Hyperglycaemia (high blood glucose)

Hyperglycaemia (also known as a ‘hyper’) is the medical name for high blood glucose (sugar). It is a common problem for people with diabetes.

Key points about hyperglycaemia

  1. Hyperglycaemia occurs when there is too much glucose (sugar) in your bloodstream.
  2. No matter how careful you are, if you have diabetes, you will get hyperglycaemia from time to time.
  3. Regularly checking blood glucose levels and recognising and treating hyperglycaemia is an important part of diabetes management.
  4. Occasional mild episodes are not usually a cause for concern and can be treated quite easily or return to normal on their own.
  5. However, if blood glucose levels stay high for longer periods this can lead to permanent damage to parts of your body, such as your heart, brain, eyes, nerves, kidneys and blood vessels.
  6. If blood glucose levels rise dangerously high this can lead to life-threatening complications such as diabetic ketoacidosis and hyperosmolar hyperglycaemic state. 
Seek urgent medical advice if you have high blood glucose and experience the following symptoms:
  • feeling sick (nausea) or being sick (vomiting)
  • abdominal (tummy) pain
  • diarrhoea (runny poo)
  • rapid, deep breathing
  • a fever (38°C or above) for more than 24 hours
  • signs of dehydration, such as a headache, dry skin and a weak, rapid heartbeat
  • difficulty staying awake.

These symptoms could be a sign of more serious complications of hyperglycaemia, such as diabetic ketoacidosis or a hyperosmolar hyperglycaemic state, and you may need to be looked after in hospital.

What is hyperglycaemia? 

Hyperglycaemia happens when there is too much glucose in your bloodstream. Normally the human body keeps its blood glucose level very stable (between 4mmol/L to 7 mmol/L). Hyperglycaemia is defined as:

  • blood glucose levels greater than 7.0 mmol/L (126 mg/dl) when fasting
  • blood glucose levels greater than 11.1 mmol/L (200 mg/dl) 2 hours after meals. 

If your blood glucose levels are more than 7 mmol/L for an extended period it can start to cause damage. However, you might not feel any symptoms until blood glucose levels go over 11.0 mmol/L. Regular monitoring of your blood glucose levels is the best way to check if your blood glucose levels are within the ideal range. Read more about blood glucose testing.

Hyperglycemia – causes, symptoms and treatment of hyperglycemia

(Diabetes.co.uk, 2011)

What causes hyperglycaemia? 

The underlying cause of hyperglycaemia is the loss of insulin-producing cells in your pancreas or your body developing resistance to insulin. 

More immediate reasons for hyperglycaemia include:

  • missing a dose of diabetic medication, tablets or insulin
  • eating more carbohydrates than your body and/or medication can manage
  • being physically or emotionally stressed (eg, due to injury, surgery or anxiety)
  • having an infection.

What are the symptoms of hyperglycaemia?

The main 3 symptoms of high blood glucose levels are increased urination (peeing), increased thirst and increased hunger. 

High blood glucose levels can also cause:

  • weakness or feeling tired
  • loss of weight
  • vision blurring
  • recurring infections, such as thrush, bladder infections and skin infections
  • tummy pain
  • feeling or being sick
  • breath that smells ‘fruity’. 

Symptoms of hyperglycaemia in people with diabetes tend to develop slowly over a few days or weeks. There may be no symptoms until your blood sugar level is very high – over 11 mmol/L. 

Symptoms of hyperglycaemia can also be caused by undiagnosed diabetes, so see a GP if you have these symptoms and are not diagnosed as diabetic.

Is hyperglycaemia serious?

Hyperglycaemia can be serious in the following cases:

  • If blood glucose levels stay high for long periods of time – this can result in permanent damage to parts of your body such as your heart, brain, eyes, nerves, kidneys and blood vessels.
  • If blood glucose levels rise dangerously high – this can lead to life-threatening complications such as diabetic ketoacidosis and hyperosmolar hyperglycaemic state.

Learn more about diabetes complications.

How is hyperglycaemia treated?

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 glucose levels within a healthy range. 

You may be advised to:

  • adjust the foods you eat – eg, avoid foods such as cakes or sugary drinks
  • drink plenty of sugar-free fluids – to help keep you well hydrated
  • exercise more often – even gentle, regular exercise such as walking can lower your blood sugar level
  • if you use insulin, adjust your dose – your healthcare team can give you specific advice about how to do this.

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

How can I prevent hyperglycaemia?

To reduce your risk of severe or prolonged hyperglycaemia: 

  • monitor your blood glucose level regularly
  • be careful with what you eat – be particularly aware of how snacking and eating sugary foods or carbohydrates can affect your blood glucose levels
  • stick to your management plan – take diabetes medicines as and when directed
  • be as active as possible – getting regular exercise can help stop your blood glucose level rising, but you should check with your doctor first if you're taking diabetes medication, as some medicines can lead to hypoglycaemia (low blood glucose) if you exercise too much.
  • take extra care when you're ill – see our page on having a diabetes sick day plan

Learn more 

Hyperglycaemia (high blood sugar) NHS, UK 
Hyperglycaemia high blood glucose (hyper) and type 2 diabetes Diabetes NZ


  1. Diabetes and hyperglycemia diabetes.co.uk

Information for healthcare providers

Screening and diagnosis of type 2 diabetes Ministry of Health, NZ and NZ Society for the Study of Diabetes, 2020
Type 2 diabetes and the management of hyperglycaemia
 Research Review, NZ, 2019 
Guidance on the management of type 2 diabetes NZ Guidelines Group, 2011
ANZCOR Guideline 9.2.9 – first aid management of a diabetic emergency Australian and NZ Committee on Resuscitation, 2017

Reviewed by

Dr Alice Miller trained as a GP in the UK and has been working in New Zealand since 2013. She has undertaken extra study in diabetes, sexual and reproductive healthcare, and skin cancer medicine. Alice has a special interest in preventative health and self-care, which she is building on by studying for the Diploma of Public Health with the University of Otago in Wellington.
Credits: Health Navigator Editorial Team. Reviewed By: Dr Alice Miller, FRNZCGP, Wellington Last reviewed: 08 Mar 2021