The perception of safe driving ability during hypoglycemia in patients with type 1 diabetes mellitus

PURPOSE: Insulin-induced hypoglycemia and its sequelae of cognitive impairm ent may place patients with type 1 diabetes at risk when driving and when m aking decisions about driving. Little is known about the factors that influ ence judgments of safe driving ability during hypoglycemia in these patient s. PATIENTS AND METHODS: Thirty men and 30 women with uncomplicated type I dia betes (age [mean +/- SD] 33 +/- 9 years, duration 9 +/- 3 years, hemoglobin A(1c) level 8.7% +/- 1.0%) un derwent a stepped hypoglycemic insulin damp. Serum glucose levels were reduced from 120 mg/dL to 80, 70, 60, 50, and th en 40 mg/dL during 190 minutes. At ach glucose plateau, patients completed a symptom questionnaire and neuropsychological test, estimated their glucos e level, and reported whether they could drive safely. RESULTS: The proportion of patients judging that they could drive safely de creased as serum glucose levels decreased from 70% at 120 mg/dL to 22% at 4 0 mg/dL. Men and middle-aged patients were more likely to consider it safe to drive during hypoglycemia than women and chose under 25 years of age. Th ose who were symptomatic and those who recognized hypoglycemia were less li kely to report safe driving ability during hypoglycemia. Most patients who were cognitively impaired appeared to recognize this and reported that they could not drive safely at a serum glucose level of 40 mg/dL. CONCLUSIONS: Adults with type 1 diabetes need educational reinforcement of safe driving habits, particularly to check glucose levels before driving. G lucose levels less than 70 mg/dL should be treated before driving. This inf ormation is as important for middle-aged, experienced drivers as it is for younger, inexperienced drivers. (C) 1999 by Excerpta Medica, Inc.