Section 19

Endocrine and metabolic disorders

Disturbances in the functioning of the endocrine glands may be the source of many symptoms with a wide range of severity. Patients with suspected or confirmed endocrine disorders should always be carefully evaluated to make certain that their symptoms do not make them unsafe drivers. The endocrine and metabolic conditions discussed below are among the most common ones that physicians may be called upon to assess because of their potential for interfering with driving safety. Fitness to drive must be assessed on a case-by-case basis, as the range of signs and symptoms is highly variable.

Advances in treatment, medical technology, and self-monitoring have increased the ability of patients with diabetes to control their disease and operate a motor vehicle safely. Fitness of these patients to drive must be assessed on a case-by-case basis. Patients with diabetes should be encouraged to take an active role in assessing their ability to drive by maintaining personal health records and accurate blood glucose monitoring logs. Patients should have information concerning avoidance and recognition of, and appropriate therapeutic intervention for, hypoglycemia.

The annual medical examination of a driver with diabetes should always include a full review of possible complications, to exclude eye disease, renal disease, neuropathy (autonomic, sensory, motor), cardiovascular disease, and cerebrovascular disease of a degree that would preclude issuing the class of licence requested. Cumulative diabetic complications may cause functional impairment requiring evaluation beyond what might be required for any specific level of complication or level of glycemic control. In general, patients are considered fit to drive if it can be demonstrated that they (1) are fastidious and knowledgeable about controlling their blood glucose levels, (2) are able to avoid severe hypoglycemic episodes, and (3) have no complications of diabetes that would affect safe driving.

For recommendations and additional information pertaining to drivers with diabetes who are receiving treatment appropriate to their situation, please review the 2018 Diabetes Canada guidelines on diabetes and driving (Houlden et al., 2018). The recommendations (all Grade D, Consensus, except where indicated otherwise) are as follows:

1. Fitness of people with diabetes to drive should be assessed on an individual basis. People with diabetes should take an active role in assessing their ability to drive safely.
2. All drivers with diabetes should undergo a comprehensive medical examination at least every 2 years by a physician/nurse practitioner competent in managing people with diabetes. The medical examination should include an assessment of glycemic control; frequency and severity of hypoglycemia; symptomatic awareness of hypoglycemia; and the presence of retinopathy, neuropathy, nephropathy, amputation and CV [cardiovascular] disease, to identify whether any of these factors could significantly increase the risk of a motor vehicle accident. Commercial drivers should also undergo a medical examination at the time of application for a commercial license.
3. Drivers with diabetes treated with insulin secretagogues and/or insulin:
   1. Should maintain a log of their SMBG [self-monitored blood glucose] measurements either by using a memory- equipped BG [blood glucose] meter or electronic record of BG measurement performed at a frequency deemed appropriate by the person with diabetes and their health-care team. For commercial drivers, for initial commercial licence application, the record should include the last 6 months (or since the diagnosis of diabetes if less than 6 months). BG logs should be verifiable on request.
   2. Should always have BG monitoring equipment and supplies of rapidly absorbed carbohydrate within easy reach (e.g. attached to the driver’s-side visor or in the centre console).
   3. Should consider measuring their BG level immediately before and at least every 4 hours while driving or wear a real-time CGM [continuous glucose monitoring] device.
   4. Should not drive when their BG level is <4.0 mmol/L [Grade C, Level 3 for type 1 diabetes; Grade D, Consensus for type 2 diabetes]. If the BG level is <4.0 mmol/L, they should not drive until at least 40 minutes after successful treatment of hypoglycemia has increased their BG level to at least 5.0 mmol/L [Grade C, Level 3 for type 1 diabetes; Grade D, Consensus for type 2 diabetes].
   5. Must refrain from driving immediately if they experience severe hypoglycemia while driving, and notify their health-care provider as soon as possible (no longer than 72 hours).
4. Private [non-commercial] and commercial drivers with diabetes and hypoglycemia unawareness or history of severe hypoglycemia in the past 12 months must measure their BG level immediately before and at least every 2 hours while driving or wear a real-time CGM device.
5. If any of the following occur, health-care professionals should inform people with diabetes treated with insulin secretagogues and/or insulin to no longer drive, and should report their concerns about the person’s fitness to drive to the appropriate driving licensing body:
   1. Any episode of severe hypoglycemia while driving in the past 12 months.
   2. More than 1 episode of severe hypoglycemia while awake but not driving in the past 6 months for private [non- commercial] drivers, and in the past 12 months for commercial drivers.

The full guideline can be accessed online at https://www.diabetes.ca/health-care-providers/clinical-practice-guidelines/chapter-21#panel-tab_FullText

For commercial drivers who have had their licence suspended, all Canadian jurisdictions allow for shorter periods of suspension of driving privileges following an episode of hypoglycemia that required the intervention of a third person, if recommended by a specialist. Circumstances that could merit a shorter period of suspension include the following:

• Reinstatement of a commercial licence may be considered for persons with diabetes treated with insulin secretagogues whose commercial licence has been suspended owing to severe hypoglycemia or hypoglycemia unawareness if in the past 6 months there have been no episodes of severe hypoglycemia and no evidence of hypoglycemia unawareness.
• Drivers with diabetes who are taking insulin should be excluded from obtaining or maintaining a commercial licence if in the past 6 months they have had any episode of severe hypoglycemia while awake or any hypoglycemia unawareness.
• Reinstatement of a commercial licence may be considered for persons with diabetes treated with insulin whose commercial licence has been suspended owing to severe hypoglycemia or hypoglycemia unawareness if in the past 6 months there are no episodes of severe hypoglycemia and no evidence of hypoglycemia unawareness.

Provincial guidelines may differ from the above, and reinstatement of a commercial licence may be prolonged or shortened on a case-by-case basis, depending on perceived risk for driver safety.

Similar recommendations apply to non-commercial drivers who are subject to shorter periods without driving. If the specialist is satisfied that the situation that caused the suspension of driving privileges has been resolved and the patient’s condition has been stabilized for a sufficient period, a recommendation to the licensing agency may be justified.

Patients with nondiabetic renal glycosuria can safely drive any type of motor vehicle.

Patients who become faint or unconscious from spontaneous episodes of hypoglycemia that is unrelated to diabetes cannot drive any type of vehicle safely and require immediate, accurate diagnosis and treatment of the condition. Those with milder symptoms, who have never lost consciousness or the ability to respond normally to external stimuli, can operate non-commercial vehicles without excessive risk. They should not drive passenger-carrying or commercial vehicles until this problem has been controlled.

Patients with hyperthyroidism complicated by significant visual, cardiac, neurologic, or muscular symptoms and patients with symptomatic hypothyroidism that impairs judgment or motor skills should not drive any type of motor vehicle until the condition has been controlled.

Patients with severe hypercalcemia or hypocalcemia with significant neurologic symptoms, cardiac conduction abnormalities, or muscular symptoms should not drive. If their symptoms respond well to treatment, they should be able to resume driving all vehicles without undue risk.