Two articles from reputable Diabetes Medical Journals in 2000 and in 1998, suggest that  diabetics should not drive if their blood glucose is below 100mg/dl (6.7mmol/L)

Diabetes, hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) and driving capacity

Original article:
Progressive hypoglycemia’s impact on driving simulation performance. Occurrence, awareness, and correction. Cox DJ, Gonder-Frederick LA, Kovatchev BP et al. Diabetes Care 2000; 23(2): 163–70.

Summary
Progressive hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) leads to cognitive-motor and driving impairments. This study evaluated the blood glucose levels at which driving was impaired, impairment was detected, and corrective action was taken by subjects, together with the mechanisms underlying these three issues.

Thirty-seven adults with Type 1 diabetes drove a simulator during continuous euglycaemia and progressive hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ). During testing, driving performance, EEG and corrective behaviours (drinking a soda or discontinuing driving) were continually monitored, and blood glucose, symptom perception and judgement concerning impairment were assessed every 5 min. Mean ± SD euglycaemia performance was used to quantify z-scores for performance in three hypoglycaemic ranges: 4.0–3.4, 3.3–2.8 and <2.8 mmol/l.

During all three hypoglycaemic blood glucose ranges, driving was significantly impaired and subjects were aware of their impaired driving. However, corrective actions did not occur until blood glucose was <2.8 mmol/l. Driving impairment was related to increased neurogenic symptoms and increased theta-wave activity. Awareness of impaired driving was associated with neuroglycopenic symptoms, increased beta-wave activity, and awareness of hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ). High beta- and low theta-wave activity and awareness of both hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) and the need to treat low blood glucose influenced corrective behaviour.

The authors conclude that driving performance is significantly disrupted at relatively mild hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ), yet subjects hesitated to take corrective action. The longer treatment is delayed, the greater the neuroglycopenia (increased theta-wave activity), which precludes corrective behaviours. Patients should self-treat while driving as soon as low blood glucose and/or impaired driving is suspected and should not begin driving when their blood glucose is in the 5.0–4.0 mmol/l range without prophylactic treatment.

Comment

It is now well established that people with diabetes as a group do not have higher accident rates than their non-diabetic counterparts [1–6]; two studies even suggest a decreased risk among people with diabetes [7, 8]. This might be explained by the fact that people with diabetes as a group drive more carefully (e.g. lower alcohol consumption, more frequent stops during long distance drives, better respect for general driving regulations). Moreover, whereas alcohol is the most important human factor in road traffic accidents, hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) is very rarely implicated [9]. These favourable observations mean that insulin-treated people in most countries of the world face no additional restrictions to their ability to hold a driving licence.

However amongst those with insulin-treated diabetes, some may indeed be at high risk of road traffic accidents, i.e. those with impaired hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) awareness, a phenomenon that may be present in up to 25% of Type 1 diabetics [10, 11]. Clearly, access to a driving licence (for both professional and private purposes) should be strictly regulated in those with hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) unawareness, and the technique for restoring hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) awareness by avoiding hypoglycaemic episodes for several weeks should be widely used [12, 13].

This study by Cox et al. once more underlines the importance of the problem of reduced hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) awareness: 15% of the 37 subjects tested detected hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) when their blood glucose value was between 4.0 and 3.4 mmol/l; 33% when their blood glucose value was between 3.3 and 2.8 mmol/l; and 79% when their blood glucose fell below 2.8 mmol/l (Table I). 

Table I: Driving performance at three levels of hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ).

Above all, it specifically emphasizes the fact that even when subjects recognized their hypoglycaemic state, only 5% took corrective action at blood glucose 4.0–3.4 mmol/l, 3% at blood glucose 3.3–2.8%, and 22% at blood glucose <2.8 mmol/l (Table I), indicating that more than 70% of the tested subjects, under experimental driving conditions, did not take corrective action for their hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) even at a blood glucose level below 2.8 mmol/l. Moreover their driving performance score was significantly reduced during hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) (p < 0.01 for blood glucose 4.0–3.4 mmol/l and p < 0.005 for blood glucose 3.3–2.8 and <2.8 mmol/l) (Table I).

