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Medically reviewed by Last updated on Feb 12, 2024.

What is Pre-Diabetes?

Harvard Health Publishing

In pre-diabetes, blood sugar levels are slightly higher than normal, but still not as high as in diabetes. If diabetes is "runaway blood sugar" think of pre-diabetes as blood sugar that is "halfway out the door." 

People almost always develop pre-diabetes before they get type 2 diabetes. The rise in blood sugar levels that is seen in pre-diabetes starts when the body begins to develop a problem called "insulin resistance." Insulin is an important hormone that helps you to process glucose (blood sugar). If usual amounts of insulin can't trigger the body to move glucose out of the bloodstream and into your cells, then you have insulin resistance. 

Once insulin resistance begins, it can worsen over time. When you have pre-diabetes, you make extra insulin to keep your sugar levels near to normal. Insulin resistance can worsen as you age, and it worsens with weight gain. If your insulin resistance progresses, eventually you can't compensate well enough by making extra insulin. When this occurs, your sugar levels will increase, and you will have diabetes. 

Depending on what a blood sugar test finds, pre-diabetes can be more specifically called "impaired glucose (sugar) tolerance" or "impaired fasting glucose." Impaired fasting glucose means that blood sugar increase after you haven't eaten for a while – for example, in the morning, before breakfast.  

Impaired glucose tolerance means that blood sugar levels reach a surprisingly high level after you eat sugar. To diagnose impaired glucose tolerance, doctors usually use what is called a "glucose tolerance test." For this test you drink a sugary solution, and then you have blood drawn after a short time. 

Having pre-diabetes does not automatically mean you will get diabetes, but it does put you at an increased risk. Pre-diabetes is also a risk factor for heart disease. Like people with type 2 diabetes, those with pre-diabetes tend to be overweight, have high blood pressure and have unhealthy cholesterol levels.


Pre-diabetes is often called a "silent" condition because it usually has no symptoms. You can have pre-diabetes for several years without knowing it. Certain risk factors increase the chance that you have pre-diabetes. These risk factors include: 

If you have one or more of these risk factors, your doctor may recommend a blood sugar test. An abnormal result is likely to be the first sign that you have pre-diabetes.


The same blood sugar tests that are used for diabetes are used to diagnose pre-diabetes. For diagnosing pre-diabetes, your doctor can order one of the following:  

In a fasting glucose test, blood sugar levels are measured after at least eight hours of not eating. Most people prefer to have the test done the morning after fasting overnight. 

In the oral glucose tolerance test, blood sugar levels are first measured after an overnight fast. You then drink a sugary solution, and two hours later another blood sample is drawn. This second test is known as a "glucose challenge." In healthy people, the glucose challenge will cause blood sugar levels to rise slightly and fall quickly. In someone with pre-diabetes or diabetes, these levels rise very high or fall slowly, so they will be abnormally high during the two-hour blood test. 

A hemoglobin A1C blood test can be done at any time during the day. It does not require fasting. The result reflects an average of your blood sugar over the preceding 3 months. 

Here is how to interpret the results of these tests (mg/dL = milligrams per deciliter):  

Fasting glucose test 

Oral glucose tolerance test 

Hemoglobin A1C test 

Expected Duration

Pre-diabetes sugar levels can remain slightly above normal, can return to normal, or can increase to a range that leads to a diagnosis of diabetes. As many as 1 in 10 people with impaired glucose tolerance will develop diabetes within one year. What happens to your pre-diabetes depends on whether you are able to prevent insulin resistance from progressing. If insulin resistance is kept in check, pre-diabetes may never become diabetes. If you do not adjust your lifestyle to increase exercise and improve diet, blood sugar levels will probably eventually rise to diabetic levels. Once this happens, medication is usually required to bring your blood sugar back to near-normal levels.


It surprises many people to learn that they may be able to prevent pre-diabetes and diabetes. To reduce your risk of both pre-diabetes and diabetes:  

If you are overweight, aim to lose weight. Even modest weight loss of 10 or 15 pounds in a person who is 200 pounds can dramatically reduce the risk of diabetes. 


The purpose for treating pre-diabetes is to prevent diabetes from setting in. The same measures recommended for preventing pre-diabetes (see above) work for treating it, too. 

The most effective treatment for pre-diabetes is to lose weight and exercise at least 30 minutes a day. Weight loss and exercise can improve insulin resistance and can lower elevated blood sugar levels so that you don't progress to develop diabetes. 

Additionally, the drug metformin (Glucophage) can lower the risk of getting diabetes, and it can add to the benefits of weight loss and exercise. Check with your doctor about whether taking metformin to prevent diabetes is a good idea for you. If your doctor feels that you have an especially high risk for progressing to diabetes, you may want to consider preventive treatment with this medication. 

When To Call a Professional

It's best to have annual glucose tests to monitor pre-diabetes. Also, look for symptoms that can suggest the development of new diabetes, such as:  


If you have pre-diabetes, you have about a 10% chance of developing type 2 diabetes within one year. Your chance of developing type 2 diabetes during your lifetime is roughly 70%.  

Fortunately, improvements in diet and exercise habits can help to delay or prevent type 2 diabetes. Research has shown that people with pre-diabetes who lose 5% to 7% of their body weight and exercise about 30 minutes a day can reduce their risk for diabetes during the next 3 years by almost 60%. 

People with pre-diabetes have a higher risk of heart disease than average, even before diabetes develops. With the onset of diabetes, your risks for heart disease and stroke increase sharply. Diabetes also leads to complications such as blindness, kidney failure, foot ulcers, pain with walking due to poor circulation, and nerve damage. That's why it's important to take action to improve your health when you are diagnosed with pre-diabetes. 

Additional Info

American Diabetes Association

American Dietetic Association

National Institute of Diabetes & Digestive & Kidney Disorders

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.