Management> Social/Legal>

DEFINITION

• The vast majority of people with diabetes drive regularly and safely.
• Driving by patients with diabetes may, however, be impaired by three factors: hypoglycemia, diabetes complications, and hyperglycemia.
• Hypoglycemia unawareness may pose an increased threat to driving.

EPIDEMIOLOGY

• Only 0.4 - 3% of fatal motor vehicle accidents (MVAs) directly caused by medical conditions (Grattan). Epilepsy most common medical condition (38%), followed by insulin-treated diabetes (18%) and acute myocardial infarction (8%); no cause in 21%.
• MVA rates are variably reported as being similar, higher or lower among persons with insulin-treated diabetes compared to their counterparts (Cox; Mathieson).
• Among U.S. persons with type 1 diabetes, 31% admitted to driving in hypoglycemic stupor during past 2 years; 28% experienced hypoglycemia while driving during past 6 months. In persons with type 2 diabetes, figures were lower (8% and 6% respectively) (Cox).
• Hypoglycemia unawareness may lead to undetected hypoglycemia while driving and affects approximately 25% of patients with type 1 diabetes; incidence in type 2 diabetes is lower (Johnson; Zammit). Even a single episode of hypoglycemia may lead to hypoglycemia unawareness (Veneman).
• Among drivers with diabetes, insulin-treated diabetes and diabetes duration > 5 years both associated with higher injury risk (Kopesell).
• Hospital admission rates of drivers with insulin-treated diabetes versus those without diabetes is slightly increased (de Klerk; Kennedy).
• In survey of 68,770 drivers by National Highway Traffic Safety Administration, drivers with diabetes (and other metabolic conditions) and an unrestricted driving license had 1.44 times higher risk of at-fault accidents.
• Retinopathy associated with decreased vision; treatment with laser coagulation may also reduce peripheral vision (Pearson). Peripheral neuropathy may interfere with operation of vehicle.
• Cognitive dysfunction may interfere with driving ability; associated with acute and possibly chronic hyperglycemia (Cox), tight glycemic control and acute hypoglycemia.
• Older drivers may represent a subset of individuals at higher risk for MVAs (McCoy), but older women with diabetes are more likely to give up driving than older women without diabetes (Forrest).

SIGNS AND SYMPTOMS

• Driving associated with increased metabolic demand in persons with diabetes, manifesting as: increased heart rate, more autonomic symptoms, and trend towards greater epinephrine release (Cox).

CLINICAL TREATMENT

• Persons with type 1 diabetes may not correctly judge when their blood glucose is too low; in one study, subjects stated they would drive 38 - 47% of the time when their actual blood glucose was <40 mg/dl (2.2 mmol/l) (Clarke).
• Hypoglycemia unawareness associated with increased likelihood of driving while hypoglycemic (Stork)
• Hypoglycemia induced by hyperinsulinemic clamp in persons with type 1 diabetes during driving simulation studies to examine effects on performance (Cox)
• Moderate hypoglycemia <50 mg/dl (2.6 mmol/l) associated with reduced driving performance (swerving, spinning, time over midline, time off the road) and more compensatory slow driving; only 50% of patients said they would not drive under similar conditions in real life.
• When subjects given opportunity to self-treat symptoms of hypoglycemia or discontinue driving in simulation studies, only 32% of patients took corrective action although 79% detected moderate hypoglycemia.
• However, real life driving conditions more complex and control group not included in these studies.
• Blood glucose awareness training programs developed to teach patients to more accurately estimate blood glucose levels; MVA rates significantly lower in educated versus uneducated persons with diabetes (Cox; Broers).

• Always keep carbohydrate in vehicle
• Self-monitoring of blood glucose equipment (i.e., glucometer) should be available in vehicle.
• Consider testing blood glucose before driving, especially in patients with hypoglycemia unawareness.
• Stop driving at the very first symptom of possible hypoglycemia and do not resume driving until blood glucose is proven to be in safe range.
• Patient education to emphasize potential deterioration in driving performance when blood glucose <70 mg/dl (4 mmol/l)
• Licensing authority and motor insurance company should be informed if hypoglycemia while driving occurs; patient compliance with statutory requirements generally good (Graveling)

• Current legal restrictions regarding diabetes and driving privileges vary widely; most laws are prompted by potential risks of hypoglycemia though some may, unfortunately, be prompted by a limited understanding of diabetes and its complications.
• Laws should balance individual interests of patient with general traffic safety.
• In U.S., many states have restrictive licensing programs for persons with diabetes.
• In California, mandatory for doctors to report unexpected loss of consciousness from hypoglycemia, usually resulting in revocation of driver's license
• In most other states, such reporting voluntary
• Insulin-treated individuals automatically denied an interstate commercial driving license with few exceptions; however, waivers have been granted in 39 out of 50 states in last decade (Stork)
• In Europe, restrictions range from more frequent medical examinations to denial of driving privileges for people with diabetes.

EXPERT COMMENTS

• MVAs directly caused by diabetes are rare.
• There are many people with diabetes who can and do drive safely, but some who cannot.
• Lack of severe hypoglycemia (change in mental status) for the previous 3 years, and lack of hypoglycemia unawareness indicate good chance of driving safely.
• Hypoglycemia during driving does occur, however, especially in persons with insulin-treated diabetes, causing what is probably a slightly increased risk of MVAs.
• Risk factors for MVA probably include: recent severe hypoglycemia (mental status change), hypoglycemia unawareness, older age (with more rapid decline in cognitive function).
• Our recommendation is that each person be considered and evaluated individually, rather than setting blanket policies that unfairly discriminate against people with diabetes.
• Further research still needed to better describe association between diabetes and MVAs.

Basis for Recommendations

• Stork AD, van Haeften TW, Veneman TF; Diabetes and driving: Desired data, research methods and their pitfalls, current knowledge, and future research.; Diabetes Care; 2006; Vol. 29; pp. 1942-9;
  ISSN: 0149-5992;
  PUBMED: 16873810
  Rating: Basis for recommendation
  Comments:Most up-to-date review on the current knowledge regarding diabetes and driving, along with recommendations for future research directions.
  
  

REFERENCES