nurse, diabetes specialist nurse or NHS 111 for advice.
  • If you have ketones contact your GP, out of hours doctor, or diabetes team for advice. 

Reduce back to normal dose when better.

Although these steps should help in keeping your diabetes under control whilst you are unwell, there may be a time when you need to attend hospital and be cared for there during your illness.


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Further information


NHS 111
Tel: 111

The North West Diabetes UK 

First floor 
The Boultings
Winwick Street

Tel: 01925 653 281
Email North West Diabetes UK

Diabetes UK

10 Parkway