High blood sugar (hyperglycaemia)

Read NHS information about hyperglycaemia, including why it occurs, when you should see your GP, prevention and treatment, with links to other useful resources.

What is hyperglycaemia? {#overview}

What causes hyperglycaemia?

Preventing and treating hyperglycaemia

When to see your doctor

Symptoms of hyperglycaemia {#symptoms}

Hyperglycaemia causes {#causes}

Treatment for hyperglycaemia  {#treatment}

Preventing hyperglycaemia 

Complications of hyperglycaemia  {#overflow}

## What is hyperglycaemia? {#overview}
Hyperglycaemia occurs when the body can't remove glucose (sugar) from the blood and turn it into energy. It usually only happens in people with diabetes.

The [symptoms of hyperglycaemia](/health-library/conditions/hyperglycaemia/#symptoms) are similar to untreated [diabetes](/health-library/conditions/diabetes/#diabetes), and include:

-   increased thirst
-   the need to urinate frequently
-   tiredness

Over time there may be further symptoms including weight loss and blurred vision.

Your doctor will usually be able to diagnose hyperglycaemia based on a description of your symptoms. They may confirm the diagnosis by testing the level of glucose (sugar) in your blood.

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## What causes hyperglycaemia?

Hyperglycaemia is caused by an increase in blood glucose (sugar) levels. In people with diabetes, the body is unable to break glucose down into energy.

There are two types of diabetes, described below.

-   Type 1 diabetes (insulin-dependent). The body produces little or no insulin. People with type 1 diabetes require lifelong treatment to replace the insulin. They also need to check their blood glucose level regularly to prevent complications developing.
-   [Type 2 diabetes](/health-library/conditions/diabetes-type2/#introduction) (non-insulin dependent). In type 2 diabetes, either the body does not make enough insulin, or it cannot use the insulin properly (insulin resistance). This type of diabetes is often linked to [obesity](/health-library/conditions/obesity) or being overweight and mostly occurs in people who are over 40 years of age.

Insulin is the hormone that helps remove glucose from the blood and converts it to energy.

If you have diabetes, you will be advised about how to manage your blood glucose levels. However, there are some situations that can trigger an increase in blood glucose, including:

-   emotional stress
-   a change of medication
-   a wrong (or missed dose) of insulin
-   changing your diet, or eating too much
-   not exercising regularly
-   an illness, such as a cold
-   a side effect of certain medications

Read more information about the [causes of hyperglycaemia](/health-library/conditions/hyperglycaemia/#causes).

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## Preventing and treating hyperglycaemia

If you have diabetes, your diabetic care team will explain how to monitor and manage your blood glucose levels. If you have type 1 diabetes it is important not to miss or alter your dose of insulin and to maintain your fluid and food intake.

If hyperglycaemia occurs, your blood glucose levels will need to be lowered again. Increasing the dose of insulin is one way of doing this.

It is also important that you test your blood glucose levels regularly. Your doctor will advise you about when and how often your blood should be tested.

If you have uncontrolled type 2 diabetes, or if it is difficult to control, you will be carefully monitored by the healthcare professionals looking after you.

Read more information about [how hyperglycaemia is treated](/health-library/conditions/hyperglycaemia/#treatment).

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## When to see your doctor

You should visit your doctor if you or your child experiences the symptoms of hyperglycaemia, even if you haven’t been diagnosed with diabetes.

You should seek medical attention urgently if you start to experience any of the following symptoms as they may be a sign of [diabetic ketoacidosis](/health-library/conditions/diabetic-ketoacidosis) (where the body is unable to break down glucose):

-   nausea or vomiting (feeling or being sick)
-   stomach pain
-   a fruity smell on your breath, which may smell like pear drops or nail varnish
-   drowsiness or confusion
-   hyperventilation (rapid breathing)
-   [dehydration](/health-library/conditions/dehydration) (when the normal water content of your body is reduced, which can cause a headache, dry skin and a weak, rapid heartbeat)
-   unconsciousness

Diabetic ketoacidosis is a serious condition that can be life-threatening and lead to [coma](/health-library/conditions/coma) (a sleep-like state where someone is unconscious for a long period of time).

If diabetic ketoacidosis is left untreated, there may be other serious complications such as long-term damage to blood vessels, nerves and organs.

Read more information about the [complications of hyperglycaemia](/health-library/conditions/hyperglycaemia/#complications).




