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Some Diabetics Drive When Blood Sugar Is Dangerously Low

WebMD Health News

Nov. 16, 1999 (Atlanta) -- Many patients with type 1 diabetes misjudge when their blood sugar is too low to safely drive a car, according to a study published in a recent issue of The Journal of the American Medical Association. Equally worrisome is a finding that some people with type 1 diabetes choose to drive even when they know that their blood sugar, or glucose, levels may be dangerously low.

"What this study showed is that a large percentage of the time, people with type 1 diabetes were making decisions to drive the car when their blood sugars were in a range that could impair their ability to drive safely," researcher William Clarke, MD, tells WebMD. Clarke is a professor of pediatrics at the University of Virginia Health Sciences Center in Charlottesville.

Other studies have shown that driving performance deteriorates significantly when a person's blood sugar is reduced to between 47 and 65 mg/dL. "At these levels of mild to moderate hypoglycemia, steering was disrupted, resulting in swerving, spinning, and increased time across the midline and off the road," the researchers write. Their study adds additional information to this disturbing picture.

For the study, two separate groups of patients with type 1 diabetes were enrolled from four medical centers. To participate, they had to be familiar with self-monitoring of blood sugar levels, and they had to measure their levels at least twice daily. Each person studied was trained to use a hand-held computer to do the following as they went through their normal daily activities: 1) record information about their symptoms; 2) perform two tests of thinking ability; 3) rate what they thought was their degree of impairment in performing each test; 4) enter whether their most recent insulin, food, and exercise were more, less, or usual in amount; 5) estimate their current blood sugar level; and 6) answer the question, "Based on your current blood glucose, would you drive now?"; and 7) obtain a blood sample and measure their actual blood sugar levels.

"We have never before had that kind of information from patients in their natural environment," says Clarke. "We can ask people questions about what they 'would' do, what they 'might' do, [when they're] in a lab situation or in a hospital bed, but these individuals were in their natural environment performing their everyday tasks."

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