4. Diabetes
This section covers:
- Summary table
- Introduction
- 4.1 Type 1 diabetes
- 4.2 Type 2 diabetes controlled by diet alone
- 4.3 Type 2 diabetes controlled by oral hypoglycaemic agents
- 4.4 Type 2 diabetes partly or solely controlled by insulin
Summary table
The table below summarises the information outlined in this section. However, practitioners should ensure that they are familiar with the guidance outlined in the entire section rather than relying solely on the table.
The recommended minimum stand-down periods from driving and guidelines only apply where an individual's medical condition has been adequately treated and stability has been achieved so that road safety is unlikely to be compromised.
| Diabetic type and treatment type | Class 1 or class 6 licence and/or a D, F, R, T or W endorsement (see appendix 3) | Class 2, 3, 4 or 5 licence and/or a P, V, I or O endorsement |
|---|---|---|
| Type 2 diabetes with dietary control only | Generally considered fit to drive. | Same as private classes. |
| Type 2 diabetes controlled by oral hypoglycaemic agents | Generally considered fit to drive. | Generally considered fit to drive but may have licence conditions. |
| Type 2 diabetes requiring insulin supplementation | Generally considered fit to drive. | Some, but not all, individuals may be considered fit to drive and are likely to have licence conditions. Specialist assessment is necessary. |
| Type 1 diabetes | Generally considered fit to drive. | Generally considered unfit to drive 4 |
| Individuals with severe hypoglycaemia unawareness | Should not drive until successfully managed and a satisfactory period of observation has passed without any further episodes. | Generally considered unfit to drive. |
4 The Agency may grant a licence in exceptional circumstances, subject to strict licence conditions being imposed, and a favourable assessment by a specialist.
Factors for medical practitioners to consider
The aim of determining fitness to drive is to minimise the risk to the individual, and other road users, while maintaining appropriate independence and employment. Medical practitioners should consider the following factors, in addition to the guidance outlined in this chapter, when assessing an individual for fitness to drive:
- Type of licence held and type of driving undertaken - professional drivers spend up to an entire working week in their vehicle, and that vehicle can weigh greater than 25,000kg or carry many passengers. A crash involving such a vehicle could put many people at risk. Some forms of commercial driving could exacerbate risks of hypoglycaemic attacks more than others
- Timing, shifts and total driving hours - hypoglycaemia on sulphonylurea drugs and insulin is most common before meals, especially pre-lunch, and is also common overnight. Shift work is more of a risk than regular hours, and total driving hours should not be excessive
- Medication - consider the effects of medications, and likely compliance with medications, on the individual's ability to drive safely
- Presence of any complications of the disease - particularly any possible visual impairments
- Individual's motor vehicle crash history (if known) - medical practitioners may need to recommend a longer period of refraining from driving if an individual has a history or pattern of crashes that may be associated with their condition. Where a medical practitioner is aware of a medically related crash, they must inform the Agency if the individual's medical condition remains unresolved and the individual is likely to continue to drive (refer to section 1.4 )
- Presence of multiple medical conditions - where an individual has multiple medical conditions, consider any possible combined effects on their ability to drive safely
- Alcohol abuse - a possible alcohol-abuse problem may increase the likelihood of hypoglycaemic attacks.
Dealing with individuals who are unfit to drive
Medical practitioners can usually successfully negotiate short-term cessation of driving.
A person deemed unfit to drive because of severe or recurrent hypoglycaemia or with hypoglycaemia unawareness should be informed of this by their medical practitioner. Written notification should also be given. The individual should be told how soon they might expect to have this situation reviewed. If a practitioner suspects that the individual is continuing to drive against medical advice, they are legally obliged to inform the Agency under section 18 of the Land Transport Act 1998 (see section 1.4 ).
Introduction
Diabetes is a common condition in New Zealand. Current estimates suggest that at least 100,000 people are being treated for the condition and many more are as yet undiagnosed (Ministry of Health 2008). The number of road traffic crashes attributable to diabetes or its treatment is not known, but it is likely to be relatively small. Monitoring by the Agency suggests that diabetes accounts for about 5-10 percent of those motor vehicle crashes attributable to medical factors.
