TORONTO - Doctors' warnings to patients that they are potentially medically unfit to drive a motor vehicle can significantly reduce the incidence of serious road crashes, a study suggests.
"We found that each warning led to about a 40 to 50 per cent decrease in the risk of a serious road crash for the patient," said principal researcher Dr. Donald Redelmeier, a senior scientist at the Institute for Clinical Evaluative Sciences.
"This decrease was immediate in onset, profound in magnitude and sustained in duration," said Redelmeier. "An effect of this magnitude is about two times larger than the combined effects of modern trauma hospitals on saving people's lives."
Chronic medical conditions — among them, dementia, strokes, alcoholism, epilepsy and diabetes — can make it risky for patients to get behind the wheel; these conditions contribute to about one-third of all traffic crashes.
Since 1968, Ontario doctors have been required by law to report unfit drivers, but studies have shown that actual reporting of affected patients falls far below the prevalence of chronic diseases like dementia, alcoholism and diabetes in the population, Redelmeier said.
In 2006, physicians in the province began receiving a small fee — $36.25 — for counselling a patient that he or she should not be driving, and reporting them to the Ministry of Transportation.
Redelmeier and his team set out to see what effect a warning might have on the risk of having a serious road crash.
Their paper, published Wednesday in the New England Journal of Medicine, used provincial health records to identify more than 100,000 patients who had received medical warnings from their doctors between April 2006 and March 2010.
The researchers then evaluated each driver's need for emergency care to treat serious injury from a road crash in the four years prior to their warning and the year after. In all, these drivers were involved in about 1,700 severe traffic accidents.
They found there was a 45 per cent drop in serious trauma from motor vehicle crashes in the 12 months after patients were warned they could be courting disaster by getting behind the wheel.
Redelmeier said only 10 to 30 per cent of patients deemed unfit to drive by their doctors end up having their licences suspended; most get "a rather stiff warning letter" from the Ministry of Transport instead, he said.
"So although the majority retain their licence, they lose their peace of mind. So on account of that, some of them probably stop driving, whereas others just stop driving as recklessly. They actually stop at stop signs and they yield the right of way ... and they don't speed."
While doctors' warnings appear to have a benefit in reducing traffic injuries, they also have downsides, he conceded.
The study found that the rate of depression was 25 per cent higher in the year after patients were told they were medically unfit to drive, a depression severe enough to send them to a hospital emergency department.
Researchers also found that an unfit-driver warning could erode the doctor-patient relationship.
"About one out of every five patients never makes a return visit to the physician responsible for giving the warning," said Redelmeier. "So they don't leave the system, but they do take their business elsewhere."
But he said that's no reason for doctors to avoid telling patients they could be putting themselves, their passengers, other drivers and pedestrians in danger.
"It's not a reason to withhold the warning, instead it's a reason for trying to provide the warning in a thoughtful and compassionate manner."