Some Diabetics Drive When Blood Sugar Is Dangerously Low
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."
Results showed that the people studied stated they would drive 43-44% of the
time when they estimated their blood sugar at 60-70 mg/dL, and 38-47% of the
time when their actual blood sugar was <40 mg/dL. Approximately 50% of
drivers in each group decided to drive at least 50% of the time when their
blood sugar level was <70 mg/dL. "There are a variety of reasons that
people might drive a car even though they recognize that their glucose is
low," says Clarke. "Those can be environmental or social factors, such
as a need to pick up children, not having rapid-acting sugar available in the
car, or previous experience with low blood sugar -- in much the way that people
recognize that maybe they can drive the car when they have had two drinks and
still do OK. I think that is [fine] when you don't stress the system, but what
happens when a kid runs out in front of you? Your processing of an emergency
situation is probably at a level [that prevents you from] respond[ing]