This study demonstrates that hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) is a significant factor in impaired driving and that patients are generally aware of when their 

driving performance is deteriorating. However, the data also indicate that patients are unlikely to treat their low blood glucose while driving. In large part, this appears to be due to waiting too long before taking corrective action. The results therefore suggest that patients should be encouraged to treat themselves immediately, whenever they think their blood glucose is low or their driving ability is impaired, and not wait until they become too neuroglycopenic or their driving ability too impaired.

As stated by Marrero and Edelman in their editorial [14]: ‘It is obviously important that we teach strategies for avoiding hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) that are specific to driving. Blood glucose testing before driving needs to be stressed and minimum glucose values for safely operating a motor vehicle need to be established.’

Diabetes educators should impress on their patients the importance of:

– measuring blood glucose before beginning to drive,
– eating a sugar-containing snack if blood glucose is below 100 mg/dl,
– regularly stopping and checking their blood glucose on long distance drives,
– not drinking alcohol while driving,
– having a sugar-containing snack within easy reach,
– if they have any strange feelings while driving, to pull over immediately and park the car, measure blood glucose and if it is low, take corrective measures and wait 45 min before driving on.
Efforts to make these suggestions may impede the need for a more thoughtful educational response to minimizing possible accidents that may be caused by hypoglycaemic episodes.

References

 1. Distiller LA, Kramer BD. Driving and diabetics on insulin therapy. S Afr Med J 1996; 86: 1018–20.
 2. Veneman TF. Diabetes mellitus and traffic incidents. Neth J Med 1996; 48: 24–8.
 3. Koepsell TD, Wolf ME, McCloskey LM et al. Medical conditions and motor vehicle collision injuries in older adults. J Am Geriatr Soc 1994; 42: 695–700.
 4. Gonder-Frederick LA, Cox DJ, Driesen NR et al. Individual differences in the neurobehavioral disruption during mild and moderate hypoglycemia in adults with IDDM. Diabetes 1994; 43: 1407–12.
 5. Driesen NR, Cox DJ, Gonder-Frederick LA, Clarke WL. Reaction time impairment in insulin-dependent diabetes: task complexity, blood glucose levels, and individual differences. Neuropsychology 1995; 9: 246–54.
 6. Cox DJ, Gonder-Frederick LA, Julian DM, Clarke WL. Long-term follow-up evaluation of blood glucose awareness training. Diabetes Care 1994; 17: 1–5. 
 7. Cox DJ, Gonder-Frederick LA, Kovatchev B et al Reduction of severe hypoglycemia (SH) with blood glucose awareness training (BGAT-2) [abstract]. Diabetes 1995; (suppl 1): 27A.
 8. Cox DJ, Gonder-Frederick LA, Clarke WL. Driving decrements in type 1 diabetes during moderate hypoglycemia. Diabetes 1993; 42: 239–43.
 9. MacLeod KM. Diabetes and driving: towards equitable, evidence-based decision-making. Diabetic Med 1999; 16: 282–90.
10. Gerich JE, Mokan M, Veneman T et al. Hypoglycemia unawareness. Endocr Rev 1991; 12: 356–71.
11. Frier BM. Hypoglycemia unawareness. In: Frier BM, Fischer BM, eds. Hypoglycemia and diabetes: clinical and physiological aspects. London: Edward Arnold, 1993; 284–301.
12. Cranston I, Lomas J, Maran A et al. Restoration of hypoglycaemia ( hypoglycemia , insulin shock, insulin reaction ) awareness in patients with long duration insulin-dependent diabetes. Lancet 1994; 344: 283–7.
13. Lingenfelser T, Buettner U, Martin J et al. Improvement of impaired counterregulatory hormone response and symptom perception by short-term avoidance of hypoglycemia in IDDM. Diabetes Care 1995; 18: 321–5.
14. Marrero D, Edelman S. Hypoglycemia and driving performance. A flashing yellow light? [editorial]. Diabetes Care 2000; 23: 146–7.

