A study published in the August 25 Journal of the American Medical Association (JAMA) reports that people with type 1 diabetes "may not judge correctly when their blood sugar levels are too low and may consider driving with a low BG." In the study, "low" was defined as less than 70 mg/dl.

Two separate groups of patients were recruited two years apart from four academic medical centers, totaling 158 type 1 subjects. The subjects would enter data into hand-held computers to record how they felt, what they estimated their blood sugars to be, and whether they would make the decision to drive. Then, they would measure their blood sugar. They did this several times a day for a few weeks, and were never instructed about safe driving ranges before or during the study.

When actual blood sugars were 60 to 70 mg/dl, subjects said they would drive nearly 45 percent of the time.

"Our data suggest that persons with type 1 diabetes may not judge correctly when their blood glucose is too low to permit safe driving..." writes William Clarke, MD, of the University of Virginia Health Sciences Center. Clarke adds that people with diabetes should be aware of the danger of relying on their ability to detect low blood sugar without testing it.

I Have to Get to Work

Miriam E. Tucker, a medical journalist in Rockville, Maryland, who has type 1 diabetes, feels frustrated by studies like the one in JAMA.

"I have to get to work or wherever I'm going," says Tucker. "I have sugar in my car and I've driven plenty of times with low blood sugars. If it's low enough I'll eat sugar. You can eat and drive. The two are not mutually exclusive."

Tucker says that the authors of the JAMA study make it sound like people with diabetes irresponsibly get into a car and do not think about how they are feeling.

"The message that gets out with these kinds of studies is, 'Oh my God, all these diabetics are out driving around.' It is possible to treat your low blood sugar while you are living your life and moving around."

Tucker emphasizes that she eats sugar whenever she is feeling low and always keeps glucose tablets and hard candy in her car in an easy-to-reach place.

Speaking with DIABETES HEALTH, Clarke says that people with diabetes should instead pull over to the side of the road, turn off the engine, engage the brake and treat the low BG.

"Then, they should wait 10 to 15 minutes until their brain recovers from the low BG," he says. "The recovery of cognitive function lags behind the recovery of a low BG."

Poor Judgment To Drive With a Low Blood Sugar

John Hunt, MB, BS, FRCP, a clinical associate professor at the University of British Columbia's division of endocrinology, says that some people with diabetes lose judgment as the first symptom of low blood sugar and therefore do not recognize that they are low, do not eat, and may finish up with severe hypoglycemia.

"I despair for these people," says Hunt, who tells his patients who drive to always carry sugar in the car where they can reach it easily, like the glove compartment or on the seat beside them. "I don't know how many people actually follow this advice, and I hate to ask. The point is that [people with diabetes who drive] have a responsibility to themselves, other drivers and their families to take all reasonable precautions to prevent hypoglycemia while driving in the first place."

Kriss Halpern, a southern California attorney with type 1 diabetes, says that no person with diabetes should drive if his or her BGs are below 50 mg/dl (see "Diabetes and Driving Responsibilities"). Although the JAMA study did not designate an unsafe BG driving level, Clarke suggests that people treat BGs that are 80 mg/dl or lower to prevent them from falling lower during driving.

Clarke points to a similar study of his that was published in a February 1993 issue of Diabetes ("Driving Decrements in Type 1 Diabetes During Moderate Hypoglycemia"). In that study, Clarke and colleagues at the University of Virginia found that BG levels between 47 and 65 mg/dl were associated with driving problems in 35 percent of the patients. Clarke wrote that people with diabetes "should be instructed not to drive without treating blood glucose below [65 mg/dl]."

Clarke adds that an additional study on low blood sugars and driving will be published in Diabetes Care later this fall. This study, like the ones in Diabetes and JAMA, will "further demonstrate changes in symptoms and in physiologic responses with BGs under 70 mg/dl."

Don't Blame The Victim

Joan Hoover, DIABETES HEALTH's patient advocate advisor from Chevy Chase, Maryland, is disappointed with the JAMA study.

"Diabetes does not make you stupid," she argues. "Diabetic drivers are not eager to endanger their own lives and the lives of others."

Hoover calls into question the conclusions reached by Clarke and colleagues at the University of Virginia.

"I'm disturbed by the implication that diabetic driving problems are a result of conscious, bad decisions on the part of the diabetic driver," says Hoover. "Hypoglycemia can have many origins, most of which are poorly understood. Neuropathy can alter the signals of an impending insulin reaction. Also, followers of the DCCT often tend to keep their glucose levels dangerously low."

Hoover adds that any effort to "blame the victim" for hypoglycemia-related motor accidents serves only to "misinform and to push the eventual solution just that much further out of reach."

Diane Bayliss of Brockville, Ontario, feels that there are many medical conditions that can develop while driving, and that low blood sugar is just one of them.

"Just as people with diabetes can have hypoglycemia, a nondiabetic person can experience a heart attack," says Bayliss. "I would think that a person with diabetes would be at less risk of creating an accident because he or she is so aware of the health and potential risk factors."

Doctors Should Counsel Their Patients

The JAMA article points out that no study has ever demonstrated a higher incidence of automobile crashes among people with diabetes when compared to the general population. Clarke still feels that health care professionals should counsel their patients about the risk of driving with hypoglycemia and the importance of measuring blood glucose before driving.

"If surveyed, I would bet that few [health care providers] ask the question regarding decisions to drive," says Clarke. "My personal experience has been that few patients, at least the ones I know, ever check their BGs before driving."

Symptoms of low blood sugar may include loss of judgment, shakiness, trembling, sweating, pounding heart, irritability, inability to think clearly, visual disturbance and lack of coordination.