For people with diabetes who are treated with insulin, the potential risks of hypoglycaemia are always present and have therefore influenced the ways in which modern society regulates and restricts their activities. This principally affects driving licences and some forms of employment. Although most of these restrictions are reasonable and important for public safety, much lay, and even medical, ignorance exists about hypoglycaemia and its effects, so that discriminatory practices still occur, particularly with regard to employment.

Effect of Hypoglycaemia on Driving

Driving is a common and everyday activity that demands complex psychomotor skills, including good visuo-spatial functions, rapid information processing, vigilance and satisfactory judgment. Because hypoglycaemia rapidly interferes with cognitive functions, even modest degrees of neuroglycopenia may affect driving skills, without necessarily provoking symptomatic awareness of hypoglycaemia. Seminal studies using a sophisticated driving simulator have examined the driving abilities of drivers with type 1 diabetes at different blood glucose concentrations, maintained by a glucose clamp (Cox et al., 1993; Cox et al., 2000). Driving performance started to deteriorate when blood glucose declined below 3.8mmol/l, and typical driving deficiencies included speeding and inappropriate braking, driving off the road, crossing the centre line, ignoring 'STOP' signs and causing an increased number of 'crashes'. Allowing for the artificial conditions of a driving simulator, it is evident that hypoglycaemia has an adverse effect on driving performance. A particularly disconcerting observation in these studies was that none of the drivers took action to treat hypoglycaemia until their blood glucose had declined to < 2.8 mmol/l, and then only 30% of the participants responded (Cox et al., 2000). Many of the drivers did not experience any warning symptoms of hypoglycaemia, and fewer than 25% said they did not feel competent to drive when their blood glucose was low (Cox et al., 1993; Cox et al., 2000). The driving simulator studies also demonstrated that driving has a substantial metabolic demand that can lower blood glucose (Cox et al., 2001, Cox et al., 2002), leading the authors to recommend that a prophylactic snack should be consumed before driving if blood glucose is 5.0 mmol/l or less. Various studies have shown that many drivers with insulin-treated diabetes believe that it is safe to drive when their blood glucose is low (Weinger et al., 1999; Clarke et al., 1999; Graveling et al., 2004); this misperception may be influenced by progressive neuroglycopenia.

Hypoglycaemia can impair cognitive function and judgment without necessarily provoking warning symptoms or altering consciousness. Driving can therefore continue while apparently not being under conscious control, a condition which is given the strictly legal term of 'automatism' (there are no medical publications about 'automatism'), and irrational and compulsive behaviour during hypoglycaemia has been described by insulin-treated diabetic drivers (Frier et al., 1980). The police, suspecting alcohol and inebriation to be the cause of a driver's altered behaviour and symptoms, have on occasion arrested diabetic drivers who are hypoglycaemic.

Risk of Accidents and Restriction of Driving Licences

Hypoglycaemia can adversely affect the ability to drive, and in individual cases hypogly-caemia has been implicated as a precipitating cause of road traffic accidents, causing the occasional fatality. In a study of insulin-treated drivers in Northern Ireland, the number of hypoglycaemic episodes that occurred while driving in the preceding year was shown to be associated with the total number of accidents during the previous five years (Stevens et al.,

1989), consistent with Scottish studies which showed a greater rate of accidents among diabetic drivers who experienced hypoglycaemia while driving (Frier et al., 1980; Eadington and Frier, 1989; MacLeod et al., 1993). It is difficult to quantitate how often hypoglycaemia occurs during driving and how often this precipitates a road traffic accident, particularly as hypoglycaemic incidents in which the diabetic driver is killed are seldom identified after the event. In the UK, around a third of insulin-treated diabetic drivers have admitted to experiencing hypoglycaemia while driving (Frier et al., 1980; Stevens et al., 1989; Eadington and Frier, 1989; Graveling et al., 2004).

