What Is Impaired Glucose Tolerance?

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Diabetes is a serious medical condition that involves high blood sugar levels. Impaired glucose tolerance is considered prediabetes when blood sugar levels are higher than normal but too low to be classified as diabetes. People with impaired glucose tolerance are at an increased risk of developing diabetes.

Learn about impaired glucose tolerance, the symptoms, causes, diagnosis, and more.

Person with diabetes checking their blood sugar at home

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Types of Prediabetes

Prediabetes is when blood sugar levels are elevated but are too low to be diagnosed as diabetes. Prediabetes can be detected in one of the following two ways:

  • Impaired glucose tolerance: High glucose levels on a diabetes screening tool called the oral glucose tolerance test, which involves testing blood sugar levels before and after drinking a specific sugary drink
  • Impaired fasting glucose: High glucose levels on a diabetes screening tool called a fasting glucose test which involves testing blood sugar levels after a person has gone without food or drink (other than water) for at least eight hours

Impaired Glucose Tolerance Symptoms

Approximately 8 out of 10 people with prediabetes do not know they have it. This is because symptoms may not appear for years or even until the condition has escalated to diabetes.

However, there are warning signs and risk factors of prediabetes, including:


Impaired glucose tolerance, or prediabetes, is usually caused by having excess weight or obesity. It can be a precursor to type 2 diabetes.


A diabetes screening tool, the fasting glucose test, is used to diagnose impaired glucose tolerance. This blood test checks glucose levels after fasting for eight hours or more.

If fasting glucose level results are between 100 and 125 milligrams per deciliter (mg/dL), it is considered impaired glucose tolerance or prediabetes. Lower levels are normal, and higher levels are considered diabetic.

An oral glucose tolerance test may also be done. In this test, a blood sugar of 140 to 199 mg/dL is considered prediabetes, according to American Diabetes Association guidelines. Some experts consider a level of 110 mg/dL to be prediabetes.


An impaired glucose tolerance diagnosis means you are prediabetic, a precursor that could lead to diabetes. Prediabetes doesn't typically require medical treatment. Instead, the best treatment if you have impaired glucose tolerance is to make lifestyle changes, such as increasing physical activity and eating the right amount of healthy foods. Additionally, it is recommended that you be closely monitored in case medication is eventually needed.


Many people (up to 80%) with prediabetes don't know they have it, making them unaware of the necessary lifestyle changes needed to prevent diabetes.

About 25% of people diagnosed with prediabetes will be diagnosed with diabetes within five years. However, when lifestyle changes such as diet and exercise are made and weight is lost, the risk of developing diabetes decreases up to 58% for people under 60 years old and up to 71% for people over 60 years old.


Coping with impaired glucose tolerance involves making lifestyle changes around diet and exercise in hopes of reversing prediabetes and preventing type 2 diabetes.

Some lifestyle changes to jump-start weight loss and prevent diabetes include:

  • Increasing physical activity
  • Avoiding sugary and processed foods
  • Quitting smoking
  • Avoiding alcohol

Dealing with prediabetes and diabetes diagnoses can also lead to mental health challenges, such as depression or anxiety. It's essential for people with impaired glucose tolerance to seek support for any mental health challenges they may have.


Impaired glucose tolerance is prediabetes, which means blood sugar levels are higher than normal but lower than required for a diabetes diagnosis. The condition is diagnosed based on an oral glucose tolerance test, which analyzes and compares blood sugar levels after fasting and consuming a specific sugary drink.

Prediabetes can be treated by increasing physical activity, making dietary changes, and losing weight. These lifestyle changes help to decrease the risk of developing diabetes. Many people with prediabetes can make the necessary changes to improve their health and lower their risk of diabetes.

A Word From Verywell

Suspecting, being diagnosed with, and living with impaired glucose tolerance can be challenging, especially when the lifestyle changes to prevent diabetes do not always come easily. If you or someone you know is experiencing this condition, help is available. It is possible to change habits and behaviors, lose weight, and reverse impaired glucose tolerance.

Frequently Asked Questions

  • Can impaired glucose tolerance be reversed?

    Yes. Increasing physical activity levels and making dietary changes such as eating fewer processed and sugary foods can reduce blood sugar levels and reverse impaired glucose tolerance, or prediabetes. Implementing these lifestyle changes will also decrease your risk of developing diabetes.

  • Is impaired glucose tolerance the same thing as prediabetes?

    Yes. Prediabetes is when glucose levels are too high to be considered normal but not high enough to diagnose diabetes. Depending on the diagnostic test used to check glucose levels, prediabetes is referred to as impaired glucose tolerance or impaired fasting tolerance. Impaired glucose tolerance means glucose levels are high on the oral glucose tolerance test.

  • What is impaired glucose tolerance in pregnancy?

    The oral glucose tolerance test is a standard test administered during pregnancy to screen for gestational diabetes. Impaired glucose tolerance in pregnancy means that the blood sugar levels are elevated. These levels are higher than normal but not high enough to be diagnosed with gestational diabetes. This means there is an increased risk of developing gestational diabetes.

12 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Centers for Disease Control and Prevention. Prediabetes - your chance to prevent type 2 diabetes.

  3. American Diabetes Association. Diagnosis.

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  5. Centers for Disease Control and Prevention. The surprising truth about prediabetes.

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  7. American Diabetes Association. 2. Classification and Diagnosis of Diabetes: Standards of Care in Diabetes-2023Diabetes Care. 2023;46(Suppl 1):S19-S40. doi:10.2337/dc23-S002

  8. American Diabetes Association. Prediabetes.

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  10. Harvard Medical School. Many miss prediabetes wake-up call.

  11. Harvard School of Public Health. Simple steps to preventing diabetes.

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By Ashley Olivine, Ph.D., MPH
Dr. Ashley Olivine is a health psychologist and public health professional with over a decade of experience serving clients in the clinical setting and private practice. She has also researched a wide variety psychology and public health topics such as the management of health risk factors, chronic illness, maternal and child wellbeing, and child development.