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The number of Americans with diabetes is on the rise—but one in four are unaware they have the disease. A report released June 10 by the Centers for Disease Control and Prevention (CDC) indicated that 9.3% of the U.S. population—more than 29 million Americans—have this disease. Among these individuals, 8.1 million, or nearly 28%, are undiagnosed. The updated figures, based on 2012 health data, represent an increase of 3 million from CDC’s 2010 estimate of 26 million people with diabetes.

CDC also reported that more than one in three U.S. adults have prediabetes, which the agency defined as fasting plasma glucose values of 100 to 125 mg/dL or HbA1c values of 5.7% to 6.4%. “Without weight loss and moderate physical activity, 15% to 30% of people with prediabetes will develop type 2 diabetes within five years,” the agency said in a statement.

In other findings for 2012, 1.7 million people age 20 or older were newly diagnosed with diabetes; the disease was also found in 208,000 people younger than 20. And certain ethnic groups, such as non-Hispanic black, Hispanic, and American Indian/Alaska Native adults, were twice as likely to have the disease as non-Hispanic white adults.

CDC’s estimate of undiagnosed diabetes came from the fasting subsample of the 2009–2012 National Health and Nutrition Examination Survey​ (NHANES). Participants lacking a history of diagnosed diabetes but with either fasting plasma glucose of at least 126 mg/dl or an HbA1c level of 6.5% or greater were considered to have undiagnosed diabetes.

“These new numbers are alarming and underscore the need for an increased focus on reducing the burden of diabetes in our country,” said Ann Albright, PhD, RD, director of CDC’s Division of Diabetes Translation, in a statement. “It’s urgent that we take swift action to effectively treat and prevent this serious disease.”