The rate of hypoglycaemia-induced accidents is extremely difficult to evaluate and is, of necessity, anecdotal. Most road accidents have several contributory factors, and it may be difficult to isolate hypoglycaemia as being the principal cause. Studies in the UK have suggested that the accident rate of diabetic drivers is very similar to non-diabetic drivers (Stevens et al., 1989; Eadington and Frier, 1989), and this premise is supported by studies from Germany (Chantelau et al., 1990) and the USA (Songer et al., 1988) (Table 14.1). In an assessment of medical factors causing road traffic accidents, a study in Iceland showed that disorders such as diabetes were not over-represented (Gislason et al., 1997). However, one American study has observed a 'slight increase' in the risk of motor vehicle accidents in diabetic drivers (Hansotia and Broste, 1991), but considered this increase to be insufficient to 'warrant further restrictions on driving privileges'. These studies have been criticised for being retrospective, for excluding fatal accidents and being influenced by the removal of diabetic drivers who have ceased driving either by their own volition or through the efforts of the regulatory authorities. Police notifications in the UK to the Driver and Vehicle Licensing Agency (DVLA) of serious accidents associated with hypoglycaemia have risen steadily in recent years, which probably represent an increase in identification and reporting, rather than an increasing risk of hypoglycaemia-related road traffic accidents, but several fatalities associated with hypoglycaemic drivers are reported annually. Most licensing authorities in states in the European Community issue ordinary driving licences to people with insulin-treated diabetes that are restricted in duration, and are subject to medical review. Other than visual impairment, the principal factors that commonly lead to an ordinary driving licence being revoked are related to hypoglycaemia. Impaired awareness of hypoglycaemia with its increased risk of severe hypoglycaemia (see Chapter 7), and recurrent severe hypoglycaemia during waking hours clearly present hazards to safe driving by diminishing medical fitness to drive and are common reasons for driving licences being revoked.

Table 14.1 Hypoglycaemia-related road traffic accidents: rates per mileage driven


Time (years)

Hypo-related accidents

Total mileage (X 106)

Hypo-related accidents per 106 miles

Eadington and Frier







Chantelau et al.







Songer et al. (1988)






Vocational Driving Licences

A more stringent approach towards vocational licences, i.e., those for large goods vehicles (LGV) and passenger carrying vehicles (PCV), has been adopted by the European Community, and for several years insulin-treated drivers have been debarred from holding vocational driving licences in most European countries. However, there is a wide international variation in the policies of governments towards vocational licensing for diabetic drivers (DiaMond Project Group on Social Issues, 1993) and even between states in the USA (Gower et al., 1992). The Federal Highways Administration in North America has explored a waiver scheme for insulin-treated diabetic drivers of commercial trucks and those who drive between states, provided they meet strict medical criteria and are free from severe hypoglycaemia, but regulations differ between States.

In Europe, as a consequence of the second EC Directive on driving in 1991, there was a reclassification of vocational licences; people with insulin-treated diabetes are now allowed 'in exceptional circumstances' to drive commercial vehicles, such as vans or lorries, weighing between 3.5 and 7.5 tonnes (3500 to 7500 kg) (with a C1 licence), and mini buses carrying up to 16 passengers (with a D1 licence) for their employment, subject to more stringent annual review of medical fitness to drive. This concession does not include D1 licences in the UK, although an aberration remains in British legislation that allows voluntary drivers with insulin-treated diabetes to drive minibuses, such as for charity work or for voluntary organizations. The main medical concern is the risk of hypoglycaemia affecting drivers of these larger vehicles. The need to safeguard public safety has to be balanced against the rights of the individual with diabetes, but this issue has aroused considerable controversy. Taxi driving is controlled by local authorities and for drivers with diabetes who work for emergency services (such as the police, fire and ambulance services), driving restrictions are determined by the employer, usually with advice from occupational health physicians.