The potential risks of diabetes derive from the metabolic disturbances associated with control of blood glucose on the one hand, and the later complications of the disease on the other. The later complications, giving rise to end-organ damage, should be assessed separately using advice from the appropriate sections of this guide. Specifically, these include:
- visual acuity problems arising from cataract formation and/or diabetic retinopathy and its treatment (see section 6 ) (note that subjects who have had extensive laser photocoagulation of the retinae often have very poor vision at night, despite adequate daytime acuity, and may also have a limited visual field)
- ischaemic heart disease and cerebrovascular disease, both of which are more prevalent in people with diabetes (see section 3 and section 2 , respectively)
- locomotor conditions, particularly of the lower limbs, arising from peripheral neuropathy and/or peripheral vascular disease (see section 5 ).
- Note: obstructive sleep apnoea is not uncommon in obese subjects with type 2 diabetes (see section 10 ).
Hyperglycaemia and associated diabetic coma (whether ketotic or nonketotic) are generally of little significance to driver safety, as the onset is slow. Hypoglycaemia induced by treatment of diabetes is undoubtedly the most important potential problem from the point of view of driving safety. Its onset may rapidly impair the ability of an otherwise competent and safe driver. It may result in poor motor coordination, impaired judgement and reaction times, inappropriate and aggressive behaviour, and even loss of consciousness. These all pose a potential risk on the roads. The risk of hypoglycaemia is not the same in all patients with diabetes, and the forms of treatment associated with different types of the disease are given different weightings in the guidelines that follow.
The risks of hypoglycaemia are greater with increased driving hours, and the consequences of a crash are potentially greater with larger vehicles and those carrying passengers. Higher safety standards (lower risks) are therefore required for these classes and endorsements.
Hypoglycaemia – causes
Hypoglycaemia is a side effect of treatment of diabetes with insulin or sulphonylurea drugs and also with some newer drugs not currently available in New Zealand. The risk of hypoglycaemia with sulphonylurea drugs is greatest in the elderly, and in subjects with weight loss and poor renal function. It is most likely to occur with long-acting agents, such as glibenclamide. In insulin users, hypoglycaemia usually arises through missed meals, inaccurate or inappropriate insulin dosing, and during or following exercise. It is common in those attempting or achieving tight glycaemic control. With either sulphonylurea drugs or insulin, hypoglycaemia can also occur with alcohol consumption.
Hypoglycaemia unawareness
An inability to detect developing hypoglycaemia and to respond to it appropriately in good time is the single greatest hazard for diabetic drivers. The risk of crashing may be increased 20-fold in this group (Lave et al 1993). As with alcohol intoxication, individuals with this problem may significantly underestimate the degree to which their driving is impaired. The major risk factors for hypoglycaemia unawareness are:
- a prior history of severe hypoglycaemia
- intensive hypoglycaemic therapy
- type 1 diabetes of long duration.
In this context, severe hypoglycaemia is defined as that requiring the help of another party to manage it. Important questions for practitioners to ask in the detection of hypoglycaemia unawareness are:
- Have you recently experienced severe hypoglycaemia? How many episodes have there been in the last 12 months? Daytime and night-time (waking from sleep) episodes should be documented separately.
- What symptoms tell you that your blood glucose is getting low? Individuals who report sweating, shaking, tremor and palpitations as their early warning symptoms are likely to have adequate awareness. Those who report confusion, slurred speech, unsteadiness, difficulty concentrating and sleepiness are likely to have impaired awareness.
- Are you usually able to detect hypoglycaemia before your partner (or friends, family or colleagues)? Or are they usually the first to realise that you are ‘hypo’ and draw your attention to it? The latter suggests unawareness.
