What do Doctors Need to Teach Their Patients with Diabetes about Driving Their Vehicles?
Q. How often do clinicians counsel patients with diabetes regarding driving safety issues?
A. In a recent survey of patients with diabetes, 50% of those diagnosed with type 1 diabetes (T1D) and 75% of those with type 2 diabetes (T2D) remembered their physicians counseling them on the effects of hypoglycemia and driving.1 In a survey of healthcare professionals, more than one-third did not recommend that insulin-treated diabetics test their glucose levels before driving and 13% felt it was safe for diabetics to drive with a glucose level <4 mmol/L (72 mg/dL).2
Q. How frequently do driving mishaps occur and are they more prevalent in persons with T1D versus T2D?
A. A 2-year, multinational study revealed that those with T1D were involved in a substantially greater number of motor vehicle crashes (19%) than those with T2D (12%) or spouses of diabetics (8%).1 However, the incidence of crashes involving those with T1D is less than half the risk of drivers with attention-deficit hyperactivity disorder, obstructive sleep apnea, and alcohol abuse.1
Q. Other than motor vehicle crashes, what other types of mishaps occur among persons with T1D?
A. In the previously cited study,1 moving violations occurred in 15% T1D, 8% T2D, and 10% spouses of diabetics. T1Ds were also more likely to experience mild hypoglycemia or stupor, and require assistance while driving. A follow-up study of T1Ds revealed that, during a 12-month period, 52% of T1Ds reported at least 1 hypoglycemia-related driving mishap, 32% reported 2 or more, and 5% reported 6 or more events.3
Q. What are risk factors for driving mishaps among persons with T1D?
A. Major risk factors include failure to check glucose levels within 30 minutes of driving, ignoring low glucose levels, prior episodes of mild hypoglycemia while driving, and previous hypoglycemia-related mishaps.1,3
Physiologically, about 25% of persons with T1D experience hypoglycemia unawareness. Diabetic retinopathy can result in impaired vision while diabetic neuropathy may affect the mechanical operation of a vehicle.2,4 Associated sleep apnea may pose an additional risk.2
In 2003, a study found that insulin pump therapy did not increase events.1 However, in a follow-up study 6 years later, the same authors found a 35% higher incidence of events in diabetics receiving insulin pump therapy.3
Duration of diabetes, gender, extreme hyperglycemia, HA1c level, or intensity of insulin therapy (≤2 vs >2 insulin injections a day) have no significant effect on the incidence of driving mishaps.2 Although persons younger than 25 or older than 60 years are more likely to be involved in vehicle crashes or commit moving violations, age was not determined to be an independent risk factor in T1D.1,4
Q. What may be done to reduce the incidence of driving mishaps among persons with T1D?
A. Physicians should review blood glucose logs, ask about hypoglycemic episodes, and make certain that T1Ds are receiving regular eye examinations. In some cases, initiation of continuous blood glucose monitoring can also be beneficial. Blood glucose awareness training significantly reduces accident rates, although some T1Ds are reluctant to forego driving when their glucose levels are low.2,4
Physicians should recommend that T1Ds check their glucose levels within 30 to 90 minutes before driving, carry fast-acting carbohydrate snacks in the car, and measure glucose levels more frequently (eg, hourly) on long trips.1,2 Persons with diabetes should not drive when blood glucose is <5 mmol/L (80 mg/dL) and they should park and check their glucose levels when they experience signs of even minor hypoglycemia. For those using continuous glucose monitoring, the levels should be confirmed by standard blood glucose testing.2
Q. What regulations exist regarding diabetes and driving?
A. The National Highway Traffic Safety Association has set forth guidelines regarding diabetes and safe driving,5 but individual state regulations vary. In general, hypoglycemia unawareness, hypoglycemic episodes requiring third-party assistance, and a history of driving mishaps may be incompatible with safe driving. It is important to note that insulin treatment alone does not disqualify T1Ds from driving.
There are separate regulations for insulin-treated diabetics who operate commercial motor vehicles.6 In order to maintain their licenses, these drivers must demonstrate responsibility in self-testing glucoses, document driving without hypoglycemia, and receive certification from a diabetes specialist.
Physicians must use their professional judgment to determine if a patient is an at-risk driver and whether this information should be reported to licensing agencies for a review of driving privileges.2 However, this could have a negative effect on the doctor–patient relationship and discourage patients from open communication. There is no evidence that such reports affect the crash rate or benefit public safety.
Q. What resources exist regarding diabetes and driving?
A. The following links may be useful for clinicians:
• American Diabetes Association: Driving Safety http://www.diabetes.org/living-with-diabetes/know-your-rights/discrimination/drivers-licenses/driving-safety.html
• American Diabetes Association: Driver License Laws by State http://www.diabetes.org/living-with-diabetes/know-your-rights/discrimination/drivers-licenses/drivers-license-laws-by-state.html
• National Highway Traffic Safety Administration http://www.nhtsa.gov/people/injury/olddrive/diabetes%20web/ ■
Kim A. Carmichael, MD, is an associate professor of medicine, Department of Internal Medicine, Division of Endocrinology, Diabetes, and Lipid research at Washington University School of Medicine in St Louis, MO.
1.Cox DJ, Penberthy JK, Srebic J, et al. Diabetes and driving mishaps. Diabetes Care. 2003;26:2329-2334.
2.American Diabetes Association. Diabetes and driving. Diabetes Care. 2013;36 (Suppl 1):S80-S85.
3.Cox DJ, Ford D, Gonder-Frederick L, et al. Driving mishaps among individuals with type 1 diabetes. Diabetes Care. 2009;32:
4.Stork ADM, van Haeften TW, Veneman TF. Diabetes and driving. Diabetes Care. 2006;29(8):1942-1949.
5.National Highway Traffic Safety Association. Driver Fitness Medical Guidelines 2009. Available at: http://www.nhtsa.gov/DOT/NHTSA/Traffic%20Injury%20Control/Articles/Associated%20Files/811210.pdf. Accessed March 2014.
6.US Department of Transportation. Qualification of Drivers; Exemption Applications; Diabetes. Federal Register. 2003;68:
170(68 FR 52441).