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## Symptoms of hyperglycaemia {#symptoms}
The symptoms of hyperglycaemia are the same as those of untreated diabetes. Diabetes is a chronic (long-term) condition that is caused by having too much glucose (sugar) in the blood.

If you have untreated [diabetes](/health-library/conditions/diabetes/#diabetes), the symptoms will develop very gradually, usually over a period of weeks or months. However, if you have hyperglycaemia, the symptoms will be more severe and come on very suddenly.

The symptoms of hyperglycaemia include:

-   being thirsty
-   having a dry mouth
-   needing to urinate frequently
-   tiredness
-   recurrent infections, such as thrush (a yeast infection)

If the symptoms of hyperglycaemia are prolonged, they may cause:

-   weight loss – as your body removes excess glucose through your urine, causing you to lose calories
-   blurred vision – caused by the lens of your eye becoming very dry

### Diabetic ketoacidosis

[Diabetic ketoacidosis](/health-library/conditions/diabetic-ketoacidosis) is a complication that can occur if hyperglycaemia is left untreated. The symptoms include:

-   nausea or vomiting (feeling or being sick)
-   stomach pain
-   a fruity smell on your breath, which may smell like pear drops or nail varnish
-   drowsiness or confusion
-   hyperventilation (rapid breathing)
-   [dehydration](/health-library/conditions/dehydration) (when the normal water content of your body is reduced, which can cause a headache, dry skin and a weak, rapid heartbeat)
-   unconsciousness

You should seek urgent medical attention if you experience any of these symptoms, as they will need to be treated in hospital.

Read more information about the [complications of hyperglycaemia](/health-library/conditions/hyperglycaemia/#complications).


## Hyperglycaemia causes {#causes}
Hyperglycaemia is caused by an increase in blood glucose (sugar) levels. This usually occurs in people with diabetes.

### Blood glucose levels

The food that you eat is digested and broken down into other substances, including a simple sugar called glucose. Glucose then enters your bloodstream.

The amount of glucose in your blood is controlled by a hormone called insulin, which is produced by your pancreas (a narrow organ that lies behind the stomach). Insulin takes glucose out of your blood and moves it into your cells, where it is broken down to produce energy.

### Diabetes

In people with [diabetes](/health-library/conditions/diabetes/#diabetes), the body is unable to break glucose down into energy. This is because there is either not enough insulin to move the glucose, or because the insulin that is there does not work properly. The glucose remains in the blood, causing a high blood glucose level.

The high blood glucose level means that glucose enters the urine. The glucose takes extra water and electrolytes (minerals and salts in the blood) with it into the urine.

This causes the [symptoms of hyperglycaemia](/health-library/conditions/hyperglycaemia/#symptoms), such as increased thirst and the need to urinate frequently. Eventually, this leads to [dehydration](/health-library/conditions/dehydration) (when the normal water content of the body is reduced).

### Hyperglycaemia triggers

If you have diabetes, your doctor will give you advice about how to manage your blood glucose levels. However, there are some events that can trigger an increase in blood glucose, including:

-   emotional stress
-   a change of medication
-   a wrong (or missed dose) of insulin
-   changing your diet, or eating too much
-   not exercising regularly
-   an illness, such as a cold

### Medications that cause hyperglycaemia

Olanzapine and risperidone are medications that are sometimes used to treat mental health conditions, such as [schizophrenia](/health-library/conditions/schizophrenia) (a condition that can cause hallucinations and delusions).

Sometimes, hyperglycaemia and diabetes can occur as a side effect of taking these medicines. If you are taking either of these, your doctor may arrange for your weight and blood glucose levels to be monitored in case you start to develop hyperglycaemia.

### Causes in children

Children with hyperglycaemia may have undiagnosed diabetes. This will usually be type 1 diabetes but it could be [type 2 diabetes](/health-library/conditions/diabetes-type2/#introduction) if the child is obese.

### Gestational diabetes

Gestational diabetes is when a woman develops diabetes during pregnancy. This may occur if your body is unable to produce enough extra insulin to meet the demands of pregnancy. This leads to an increased level of glucose in the blood.


## Treatment for hyperglycaemia  {#treatment}
How you treat hyperglycaemia will depend on what type of diabetes you have, and how you have been advised to manage your blood glucose levels.

### If you have diabetes

If you have [diabetes](/health-library/conditions/diabetes/#diabetes), you should have a diabetic care team (a team of specialists who help monitor and treat your condition). They should explain what to do if you develop hyperglycaemia.

