An estimated 4.9 million adults in the United States have undiagnosed diabetes. Because the average patient has no symptoms for up to 12 years, one in five will develop diabetic retinopathy before seeking medical care. Other common complications of diabetes are peripheral sensory neuropathy and nephropathy. It is uncertain how many patients with undiagnosed diabetes are affected. Koopman and colleagues estimated the prevalence of neuropathy and nephropathy in patients with undiagnosed diabetes using data from the most recent U.S. National Health and Nutrition Examination Survey (NHANES).

The cross-sectional study included a subset of 2,337 persons who were 40 years or older, had no history of stroke, and participated in the NHANES from 1999 to 2002. Participants provided information about demographics, income, education, and health care access, as well as a self-rated health status. They also underwent a physical examination and laboratory testing. Diagnosed diabetes was defined as being given a prior diagnosis of diabetes by a health care professional or being prescribed a medication to regulate blood glucose. Participants who met neither of those criteria but had a fasting plasma glucose level of 126 mg per dL (7.0 mmol per L) or higher were determined to have had undiagnosed diabetes. A positive screening test for nephropathy was a spot urine albumin-to-creatinine ratio of 30 mg per g or higher. A positive screen for peripheral neuropathy was the inability to feel pressure from a Semmes-Weinstein monofilament test more than once at the same site on the foot.

Overall, 271 participants had diagnosed diabetes and 132 participants had undiagnosed diabetes. A total of 399 participants had screening tests positive for nephropathy, and 332 had tests positive for neuropathy; participants with undiagnosed diabetes were significantly more likely to have positive tests than participants without diabetes. The percentage of participants with undiagnosed diabetes found to have nephropathy (24.9 percent) was similar to that found in those with diagnosed diabetes (28.0 percent). A higher percentage of persons with undiagnosed diabetes had peripheral neuropathy compared with persons with diagnosed diabetes (21.5 and 19.2 percent, respectively). A logistic regression analysis that adjusted for age and hypertensive status did not significantly alter these findings.

The authors conclude that the prevalence of nephropathy and peripheral neuropathy in patients 40 years or older with undiagnosed diabetes is similar to that in patients who are already diagnosed with diabetes. This information adds to the evidence that preclinical diabetes is associated with significant morbidity. These findings may indicate the need for a reexamination of current policies on screening asymptomatic patients at high risk of diabetes.

editor’s note: In 2003, the U.S. Preventive Services Task Force recommended screening for type 2 diabetes in adults with hypertension or hyperlipidemia, but found insufficient evidence to determine whether routine screening of otherwise healthy populations provides an additional benefit compared with initiating treatment after clinical diagnosis.¹ In contrast, the American Diabetes Association suggests screening asymptomatic adults 45 years or older every three years, especially if they are overweight.² Although experts continue to debate the merits of screening, there should be no debate that once diabetes is diagnosed, patients should be treated aggressively to delay the development of these common vascular complications.—k.w.l.