Hypoglycemia and the decision to drive a motor vehicle by persons with diabetes

Context Laboratory studies have shown impairments in driving performance am ong subjects with type 1 diabetes mellitus when their blood glucose (BG) le vel is between 2.6 and 3.6 mmol/L (47-65 mg/dL), However, to our knowledge, no data exist examining subjects' decisions to drive at various BC levels during their daily routine, Objective To examine type 1 diabetic subjects' decisions to drive during th eir daily routine based on perception of BG levels compared with actual mea sured BC; levels. Design and Setting Two separate groups of patients were recruited 2 years a part from 4 academic medical centers. Participants All subjects were adults with type 1 diabetes who were drivers and who performed at least 2 BC tests per day. Group 1 (initial) subjects (n = 65) had a mean (SD) age of 38.6 (8.9) years with a mean (SD) diabetes duration of 20.5 (10.6) years, were taking 38.8 (16.8) U/d of insulin, and had a mean (SD) glycosylated hemoglobin (HbA(1)) level of 10.0% (1.9%), Gro up 2 (replication) subjects (n = 93) were 35.8 (8.0) years old with a mean diabetes duration of 17.0 (10.6) years, were taking 40.0 (15.5) U/d of insu lin, and had a mean (SD) HbA(1) level of 8.5% (1.6%). Each subject used a h andheld computer to record data on symptoms, cognitive function, insulin do sage, food, activity, estimated and actual BC levels, and whether he/she wo uld drive. Data were entered 3 to 6 times per day for a total of 50 to 70 c ollections per subject during a 3- to 4-week period. Main outcome Measures Decisions to drive when subjects estimated their BC l evel to be less than 2.2 mmol/L (40 mg/dL), 2.2 to 2.8 mmol/L (40-50 mg/dL) , 2.8 to 3.3 mmol/L (50-60 mg/dL), 3.3 to 3.9 mmol/L (60-70 mg/dL), 3.9 to 10 mmol/L (70-180 mg/dL), and more than 10 mmol/L (>180 mg/dL), and driving decisions when actual BG levels were in these ranges. Results Subjects stated they would drive 43% to 44% of the time when they e stimated their BG level to be 3.3 to 3.9 mmol/L (60-70 mg/dL), and 38% to 4 7% of the time when their actual BC level was less than 2.2 mmol/L (40 mg/d L), Logistic regression analysis demonstrated that number of autonomic symp toms, degree of impairment on cognitive function tests, and BC level estima te predicted 76% to 80% of decisions to drive (P < .01 for all). Approximat ely 50% of subjects in each group decided to drive at least 50% of the time when their BG level was less than 3.9 mmol/L (70 mg/dL), Conclusions Our data suggest that persons with type 1 diabetes may not judg e correctly when their BC level is too low to permit safe driving and may c onsider driving with a low BC level even when they are aware of the low lev el. Health care professionals should counsel their patients about the risk of driving with hypoglycemia and the importance of measuring BG level befor e driving.