Corroboration by a partner, family member, friend or colleague strengthens the conclusions that can be drawn from the individual's answer. Inspection of the individual's home blood glucose recordings is important. Individuals with hypoglycaemia unawareness often have levels of 3mmol/l or less without symptoms. Those with more than 5 5
10 percent of readings below 4mmol/l are also likely to be at risk. HbA1c measurements are often close to, or in, the normal range in such individuals.
Hypoglycaemia unawareness is an indication for specialist referral. It can be difficult to manage successfully. The basis of management involves some relaxation of glycaemic targets, intensive self blood glucose monitoring to detect periods of unrecognised hypoglycaemia (particularly at night) and the modification of meals and the insulin regimen.
Individuals with very marked hypoglycaemia unawareness, usually those with type 1 diabetes, should not drive until this can be successfully managed, if possible. If hypoglycaemia unawareness has been successfully managed, an appropriate observation period free of episodes should be required before allowing a return to driving. A specialist assessment should be undertaken before a return to driving.
Management of hypoglycaemia
People taking either insulin or sulphonylurea drugs should be made aware of the precautions they should take to avoid hypoglycaemia while driving, and to manage it should it occur. Adequate education, by an experienced diabetes nurse educator, is strongly recommended for these individuals. These precautions, which apply to all such individuals whatever their class of licence/endorsement, include:
- regular testing and recording of blood glucose, especially before driving
- testing blood glucose every couple of hours on long journeys
- always carrying a form of rapidly absorbed glucose within easy reach in the vehicle
- always having a meal or snack before undertaking long journeys
- telling co-travellers that the individual has diabetes.
The action to be taken if hypoglycaemia occurs while driving includes:
- stop the car and eat fast-acting sugary food
- eat a meal of longer-lasting carbohydrate as soon as possible
- wait until recovery is complete before resuming the journey.
Alcohol
Alcohol use is particularly hazardous for drivers with diabetes. As well as impairing driving performance in its own right, alcohol can precipitate hypoglycaemia (if food intake is inadequate) and it increases hypoglycaemia unawareness.
Temporary unfitness to drive
Following mild hypoglycaemia, individuals should not drive for at least an hour, as full cognition can take this long to recover. Following an episode of severe hypoglycaemia, patients should not drive for 24 hours.
An individual who experiences a severe hypoglycaemic episode while driving, irrespective of whether a crash occurred or not, should be advised to stop driving. A minimum period of a month is recommended, during which time remedial action needs to be undertaken. Specialist review will almost certainly be required. Hypoglycaemia in sulphonylurea users can be prolonged, and driving should be stopped for at least 48 hours. Individuals having major changes in therapy (particularly starting insulin treatment) can be temporarily unfit to drive, and may need to stop driving for a few days until it is clear that hypoglycaemia is not a difficulty.
Individuals who have had their pupils dilated for the purpose of retinal examination are also advised not to drive for two hours.
4.1 Type 1 diabetes
Individuals in this group are most likely to suffer hypoglycaemia, and are also those whose diabetes is most difficult to control. Individuals with unstable diabetes should be reviewed thoroughly before being given permission to drive, and adequate education should be given. Practitioners should be aware of the particular dangers of hypoglycaemia in the period after starting insulin therapy, or following major treatment readjustments. Individuals may be temporarily unfit to drive at such times.
Medical standards for individuals applying for or renewing a class 1 or class 6 licence and/or a D, F, R, T or W endorsement
- See appendix 3
There are generally no private driving restrictions for individuals with type 1 diabetes who are on insulin. However, the medical practitioner should seek to ensure that these individuals are adhering to their medication regimes, regularly performing blood glucose self-monitoring and maintaining a reasonable level of glycaemic control while minimising the number of hypoglycaemic episodes. It is important that these individuals are regularly monitored, with particular attention to the emergence of diabetic complications that can also affect fitness to drive. Individuals should be aware of the risks of hypoglycaemia and the danger of drinking alcohol.
Medical standards for individuals applying for or renewing a class 2, 3, 4 or 5 licence and/or a P, V, I or O endorsement
When driving should cease
People with type 1 diabetes are generally not considered fit to drive.
