Testing for Prediabetes

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Testing for Prediabetes

Contributor: Dr. Rita Kalyani, MD, MHS

Prediabetes occurs when blood glucose levels are higher than normal but not yet high enough to be considered diabetes. Often persons with prediabetes do not have any symptoms, and most people with prediabetes don’t know they have it. Prediabetes can lead to heart disease, stroke, nerve damage, and type 2 diabetes, the most common form of diabetes. People with prediabetes may be able to delay or prevent the development of type 2 diabetes with appropriate changes to diet and lifestyle or, in some people, by taking metformin.

What You Need to Know

According to the American Diabetes Association, persons are diagnosed with prediabetes if any of the following tests are abnormal:

  • Fasting blood glucose: People who have a mildly high blood glucose after not eating for at least 8 hours have impaired fasting glucose. After fasting, the blood glucose levels in a person without diabetes are usually less than 100 mg/dL (5.6 mmol/L). A person with diabetes has blood glucose levels of 126 mg/dL (7.0 mmol/L) or higher. People who don’t fit into either category— with levels between 100 and 125 mg/dL (between 5.6 and 6.9 mmol/L)—are described as having prediabetes.
  • OGTT: People who experience an abnormal rise in blood glucose after consuming a concentrated sugar drink have impaired glucose tolerance. Health care providers diagnose this condition by testing a person’s blood glucose 2 hours after he or she consumes a sweet drink containing 75 grams of glucose. People without diabetes have blood glucose levels less than 140 mg/dL (7.8 mmol/L). A person with diabetes has blood glucose levels 200 mg/ dL (11.1 mmol/L) or higher. Persons whose blood glucose levels fall in the middle, between 140 and 199 mg/dL (between 7.8 and 11.0 mmol/L), have prediabetes.
  • Hemoglobin A1C: People with hemoglobin A1C levels between 5.7% to 6.4% (between 39 to 47 mmol/mol) fall into the “category of high risk for diabetes.” People with normal blood glucose levels have hemoglobin A1C levels below 5.7% (39 mmol/mol). People with diabetes have levels 6.5% (48 mmol/mol) or greater. Someone whose A1C levels fall between the two cutoffs are in a category of high risk.

Should I Be Screened for Prediabetes?

Talk to your health care provider, particularly if you

  • are 45 years or older;
  • are overweight or obese (with a BMI of 25 kg/m or greater; in Asians, 23 kg/m or greater) at any age;
  • have a family history of diabetes in a first-degree relative (parents, siblings, children);
  • are inactive during the day, with little or no physical activity;
  • have a history of gestational diabetes;
  • or belong to a minority racial or ethnic group, including Hispanics and African Americans.

Simple online tests are available for you to take and determine if you are at risk for prediabetes or diabetes. For example, the Centers for Disease Control and Prevention (https://www.cdc.gov/diabetes/prevention/pdf/Prediabetes-Risk-Test-Final.pdf) and the American Diabetes Association (http://www.diabetes.org/are-you-at-risk/diabetes-risk-test) each have their own version. Talk to your health care provider if your score indicates that you might be at risk. A blood test will be required to provide a definite diagnosis of prediabetes.

Why Is It Important to Diagnose Prediabetes?

Don’t let the “pre” in prediabetes lead you to believe that it’s not really a problem. There are steps that you can take now to prevent prediabetes from becoming type 2 diabetes and to reduce the risk of heart attack and stroke. A prediabetes diagnosis does not mean you will definitely develop type 2 diabetes—healthy lifestyle changes or taking metformin can dramatically reduce your risk of developing diabetes and delay its onset. A landmark study called the Diabetes Prevention Program demonstrated that among persons with prediabetes, intensive lifestyle changes dramatically reduced the development of diabetes by 58% (or approximately half). These changes may include

  • eating a healthy diet,
  • exercising regularly (for example, 30 minutes of brisk walking per day, 5 days a week),
  • and losing weight (7% of body weight, which, for example, would be about 14 pounds in a 200-pound person).

In some cases of prediabetes where lifestyle changes are not feasible or practical, the medication metformin may be prescribed. It is particularly effective for people with severe obesity or a history of gestational diabetes. However, metformin is not currently approved by the Food and Drug Administration for the treatment of prediabetes.

What Does It All Mean?

  • Many different tests can be used to diagnose prediabetes. These are the same as those used to diagnose diabetes but use lower glucose cutoffs to define an abnormal test.
  • Prediabetes is not just a “precursor” state to diabetes. It can be related to the development of multiple medical conditions, such as heart disease, stroke, and even nerve damage.
  • Lifestyle changes, including dietary modifications and regular physical activity that result in modest weight loss (7%), can dramatically reduce the development of diabetes in persons with prediabetes. Ask your health care provider about programs based on the Diabetes Prevention Program that may be in your area. Some of these may be covered by insurance.
  • Without appropriate lifestyle changes or metformin treatment, many people with prediabetes will develop type 2 diabetes within 5 years. Even more concerning, the majority of people with prediabetes will go on to develop diabetes in their lifetimes.


Diabetes Head To ToeDr. Rita Kalyani is an Associate Professor of Medicine at Johns Hopkins University School of Medicine in the Division of Endocrinology, Diabetes & Metabolism. She is an active clinician in the Johns Hopkins Comprehensive Diabetes Center. Dr. Kalyani directs the Diabetes Management Service for Johns Hopkins’ Total Pancreatectomy Islet Auto Transplant Program. She is a new member of the DiabetesSisters Board of Directors.

This excerpt is taken from "Diabetes Head to Toe: Everything You Need to Know about Diagnosis, Treatment, and Living with Diabetes" by Dr. Rita Kalyani, Dr. Mark Corriere, Dr. Thomas Donner, and Dr. Michael Quartuccio. Published by Johns Hopkins University Press © 2018. Reprinted by permission of the publisher.