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Diabetes and illness

If you have diabetes - or have to care for someone who has - it's important to be prepared to cope with illness. Don't delay in contacting your doctor or nurse if you need advice or support.

It is very important to know how to cope with illness if you have diabetes or know or care for somebody with diabetes. If in doubt, always seek advice from your doctor or nurse straightaway.

Any illness or other type of stress will raise your blood sugar (glucose) levels, even if you are off your food or eating less than usual. People with diabetes are unable to produce more insulin to control the glucose level. The increased glucose level can make you become very lacking in fluid in the body (dehydrated).

Acting quickly and following advice helps to keep your glucose levels in the normal range or only slightly high. Because it can sometimes be very difficult to control your blood glucose levels, treatment in hospital may be needed. Hospital treatment may also be needed if you become very dehydrated.

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What happens to my diabetes when I am unwell?

When a person with diabetes is unwell the sugar level in the blood tends to increase. This can happen even with a very mild illness such as the common cold. The blood sugar (glucose) may go up even if you are not eating properly or are being sick (vomiting) or have loose or watery poo (diarrhoea). The increase in blood sugar may make you very lacking in fluid in the body (dehydrated).

What should you do when you are unwell?

  • Contact your GP or practice nurse for advice if you are not sure. You may also need treatment for the illness that is making you feel unwell.

  • If you check your blood sugar (glucose) levels then these checks should be more regular. A practice nurse or district nurse can help with checking blood glucose levels, especially if you don't usually check them regularly.

  • Continue eating as normally as possible. If you don't feel like eating, replace your solid food with soup, milk, ice cream, fruit juice, sugar or honey.

  • It is very important to drink as much sugar-free liquid as possible. This will help you to feel better and help to keep control of your diabetes. Aim to have a glass of water every hour and three litres in 24 hours.

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When should I contact a doctor or nurse for advice?

You should seek medical advice if:

  • You live alone and have no support.

  • You are unable to eat or drink.

  • You are being sick (vomiting) or have loose or watery poo (diarrhoea).

  • Your blood sugar (glucose) level is higher than 25 mmol/L.

  • Your blood glucose level is very low.

  • You have large amounts of ketones or persistent ketones in the urine. Ketones are made when you break down fat in your body.

  • You become drowsy or confused (make sure carers, friends, neighbours and relatives are aware of this).

  • You have any other concerns or feel unsure about what you should do.

What if I take tablets to control my diabetes?

  • You should TAKE YOUR TABLETS AS USUAL but make sure you keep up with food and fluids.

  • If you usually check your blood sugar (glucose) levels at home then check the levels more often. Contact your GP straightaway if your glucose levels stay high (for example, above 13 mmol/L).

  • If you don't usually check your glucose at home and you feel unwell, contact your GP or practice nurse for advice. A practice nurse or district nurse will be able to check your blood glucose level.

  • If you take metformin and you become very lacking in fluid in the body (dehydrated), you should stop taking metformin and contact your GP for advice.

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What if I use insulin to control my diabetes?

  • INSULIN SHOULD NEVER BE STOPPED. Your blood sugar (glucose) may go up when you are unwell, even if you are not eating much.

  • You must check your blood glucose levels more regularly. You should check your blood glucose every four hours or even more often, including through the night. Your dose of insulin may need to be increased or reduced depending on your blood glucose levels. If you are not sure then contact your GP or diabetes specialist nurse for advice.

  • You should also check your urine for ketones at least once or twice each day. Ketones are made when you break down fat in your body. Ketones may appear in the blood and urine due to starvation or because of a lack of insulin. The presence of ketones in the urine may be a warning of diabetic ketoacidosis.

  • Diabetic ketoacidosis is a serious complication of diabetes. Large amounts of ketones are released into the blood. The high level of ketones causes blood acidity, which is harmful to the body. Ketoacidosis is a life-threatening emergency which needs to be treated quickly.

  • Your dose of insulin should be put back to your usual dose when you are better and the blood glucose levels return to normal.

What should I do if I need to take steroid tablets?

Steroid tablets (for example, prednisolone) are very important for treating some illnesses, such as severe asthma. Blood sugar (glucose) levels may increase when you are taking steroids, especially steroid tablets or injections.

It is very important not to stop taking the steroids but you should check your blood glucose levels regularly. Always get advice from your GP if you have diabetes and need to take steroid tablets. Your GP may need to increase or change your diabetes medication while you are taking steroids.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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