Advice for Diabetic Drivers

Although this chapter is primarily concerned with hypoglycaemia, there are various reasons why an individual driver who is taking insulin may be advised to cease driving, albeit temporarily (Box 14.7). Cox et al. (1994) have claimed that blood glucose awareness training in a small number of people with impaired awareness of hypoglycaemia led to fewer road traffic accidents in subsequent years, suggesting an indirect benefit of this approach to improving the recognition of blood glucose fluctuations (see Chapter 7). Prevention of hypoglycaemia while driving is essential (Box 14.8) and it is important for the driver to plan each journey (no matter how short) in advance. Blood glucose testing is advisable before driving, and at intervals of about two hours during long journeys, and rest periods for snacks and meals should be taken. Unfortunately, this practice is not common. A survey in Edinburgh showed that 50% of 202 insulin-treated diabetic drivers never test blood glucose in relation to driving, and only 14% do this regularly, most of these individuals having impaired awareness of hypoglycaemia (Graveling et al., 2004). Around half of those questioned admitted to a variety of unsafe practices with respect to driving.

Box 14.7 Diabetic drivers - Reasons to cease driving


• People with newly diagnosed type 1 diabetes or any patient commencing treatment with insulin, should cease driving until glycaemic control and vision are stable.

• Recurrent hypoglycaemia (especially if severe).

• Impaired awareness of hypoglycaemia (if disabling).


• Reduced (corrected) visual acuity for distance (worse than 6/12 on Snellen chart) in both eyes. Care required after use of mydriatic for eye examination.

• Sensori-motor peripheral neuropathy with loss of proprioception.

• Severe peripheral vascular disease; lower limb amputation (hand controls and automatic transmission may be feasible).

Box 14.8 Advice for diabetic drivers regarding hypoglycaemia

• If hypoglycaemia occurs while driving, stop the vehicle in a suitable location; leave the driver's seat.

• Always keep an emergency supply of readily accessible fast-acting carbohydrate (e.g. glucose tablets or sweets) in the vehicle.

• Check blood glucose before driving (even on short journeys) and estimate at regular intervals on long journeys.

• Take regular meals and snacks, and rest periods on long journeys; avoid alcohol.

• If hypoglycaemia is experienced, do not drive until 45 minutes after blood glucose is restored to normal (delayed recovery of cognitive function).

• Carry personal identification indicating 'diabetes' in case of injury in a road traffic accident.

A supply of both quick-acting and more substantial carbohydrate should be kept constantly in the vehicle in case of unexpected delays or emergencies (traffic jams, breakdowns) or unpremeditated exercise such as changing a wheel. If hypoglycaemia occurs while driving, the driver should stop the vehicle, switch off the engine and leave the driver's seat, as in British law a charge of driving under the influence of a drug (insulin) can be made even if the car is stationary. It is also important that driving is not recommenced immediately after normoglycaemia is restored. In this situation, blood glucose does not accurately reflect the glucose concentration in the brain, with the rise in intra-cerebral glucose lagging behind that in the peripheral blood. The complete recovery of cognitive function following hypo-glycaemia takes up to 45 minutes after blood glucose has returned to normal (Chapter 2), and so an interval of this duration should be allowed before driving is recommenced.

Medico-legal Aspects

Physicians who specialize in diabetes are often required to provide medical reports in relation to road traffic accidents involving drivers with insulin-treated diabetes, in whom hypogly-caemia has been implicated as a possible cause. A detailed history of the circumstances should be taken from the diabetic driver to identify whether hypoglycaemia was likely at the time of the accident, as contemporaneous blood glucose measurements are seldom available. Occasionally, blood glucose has been measured at the scene of the accident by paramedical ambulance staff or on subsequent admission to hospital. However, any significant delay before the blood glucose is estimated may obscure the glycaemic status at the time of the accident, through the effect of counterregulatory hormones released by the stress of the accident and/or hypoglycaemia per se, or as a result of treatment.