When driving may resume or occur
The Agency may, in exceptional circumstances, grant a licence after consultation with the individual's general practitioner and diabetes specialist. Strict conditions are likely to be imposed, which would include the requirements listed below in section 4.4 .
4.2 Type 2 diabetes controlled by diet alone
The risks of hypoglycaemia may effectively be discounted in this group, and these individuals may be considered fit for all types of driver licence. However, a change in the requirements for effective glycaemic control (eg the introduction of sulphonylurea drugs or insulin) may necessitate the imposition of restrictions. Late complications of diabetes do occur in such individuals.
4.3 Type 2 diabetes controlled by oral hypoglycaemic agents
The risk of hypoglycaemia is relatively low, but it can occur with the sulphonylurea drugs (tolbutamide, gliclazide, glipizide, glibenclamide) and with meglitinide drugs. It is important that food is not omitted when these tablets are being taken. Individuals should be aware of the risks of hypoglycaemia and the danger of drinking alcohol. Metformin when taken without insulin or sulphonylurea drugs does not cause hypoglycaemia. The same applies to drugs of the thiazolidenedione group and acarbose. It is important that these individuals are regularly monitored for the emergence of diabetic complications that can affect fitness to drive.
Medical standards for individuals applying for or renewing a class 1 or class 6 licence and/or a D, F, R, T or W endorsement
- See appendix 3
No restrictions apply to private driving, but the addition of insulin to achieve better glycaemic control may lead to a period of temporary unfitness to drive.
Medical standards for individuals applying for or renewing a class 2, 3, 4 or 5 licence and/or a P, V, I or O endorsement
These drivers may be considered fit to drive in most circumstances on a licence with conditions, provided there is no history of hypoglycaemia. An initial review from a diabetes specialist may be required to ensure that the treatment regimen is satisfactory, adequate glycaemic control is being achieved and there are no complications of diabetes that may impair driving performance. The granting of a licence in these categories is likely to require the following conditions:
- an annual medical certificate from a GP documenting:
- adherence to treatment
- that the medical practitioner has proof of regular self-testing of blood glucose with satisfactory blood glucose levels
- the absence of hypoglycaemic episodes or unawareness
- the absence of significant diabetic complications
- a regular pattern of shifts with adequate meal breaks
- a satisfactory two-yearly specialist assessment.
If the addition of insulin is required to achieve better glycaemic control, then the individual should be considered under section 4.4 .
4.4 Type 2 diabetes partly or solely controlled by insulin
Medical standards for individuals applying for or renewing a class 1 or class 6 licence and/or a D, F, R, T or W endorsement
- See appendix 3
There are generally no driving restrictions for individuals with type 2 diabetes who are on insulin. However, the medical practitioner should seek to ensure that these individuals are adhering to their medication regimes and maintain a reasonable level of glycaemic control while minimising the number of hypoglycaemic episodes. Individuals should be aware of the risks of hypoglycaemia and the danger of drinking alcohol. It is important that these individuals are regularly monitored, with particular attention to the emergence of diabetic complications that can affect fitness to drive.
Medical standards for individuals applying for or renewing a class 2, 3, 4 or 5 licence and/or a P, V, I or O endorsement
In cases where insulin has been added to the treatment, additional conditions will be imposed, and not all individuals will necessarily be considered fit to drive. Nocturnal insulin therapy, when clinically appropriate, carries a lower risk of daytime hypoglycaemia than twice-daily or morning insulin regimens, especially those with short-acting components. A review from a diabetes specialist is necessary to ensure that the treatment regimen is satisfactory, adequate glycaemic control is being achieved and there are no complications of diabetes that may impair driving performance. The granting of a licence in these categories is likely to require the following conditions:
- a six-monthly medical certificate from a GP documenting:
- adherence to treatment
- that the medical practitioner has proof of regular self-testing of blood glucose with satisfactory blood glucose levels
- the absence of hypoglycaemic episodes or unawareness
- the absence of significant diabetic complications.
- a regular pattern of shifts with adequate meal breaks
- a satisfactory annual specialist review.