A condition in which blood glucose levels are elevated, but not yet within the diabetic range. Prediabetes is also known as impaired fasting glucose (IFG) or impaired glucose tolerance (IGT). The new term was inaugurated by the U.S. Department of Health and Human Services (HHS) and the American Diabetes Association (ADA) in March 2002 to promote public understanding of this increasingly widespread problem. According to the Centers for Disease Control and Prevention (CDC), roughly 84.1 million Americans have prediabetes. Studies have shown that most people with blood glucose levels in the prediabetes range go on to develop type 2 diabetes within 10 years; the condition also raises the risk of having a heart attack or stroke by 50 percent. Prediabetes can be controlled, and in many cases even reversed, through lifestyle changes.
Prediabetes can be detected by a number of standard tests currently used to diagnose diabetes. In the fasting plasma glucose test (FPG), a person fasts overnight and then has blood drawn for testing first thing in the morning, before he eats. Until 2003, a fasting blood glucose level under 110 mg/dl was considered to be normal and fasting blood glucose in the range of 110 to 125 mg/dl indicated impaired fasting glucose (IFG), or prediabetes. In late 2003, an international expert panel recommended that the cutoff be lowered to 100 mg/dl, so now people with a fasting blood glucose level of 100 to 125 mg/dl are considered to have prediabetes. A fasting blood glucose level over 125 mg/dl indicates diabetes. (A second test must be done on a subsequent day to confirm a diagnosis of diabetes.)
In the oral glucose tolerance test (OGTT), a person’s blood glucose is tested once after an overnight fast and again two hours after he has consumed a special, glucose-rich drink. A normal blood glucose level two hours after the drink would be below 140 mg/dl; an elevated blood glucose level in the range of 140 to 199 mg/dl indicates impaired glucose tolerance, or prediabetes. A blood glucose level 200 mg/dl or higher two hours after the drink indicates diabetes. (Again, a second test must be done on a subsequent day to confirm diabetes.)
Additionally, an HbA1c result (a test indicating blood glucose control over the previous 2–3 months) 5.7 percent to 6.4 percent is considered to be prediabetes, while a result of 6.5 percent or higher indicates diabetes. (Again, a second test is required to confirm the diagnosis.)
Who is at risk for prediabetes? An expert panel convened by HHS and the ADA recommends that physicians begin screening all people age 45 and up for the condition. All overweight adults should also be screened if they have one or more of the following risk factors for diabetes: high blood pressure, a family history of diabetes, low high-density lipoprotein (HDL, or “good”) cholesterol and high triglycerides, a history of gestational diabetes or giving birth to a baby over 9 pounds, or belonging to one of the racial or ethnic groups that is at increased risk for type 2 diabetes (African-Americans, Native Americans, Asian Americans/Pacific Islanders, and Hispanic Americans/Latinos). If a person is tested for prediabetes and his results are within the normal range, the ADA recommends that he be retested every three years (unless his doctor recommends testing more frequently). If a person is diagnosed with prediabetes, he should be screened for type 2 diabetes every one to two years.
Prediabetes can also affect children and adolescents. A research letter published in JAMA (the Journal of the American Medical Association) in July 2016 found that nearly 18 percent of adolescents (age 12–19) tested had blood glucose levels within the prediabetes range. Currently, not much is known about how to prevent or delay the onset of type 2 diabetes in children. The widespread screening of younger people for prediabetes, therefore, is not currently called for by major health organizations. However, in 2000, the American Academy of Pediatrics recommended diabetes testing for obese children who also have two or more of the additional risk factors for diabetes mentioned above.
In adults who have been diagnosed with prediabetes, lifestyle changes can delay or prevent the development of full-blown type 2 diabetes. Results from the Diabetes Prevention Program, a study conducted by HHS and involving more than 3,000 participants, showed that a 5 percent to 7 percent weight loss lowered the incidence of type 2 diabetes by 58 percent. The weight loss was achieved through dieting (cutting fat and calories) as well as exercising moderately (most participants chose walking) for at least 150 minutes a week. Use of the oral diabetes drug metformin (brand name Glucophage and others) also helped to delay the onset of diabetes in some study participants; however, it was not as effective as diet and exercise.