The presentation of a convincing story of hypoglycaemia preceding the accident has to be accompanied by a careful description of the potential effects of hypoglycaemia on cognitive function and behaviour, comprehensible to a lay person. Although this mitigating factor may not allow legal charges to be dismissed, in my experience the penalty may be substantially reduced if hypoglycaemia is accepted to be the principal problem that has affected the individual's driving ability and precipitated the accident. However, this must not be considered to be a foregone conclusion, as the legal view of hypoglycaemia occurring in a person treated with insulin (or an oral hypoglycaemic drug) is that this represents 'careless' or 'reckless' behaviour on their part and is therefore the 'fault' of the individual, even though in clinical practice no specific cause can be determined for many episodes of hypoglycaemia. Although the difficulty of always being able to test blood glucose before driving is recognised in clinical practice, when this has a serious outcome, the judiciary may take a much stricter view. In a case in Edinburgh Sheriff Court in 2000, which involved a fatal car accident caused by a hypoglycaemic diabetic driver, who had not measured his blood glucose before driving, the Sheriff commented: 'There is a risk associated with diabetes and driving, and as a consequence, there is a need to monitor your blood sugar level. There is some culpability on your part'. The driver was found guilty of dangerous driving. By contrast, spontaneous hypoglycaemia is an accepted defence, and one of my patients with insulin-treated diabetes had charges of dangerous driving dismissed when it was shown that at the time of the offence he had developed undiagnosed and untreated Addison's disease -a relatively rare but recognised cause of increased and unpredictable severe hypoglycaemia in type 1 diabetes. Medico-legal aspects of hypoglycaemia and diabetes have been reviewed elsewhere (Frier and Maher, 1988).


Many of the measures recommended for longer car journeys (Box 14.8) are appropriate to long distance travel, irrespective of the mode of transport used. Forward planning is essential to avoid hypoglycaemia, with emphasis on adjustment of insulin dose (or regimen) if necessary, carrying equipment for blood glucose monitoring and ensuring an adequate supply both of quick-acting carbohydrate and of non-perishable emergency rations in case suitable food is not available during travel. Standard airline meals are often low in unrefined carbohydrate and may be unpalatable. Advice for travel and holidays is available from various sources, but with respect to avoiding (and treating) hypoglycaemia, some practical points can be made.

• For long-distance air travel, crossing several time zones, frequent administration of short-acting (soluble or analogue) insulin is much simpler to use than attempting to modify the times of administration and dosage of intermediate-acting insulins. Disposable insulin pens are also very useful for this purpose. Rapid-acting insulin analogues have the advantage that their administration can be delayed until the food on offer is available and its palatability assessed, or can be taken after the meal, providing greater flexibility for treatment.

• Some blood glucose meters are inaccurate in the hypoglycaemic range and many do not give accurate readings at high altitude or at extremes of temperature. Visually-read strips for blood glucose estimation may therefore be necessary in some situations. It is advisable to carry a spare blood glucose monitor in case of equipment failure.

• A supply of quick-acting carbohydrate is essential, but should be stored appropriately. Dextrose tablets may disintegrate or become very hard in hot and humid climates unless wrapped in silver foil or stored in a suitable container, and chocolate will melt if the temperature is high. At very cold temperatures, the wrapper may become welded to the chocolate. Cartons of orange juice cannot be re-used once opened, and so a plastic bottle or container with a screw top is preferable. Sealed packets of powdered glucose may be more suitable to carry in hot humid climates.

• Travelling companions should carry a supply of quick-acting carbohydrate (and glucagon) for emergency use.

The nature of the travel undertaken, how much energy is expended, the quality and nature of food and the risk of intermittent illness (such as travel sickness or gastroenteritis) are all potential factors that can influence blood glucose and potentially induce hypoglycaemia. Although many situations are predictable, the most important measure is frequent monitoring of blood glucose so that sensible adjustments in insulin therapy and ingestion of food can be made.

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