Hyperglycaemia is the medical term for a high blood sugar (glucose) level. It's a common problem for people with diabetes.

It can affect people with type 1 diabetes and type 2 diabetes, as well as pregnant women with gestational diabetes.

It can occasionally affect people who don't have diabetes, but usually only people who are seriously ill, such as those who have recently had a stroke or heart attack, or have a severe infection.

Hyperglycaemia shouldn't be confused with hypoglycaemia, which is when a person's blood sugar level drops too low.

This information focuses on hyperglycaemia in people with diabetes.

Is hyperglycaemia serious?

The aim of diabetes treatment is to keep blood sugar levels as near to normal as possible. But if you have diabetes, no matter how careful you are, you're likely to experience hyperglycaemia at some point.

It's important to be able to recognise and treat hyperglycaemia, as it can lead to serious health problems if left untreated.

Occasional mild episodes aren't usually a cause for concern and can be treated quite easily or may return to normal on their own. However, hyperglycaemia can be potentially dangerous if blood sugar levels become very high or stay high for long periods.

Very high blood sugar levels can cause life-threatening complications, such as:

Regularly having high blood sugar levels for long periods of time (over months or years) can result in permanent damage to parts of the body such as the eyes, nerves, kidneys and blood vessels.

If you experience hyperglycaemia regularly, speak to your doctor or diabetes care team. You may need to change your treatment or lifestyle to keep your blood sugar levels within a healthy range.

Symptoms of hyperglycaemia

Symptoms of hyperglycaemia in people with diabetes tend to develop slowly over a few days or weeks. In some cases, there may be no symptoms until the blood sugar level is very high.

Symptoms of hyperglycaemia include:

Symptoms of hyperglycaemia can also be due to undiagnosed diabetes, so see your GP if this applies to you. You can have a test to check for the condition.

What should my blood sugar level be?

When you're first diagnosed with diabetes, your diabetes care team will usually tell you what your blood sugar level is and what you should aim to get it down to.

You may be advised to use a testing device to monitor your blood sugar level regularly at home, or you may have an appointment with a nurse or doctor every few months to see what your level is.

Target blood sugar levels differ for everyone, but generally speaking:

  • if you monitor yourself at home – a normal target is 4-7mmol/l before eating and under 8.5-9mmol/l two hours after a meal
  • if you're tested every few months – a normal target is below 48mmol/mol (or 6.5% on the older measurement scale)

What causes high blood sugar?

A variety of things can trigger an increase in blood sugar level in people with diabetes, including:

  • stress
  • an illness, such as a cold
  • eating too much, such as snacking between meals
  • a lack of exercise 
  • dehydration
  • missing a dose of your diabetes medication, or taking an incorrect dose
  • over-treating an episode of hypoglycaemia (low blood sugar)
  • taking certain medicines, such as steroid medication

Occasional episodes of hyperglycaemia can also occur in children and young adults during growth spurts.

Treating hyperglycaemia

If you've been diagnosed with diabetes and you have symptoms of hyperglycaemia, follow the advice your care team has given you to reduce your blood sugar level.

If you're not sure what to do, contact your GP or care team.

You may be advised to:

  • change your diet – for example, you may be advised to avoid foods that cause your blood sugar levels to rise, such as cakes or sugary drinks
  • drink plenty of sugar-free fluids – this can help if you're dehydrated
  • exercise more often – gentle, regular exercise such as walking can often lower your blood sugar level, particularly if it helps you lose weight
  • if you use insulin, adjust your dose – your care team can give you specific advice about how to do this

You may also be advised to monitor your blood sugar level more closely, or test your blood or urine for substances called ketones (associated with diabetic ketoacidosis).

Until your blood sugar level is back under control, watch out for additional symptoms that could be a sign of a more serious condition (see below).

When to get urgent medical attention

Contact your diabetes care team immediately if you have a high blood sugar level and experience the following symptoms:

These symptoms could be a sign of diabetic ketoacidosis or a hyperosmolar hyperglycaemic state (see above) and you may need to be looked after in hospital.

How to prevent hyperglycaemia

There are simple ways to reduce your risk of severe or prolonged hyperglycaemia:

  • Be careful what you eat – be particularly aware of how snacking and eating sugary foods or carbohydrates can affect your blood sugar level.
  • Stick to your treatment plan – remember to take your insulin or other diabetes medications as recommended by your care team.
  • Be as active as possible – getting regular exercise can help stop your blood sugar level rising, but you should check with your doctor first if you're taking diabetes medication, as some medicines can lead to hypoglycaemia if you exercise too much
  • Take extra care when you're ill – your care team can provide you with some "sick day rules" that outline what you can do to keep your blood sugar level under control during an illness.
  • Monitor your blood sugar level – your care team may suggest using a device to check your level at home, so you can spot an increase early and take steps to stop it.

Page last reviewed: 28/09/2015

Next review due: 28/09/2017