A Driving Risk with Too Tight Diabetes Control?

Toronto, Canada, researchers investigated the circumstances surrounding motor vehicle crashes by diabetics.  Their findings are posted in the online journal Public Library of Science (PLoS): Medicine.

The study subjects were 795 consecutive drivers reported to the vehicle licensing authorities over a 2-year period who had a diagnosis of diabetes and a documented HbA1c level.  There were 57 patients involved in a crash and 738 who were not.  The average HbA1c level was lower for those in a crash than in the others – 7.4% vs. 7.9%.  This equated to a 26% increased risk of having a crash for every 1% reduction in HbA1c.  The risk increased 4-fold if the person had a history of severe hypoglycemia requiring outside assistance.  It was also increased if diagnosis of diabetes was made at a later age.

Roughly 8% of the US population has diabetes, of whom about 90% have type 2 diabetes.  Advanced disease can be associated with complications that would obviously impair driving skills; in particular eyesight (diabetic retinopathy) and nerve function (diabetic neuropathy).  In this group of patients, a lower HbA1c represented ‘tighter control’.  But hypoglycemia is a risk of tight control, and awareness of the early signs of a hypo episode is not always adequate, especially in the elderly.  Indeed, over time some diabetics can become less aware of the early symptoms of hypoglycemia. 

In some countries driver licensing authorities require evidence that a diabetic’s condition is ‘well-controlled’ before they’ll issue a license.  And the HbA1c is one measure of this.  Obviously, this study shows that the HbA1c is a poor measure to use to avoid having drivers at risk.  The answer to this dilemma is to make sure that diabetics are clearly aware of the early symptoms of hypoglycemia, and know when they should act on this.