Research

Driving and Diabetes

Driving and the EU law
Driving and hypoglycaemia – what are doctors being advised to do?
Test Strips – Department Of Health Warning For Doctors And Pharmacists
Vehicles You Can Drive
Insulin and Driving Taxis
Hypoglycaemia and Driving
Driving and Medicines
Driving and Visual Field Loss

Living with Diabetes

Research

Alcohol, driving and hypoglycaemia
Alcohol can interfere with all aspects of the normal physiological, cognitive and symptomatic responses to hypoglycaemia. In otherwise healthy individuals, the net effect of alcohol on glucose metabolism is neutral, provided that liver glycogen stores are replete. For insulin treated people, the influence of hypoglycaemia is more relevant.

A study conducted in 1990 found that moderate alcohol consumption of 100-120mg/100ml blood,* markedly reduced awareness of hypoglycaemia and slowed down reaction time. The loss of awareness occurred despite the presence of the usual symptoms such as facial flushing, blurred vision, pounding heart and sweating. The patients felt hypo after alcohol when blood alcohol levels were within the normal range but by contrast, the clinical features of low blood glucose can be mistaken for alcohol intoxication.

Even at very low levels of blood alcohol it is possible that there may be a deleterious effect on cognitive performance which may be aggravated if blood glucose levels fall below the threshold which has been shown to impair cognitive performance. It is therefore better not to take any risks with driving and better not to drink at all if driving.

*Current legislation in the UK provides an upper limit of 80mg/100ml blood.

[Kerr et al, Diabetologia 33: 216-21]

The perception of safe driving ability during hypoglycamia in patients with type 1 diabetes
Hypoglycaemia and its subsequent cognitive impairment may place people with diabetes at risk when driving. This study looks at the factors that influence judgements of safe driving ability during hypoglycaemia.

30 men and 30 women who had an average duration of Type 1 diabetes of 9 years and no complications underwent hypoglycaemia with a stepped insulin clamp. Glucose levels were reduced in stages over 190 minutes to 40mg/dL [2.2mmols/l]. At each point the patients completed a symptom questionnaire and a neuropsychological test, estimated their blood glucose level and reported whether they could drive safely. The study was repeated with another 93 patients later in the year and the results were similar.

The proportion of patients judging that they could drive safely decreased as blood glucose levels went down from 70% at 120mg/dL [6.6mmols/l] to 22% at 40mg/dL [2.2mmols/l]. When blood sugars were between 3.3 and 3.9mmols/l the first group said they would drive 60% of the time and the second group 64% of the time. With a blood sugar of less than 2.2 mmols/l the figures were 38% and 47%.

Men and middle-aged patients were more likely to consider it safe to drive during hypoglycaemia than women and those under 25 years. Those who were symptomatic and those who recognised hypoglycaemia were less likely to report ability to drive during hypoglycaemia. Most patients who were cognitively impaired appeared to recognise this and reported that they could not drive safely at blood glucose levels of 40mg/dL [2.2mmols/l]. Glucose levels less than 70mg/dL [3.9mmols/l] should be treated before driving. This information is as important for middle-aged, experienced drivers as it is for younger inexperienced drivers.

The author is quoted in the Pharmaceutical Journal 28.8.99 "Given the relatively low level of low blood glucose detection, the suggestion that individuals measure their blood glucose levels and raise potentially low blood glucose levels before driving does not seem unreasonable."

Am J Med 1999 Sep; 107(3):246-53