Pre-diabetes Impaired Glucose Tolerance

Authored by , Reviewed by Dr Colin Tidy | Last edited | Meets Patient’s editorial guidelines

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In pre-diabetes (impaired glucose tolerance), your blood sugar (glucose) is raised beyond the normal range. Whilst this raised glucose level is not so high that you have type 2 diabetes, you are at increased risk of developing type 2 diabetes when you have pre-diabetes.

You are also at increased risk of developing conditions such as heart disease, peripheral arterial disease and stroke (cardiovascular diseases). If pre-diabetes is treated, it can help to prevent the development of type 2 diabetes and cardiovascular disease. The most effective treatment is lifestyle changes, including eating a healthy balanced diet, losing weight if you are overweight, and doing regular physical activity.

What is pre-diabetes?

Dr Partha Kar

If you have pre-diabetes (impaired glucose tolerance), your blood sugar (glucose) is raised beyond the normal range but it is not so high that you have diabetes. However, if you have pre-diabetes you are at risk of developing type 2 diabetes.

Between 1 and 3 out of every 4 people with pre-diabetes will develop diabetes within ten years.

It is also thought that having pre-diabetes increases your risk of developing conditions such as heart disease, peripheral arterial disease and stroke (cardiovascular diseases). Also, people who have pre-diabetes are more likely also to have other risk factors for cardiovascular disease, including high blood pressure, raised cholesterol levels, being overweight, etc. See the separate leaflets called Cardiovascular Disease (Atheroma) and Cardiovascular Health Risk Assessment for more details.

The World Health Organization (WHO) defines someone as having pre-diabetes if they have:

  • A fasting blood glucose of less than 7 mmol/L; and
  • A blood glucose of 7.8 mmol/L or more but less than 11.1 mmol/L after a two-hour oral glucose tolerance test.

However, the glucose tolerance test is rarely used now. The most commonly used test to identify pre-diabetes is now the HbA1c blood test. The WHO and the National Institute for Health and Care Excellence (NICE) have recommended that an HbA1c blood test level of 42-47 mmol/mol (6.0-6.4%) indicates a high risk of diabetes.


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The WHO has also said that someone has impaired fasting glycaemia if they have:

  • A fasting blood glucose between 6.1 to 6.9 mmol/L; and
  • A blood glucose of less than 7.8 mmol/L after a two-hour oral glucose tolerance test.

NICE states that someone with a fasting blood glucose of 5.5-6.9 mmol/L is at high risk of developing type 2 diabetes.

If you have impaired fasting glycaemia, you are also thought to have an increased risk of developing diabetes. Your risk of developing cardiovascular disease is also increased but this seems to be lower than if you have pre-diabetes (impaired glucose tolerance). The rest of this leaflet is about pre-diabetes.

Many people have pre-diabetes (impaired glucose tolerance) and because there are no symptoms, they do not know that they have it. Diabetes UK estimates that around seven million people in the UK have pre-diabetes.

Can you reverse pre-diabetes?

Dr Sarah Jarvis MBE

Pre-diabetes (impaired glucose tolerance) develops for the same reasons as type 2 diabetes (see above). There are various things that can increase your risk of developing pre-diabetes. They are the same risk factors as those for type 2 diabetes. They include:

People with pre-diabetes (impaired glucose tolerance) usually have no symptoms. You are often found to have pre-diabetes after blood tests taken for another reason show that you have a raised blood sugar (glucose) level. Sometimes, your doctor may suggest that a screening blood test should be taken to check your blood glucose because they are worried that you may have some risk factors for pre-diabetes or diabetes. For example, if you have high cholesterol levels, are overweight or have high blood pressure, or if you have had a heart attack or stroke, your doctor may suggest that you have a blood test to check your blood glucose.

Pre-diabetes is now most often diagnosed using a blood test called HbA1c. See the separate leaflet called Tests for Blood Sugar (Glucose) and HbA1c for more details. An HbA1c value of 48 mmol/mol (6.5%) or above is recommended as the blood level for diagnosing diabetes. People with an HbA1c level of 42-47 mmol/mol (6.0-6.4%) are often said to have pre-diabetes because they are at increased risk of diabetes and cardiovascular disease.

Another test to diagnose pre-diabetes is the glucose tolerance test but this is much less often used now. Read more in the separate leaflet called Glucose Tolerance Test.

There is increasing evidence that if pre-diabetes (impaired glucose tolerance) is treated, the progression to diabetes can be prevented. Also, it may be possible to prevent cardiovascular disease from developing. So, it is important to know if you have pre-diabetes and to treat it in order to reduce your risk of developing diabetes and cardiovascular disease. Treatments that have been suggested include lifestyle changes and treatments with medicines.

It is also very important to have a regular blood test to recheck your blood sugar (glucose) level in case you develop diabetes. The frequency of the blood test will vary but you should discuss this with your doctor. A blood glucose test at least once each year is usually recommended.

