A diagnosis of diabetes mellitus does not disqualify a person from driving, but symptoms such as peripheral neuropathy and retinopathy, as well as treatment consequences such as hypoglycemia, can increase the risk of driving impairment, said Dr. Daniel Lorber, a specialist in diabetes and the law.
Dr. Daniel L. Lorber
The ADA recommends that when considering the fitness for driving of a patient with diabetes controlled with insulin, the physician should evaluate patients’ hypoglycemia history and risk, ability to detect early hypoglycemia, their ability to self-monitor blood glucose and manage their disease, and whether they have diabetes-related complications that may impair their ability to drive safely, Dr. Lorber, director of endocrinology at New York Hospital, Queens, said at the annual advanced postgraduate course held by the American Diabetes Association.
"There really is a whole variety of variables in diabetes, not merely aging, and not merely hypoglycemia, that affect how people drive, but we do know that moderate hypoglycemia does impair driving safety," said Dr. Lorber, who also serves on the ADA’s legal advocacy subcommittee.
"You can’t make driving safe. Frankly, you can’t make crossing the street safe; you can just make diabetic driving less dangerous," he said.
Fifty-one licensing authorities
There is great variability among patients with diabetes, he noted, and decisions about driving ability have to be made on a case-by-case basis. The clinician’s task is made harder by the jumble of state licensing authorities (51, including the District of Columbia), and, for commercial drivers, federal licensing regulations from the U.S. Department of Transportation and the Federal Motor Carrier Safety Administration (FMCSA).
Regulations vary from one state to the next, but most require evaluation of patients with diabetes following a motor vehicle accident, and a few states, such as Pennsylvania, have specific referral requirements to the department of motor vehicles after a severe hypoglycemic event, with or without a motor vehicle. State mandatory reporting laws may put physicians who care for diabetes patients in a bind, caught between state requirements and the Health Insurance Portability and Accountability Act of 1996 (HIPAA) privacy mandates, Dr. Lorber said.
For commercial drivers who engage in interstate commerce, the federal government bans commercial licensure of people with insulin-treated diabetes, except those who meet stringent requirements that include being on insulin for a minimum of 1-2 months, no severe hypoglycemia in the past 12 months and no more than two severe episodes over the preceding 5 years, and no unstable retinopathy or other disqualifying condition. Additionally, commercial drivers must demonstrate diabetes education and willingness to manage their condition, maintain a driving and blood glucose log, check their blood sugars every 2-4 hours and only drive if their levels are between 100 and 400 mg/dL, submit quarterly and annual reports to the U.S. Department of Transportation, and report all motor vehicle accidents and adverse driving events.
A systematic review of the data on diabetes and driving risk prepared for the FMCSA had equivocal results, finding on the one hand that there was no evidence for a higher risk of crashes among people on insulin, but on the other hand that "hypoglycemia has a significant deleterious effect on the driving ability of some individuals with type 1 DM when measured using a driving simulator."
The review authors noted that in three small studies, there was a suggestion of a deleterious relationship between hypoglycemia and simulated driving tasks, but they saw no consistent pattern of impairment or the sensitivity of task impairments associated with specific levels of hypoglycemia.
Relatively low risk
Based on data from the systematic review, Dr. Lorber estimated the relative risk for motor vehicle accidents in persons with any type of diabetes to be 1.12 to 1.19 times higher than that of controls, and for patients with type 1 DM and a history of severe hypoglycemia within the prior 2 years: 1.5 to 2 times higher.
Both compare favorably to the accident risk for 16-year-old males compared with 35- to 45-year-old females (42-fold), rural vs. urban highways (9.2-fold more accidents on rural highways), and 1 a.m. Sunday vs. 11 a.m. Sunday (142 times higher at 1 am).
Dr. Lorber also pointed out that nondiabetic drivers are also exposed to risks from sedating over-the-counter medications sold in convenience stores and gas station mini marts, such as diphenhydramine (Benadryl)-containing products, Tylenol Allergy (acetaminophen with chlorpheniramine), or NyQuil, a cold medicine that contains the antihistamine doxylamine.
To make driving safer for those at risk for hypoglycemia, he recommends measuring blood glucose before driving and never driving with values from 70 to 90 mg/dL without first having prophylactic carbohydrates, never driving with a blood glucose below 70 mg/dL, and treating prophylactically during long drives,