Summary and Comment:
Georges Krzentowski, Jumet, Belgium

ADA CONFERENCE: Mild Hypoglycemia Impairs Driving In Type I Diabetics

CHICAGO, IL -- June 16, 1998 -- For people with Type I diabetes, episodes of even mild hypoglycemia can make driving dangerous, according to researchers at the University of Virginia Health Sciences Center.

The finding was reported today at the annual meeting of the American Diabetes Association in Chicago.

"Based on the results of this study, we are recommending that people with diabetes should never get behind the wheel of a car if their blood glucose level is 80 mg/dl or less," said Daniel Cox, professor of psychiatric medicine at U.Va. and the study's lead investigator. "If they are driving and suspect that their blood glucose is getting low, they should pull over and treat it immediately."

Prior to the U.Va. study, doctors thought that a blood glucose level of less than 60mg/dl could result in impaired driving capability. Hypoglycemia starves the brain of glucose energy, which is essential for proper brain function. Lack of glucose energy to the brain can cause symptoms ranging from headache, mild confusion and abnormal behaviour to loss of consciousness, seizure and coma.

In the U.Va. study, 37 adults with Type I diabetes and a history of severe hypoglycemia were tested using a sophisticated driving simulator and a gradual induction of hypoglycemia. During the two, 30-minute testing sessions, the subjects' driving performance, electroencephalogram (EEG) and self-treatment of low blood glucose (BG) were continually monitored. At the same time, BG level, symptom perception and judgement concerning driving impairment and the need to self treat were assessed every five minutes.

To objectively assess driving in a controlled environment, the Atari Research Driving Simulator was utilised. The simulator has three, 25-inch computer screens that wrap around the driver, providing a 160- degree visual field, along with a programmed rear view mirror depicting rear traffic. The driving environment was realistic, incorporating a typical-sized steering wheel, gas and brake pedals, seat and seat belt, Cox said.

Driving performance feedback was provided to the subject visually through the three screens that updated at a rate of 60 times per second; aurally through quadraphonic speakers delivering engine, tire and road noises; and kinesthetically through the steering wheel and pedal pressure. Patients were kept blind to the BG manipulations and actual BG levels.

Results of the study show that driving was significantly impaired during all three hypoglycemic BG ranges tested -- 72 to 61, 60 to 50 and less than 50 mg/dl. In addition, subjects were aware of both the need to treat their low BG and their impaired driving. However, actual treatment of low BG did not occur until BG was less than 50 mg/dl.

"Although other studies show that individuals with diabetes have no more driving accidents than the general population, when they do, it is often due to hypoglycemia," Cox said. "Prevention of hypoglycemia-related accidents relies on both a driver's ability to recognise that BG is low and then to take corrective actions of consuming carbohydrates and/or pulling off the road.

“Our study showed that even when the subjects suspected that their blood glucose was low, they waited too long to treat it, with potentially dangerous consequences."

Editorial notes:

Much of what is being said here is simply not true. The Frequency and Incidence of Diabetic Automobile accidents has been rising dramatically since 1983. The Facts reveal that 60-70% or more of diabetics suffer unnoticed hypoglycemia well below 60 mg/dl (4.0 mmol/L) on the "new" synthetic insulins when they use the MiniMed CGM (Continuous Glucose Monitor).

This shows the propagandistic lies of blaming the patient for waiting too long. If you do not have hypoglycemia symptoms, you can't be waiting, you are too busy dying, maiming yourself or doing one or the other to innocent bystanders!

We have been trying to warn the diabetes community of this problem since February of 1989. Don't even turn you car on if your BG is below 100 mg/dl or 5.5 mmol/L!! That is the experts, NOT me saying this.

PLEASE DON'T DRIVE WITH A BG UNDER 100 mg/dl (6.7 mmol/L).