The prevalence of diagnosed diabetes in US adults age 20 and older has risen from about 5.1 per cent to 6.5 per cent, according to researchers at the National Institutes of Health (NIH) and the Centres for Disease Control and Prevention (CDC), who analyzed national survey data from two periods - 1988 to 1994 and 1999 to 2002. However, the percentage of adults with undiagnosed diabetes did not change significantly over the years studied. About 2.8 per cent of US adults - one-third of those with diabetes - still don't know they have it.

The study, published in the June 2006 issue of "Diabetes Care", notes that type 2 diabetes accounts for up to 95 per cent of all diabetes cases and virtually all undiagnosed diabetes cases.

Over the years studied, about 26 per cent of adults age 20 and older continued to have impaired fasting glucose (IFG), a form of pre-diabetes. IFG, in which blood glucose measured after an overnight fast is high but not yet diagnostic of diabetes, increases the risk of heart disease as well as the risk of developing type 2 diabetes.

"It's important to know if you have pre-diabetes or undiagnosed type 2 diabetes," said Dr. Larry Blonde, chair of the National Diabetes Education Program (NDEP), jointly sponsored by the NIH, CDC, and 200 partner organizations. "You should talk to your health care professional about your risk. If your blood glucose is high but not high enough to be diagnosed as diabetes, losing weight and increasing physical activity will greatly lower your risk of getting type 2 diabetes. If you have diabetes, controlling your blood glucose, blood pressure, and cholesterol will prevent or delay the complications of diabetes," he added.

"This study updates and generally corroborates earlier analyses that were based on 2 years of NHANES data," lead author Catherine Cowie, of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) said adding, "We're seeing a rising prevalence of diagnosed diabetes that is not substantially offset by a drop in the rate of undiagnosed - about one-third of adults with diabetes still don't know they have it. Another 26 per cent of adults have a form of pre-diabetes."