Referral for help and support

The NHS in England has developed the NHS Diabetes Prevention Programme for people with pre-diabetes. This provides personalised support from a group of healthcare professionals.

If you are diagnosed with pre-diabetes and live in England, you should be offered referral to this service. It involves at least 13 sessions over about 9 months, each lasting 1-2 hours. You will be supported to set and achieve goals and make positive changes to reduce your risk of developing type 2 diabetes. Most of the sessions will be run as face-to-face groups with other people who also have pre-diabetes and led by one or more experts.

Lifestyle changes

Lifestyle changes have been found to be the most effective way to stop pre-diabetes from developing into diabetes. Losing weight if you are overweight, and increasing your levels of physical activity, can help to reduce insulin resistance and therefore make the insulin that is produced more effective at controlling your blood glucose levels.

If you have pre-diabetes, you should:

  • Eat a healthy balanced diet. Your practice nurse and/or a dietician will give details on how to eat a healthy diet. The diet is the same as recommended for everyone. The idea that you need special foods if you have pre-diabetes or diabetes is a myth. Basically, you should aim to eat a diet low in fat, high in fibre and with plenty of fruit and vegetables:
    • Starchy foods contain carbohydrates. Standard advice is that you should continue to eat some starchy foods, although you should focus on wholegrain and wholewheat versions - so-called 'complex carbohydrates'. These tend to have a lower glycaemic index (GI) which means they are more slowly absorbed and do not raise your blood sugar as rapidly.
    • However, what many people don't realise is that starchy carbs like bread, potatoes or breakfast cereals digest down into a surprisingly large amount of sugar. More and more people are discovering that by reducing the carbs (both sugary and starchy) in their diet, it is possible to lose weight and reduce blood sugar (glucose). If you do include carbs in your diet, choose complex carbs.
    • See the separate leaflet called Type 2 Diabetes Diet for more details.
  • Lose weight if you are overweight. Getting to a perfect weight is unrealistic for many people. However, if you are overweight or obese then losing some weight will help to reduce your blood glucose level (and have other health benefits too). See the separate leaflet called Weight Loss (Weight Reduction).
  • Do some physical activity regularly. If you are able, a minimum of 30 minutes of physical activity at least five times a week is advised. For example, walking, swimming, cycling, jogging, dancing - anything that makes you at least mildly out of breath and mildly sweaty. You can start slowly and build up. You can also spread the activity over the day - for example, two 15-minute spells per day. Regular physical activity also reduces your risk of having a heart attack or stroke. Always check with your doctor that it is safe to start exercising if you have been inactive for a long period. See the separate leaflet called Exercise and Physical Activity.

Public Health England advises 150 minutes of physical activity each week, in bouts of 10 minutes or more. This might feel like a tall order, but it can be done in a way that becomes an enjoyable part of your life. Honestly.

— Dr Mary Harding, The best forms of exercise for those who hate the gym

There are also other lifestyle changes that you can make to reduce your cardiovascular disease risk. These include:

Make sure that your blood pressure stays within the normal range. Have your blood pressure checked regularly with your practice nurse.

Also, discuss with your doctor or practice nurse if you need a cholesterol check and/or treatment to lower your cholesterol level.

Treatments with medicines

A number of medical trials have looked at the use of various treatments with medicines for people with pre-diabetes to see if they can help to prevent diabetes and cardiovascular disease. Medicines that have been trialled include metformin, acarbose, a group of medicines called angiotensin-converting enzyme (ACE) inhibitors and another group of medicines called angiotensin-II receptor antagonists (also known as angiotensin receptor blockers).

Lifestyle changes (as indicated above) are the most important thing if you are found to have pre-diabetes. However, the National Institute for Health and Care Excellence (NICE) has recommended that metformin should be used if a lifestyle-change programme isn't successful or isn't possible because of a disability or medical reasons. A medicine called orlistat may also be recommended to help lose weight and therefore reduce the risk of developing diabetes.

If you are found to have pre-diabetes (impaired glucose tolerance), it is important that you be followed up regularly by your doctor. This will usually mean a blood test to check your fasting blood sugar (glucose) level at least once a year. This is to make sure that you have not developed diabetes. Your doctor is also likely to keep a check on any other risk factors that you may have for cardiovascular disease. So, they may monitor your weight and your blood pressure and also suggest a blood test to check your cholesterol and triglyceride levels.

In the meantime, if you develop any symptoms of diabetes, you should visit your doctor sooner. Symptoms include excess thirst, passing large amounts of urine, tiredness, weight loss and feeling generally unwell. Symptoms tend to develop quite slowly, over weeks or months.

The same things that can help prevent type 2 diabetes can help prevent pre-diabetes (impaired glucose tolerance). These include:

  • Eating a healthy balanced diet.
  • Losing weight if you are overweight.
  • Doing some physical activity regularly.

If you do develop type 2 diabetes, it's important to go for regular check-ups to ensure it doesn't worsen.

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Further reading and references