You may be advised to:

-   increase your dose of insulin (a hormone that removes glucose from your blood so that your cells can break it down into energy)
-   change your diet – for example, you may be advised to avoid foods that cause your glucose levels to rise, such as cakes or sugary drinks
-   take more exercise, as this can reduce your blood glucose level
-   monitor your glucose level – you may be given a home testing kit to check the level of glucose in your blood

Read more information about [treating type 1 diabetes](/health-library/conditions/diabetes-type1/#treatment) and [treating type 2 diabetes](/health-library/conditions/diabetes-type2/#treatment).

### If you do not have diabetes

You should visit your doctor if you experience the [symptoms of hyperglycaemia](/health-library/conditions/hyperglycaemia/#symptoms) because you may have undiagnosed diabetes. Your doctor will test your blood glucose levels and discuss the results with you. If you have diabetes, you will be given advice about how to manage the condition.

### When to seek medical attention

You should seek medical attention urgently if you start to experience any of the following symptoms:

-   nausea or vomiting (feeling or being sick)
-   stomach pain
-   a fruity smell on your breath, which may smell like pear drops or nail varnish
-   drowsiness or confusion
-   hyperventilation (rapid breathing)
-   [dehydration](/health-library/conditions/dehydration) (when the normal water content of your body is reduced, which can cause a headache, dry skin and a weak, rapid heartbeat)
-   unconsciousness

If you have these symptoms, you may have [diabetic ketoacidosis](/health-library/conditions/diabetic-ketoacidosis), which will need hospital treatment. Read more information about the [complications of hyperglycaemia](/health-library/conditions/hyperglycaemia/#complications).


## Preventing hyperglycaemia 

If you have type 1 diabetes, in order to prevent hyperglycaemia from occurring, you will need to control your blood glucose levels by maintaining the right combination of diet and insulin injections (or tablets). Your doctor will be able to provide you with information and advice about how you can do this.

It is important not to miss or alter your dose of insulin and to maintain your fluid and food intake. It is also important that you test your blood glucose levels regularly. Your doctor will advise you when, and how often, you should test your glucose levels. If you have uncontrolled type 2 diabetes, or if it is difficult to control, you will be carefully monitored by the healthcare professionals who are looking after you.


## Complications of hyperglycaemia  {#overflow}
If left untreated, hyperglycaemia can lead to complications such as diabetic ketoacidosis or long-term damage to blood vessels, nerves and organs.

### Diabetic ketoacidosis

[Diabetic ketoacidosis](/health-library/conditions/diabetic-ketoacidosis) is when a lack of insulin means that cells cannot take glucose from the blood to use as energy. Instead, the cells start to break down fats to use as energy.

This causes ketosis (the build up of ketones in the blood) and acidosis (increased blood acidity). Ketones are chemicals that are produced by the body.

The symptoms of ketoacidosis include:

-   nausea or vomiting (feeling or being sick)
-   stomach pain
-   a fruity smell on your breath, which may smell like pear drops or nail varnish
-   drowsiness or confusion
-   hyperventilation (rapid breathing)
-   [dehydration](/health-library/conditions/dehydration) (when the normal water content of your body is reduced, which can cause a headache, dry skin and a weak, rapid heartbeat)
-   unconsciousness

If you experience any of these symptoms, seek urgent medical attention. If left untreated, ketoacidosis can lead to [coma](/health-library/conditions/coma) (a sleep-like state when someone is unconscious for a long period of time) and death.

### Treating diabetic ketoacidosis

If you have diabetic ketoacidosis, you will need to receive urgent hospital treatment. In hospital, you may be given:

-   fluids, to replace the water you have lost
-   electrolytes (minerals and salts that should be in the blood, such as potassium), to replace those you have lost
-   insulin (a hormone that removes glucose from your blood), to lower your blood glucose level

### Long-term complications

In the long-term, hyperglycaemia can increase the likelihood of complications developing as a result of [diabetes](/health-library/conditions/diabetes/#diabetes). This is because high levels of glucose in the blood can damage blood vessels, nerves and organs. If your blood glucose level is not well controlled, you may be more at risk of developing:

-   damage to your kidneys
-   damage to your eyes
-   damage to the nerves of your feet
-   heart disease (when the heart’s blood supply is blocked)
-   erection problems (in men)



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Article information

Hyperglycaemia occurs when the body can't remove glucose (sugar) from the blood and turn it into energy. (High sugar (hyperglycaemia))

Hyperglycaemia occurs when the body can't remove glucose (sugar) from the blood and turn it into energy.