Hypoglycemia significantly impairs driving performance (1, 2), and driving collisions involving diabetic individuals are frequently attributed to hypoglycemia (3). Further, driving mishaps are often preceded by frequent mild symptomatic hypoglycemia while driving (4). It is reasonable to expect that before a hypoglycemia-related driving mishap, drivers with type 1 diabetes may experience frequent episodes of hypoglycemia.

We recently conducted a study in which 100 adults and 100 children with type 1 diabetes were given memory meters and strips (OneTouch Ultra; LifeScan, Milpitas, CA) and asked to record all blood glucose readings for 6 consecutive months. Tragically, during this study, two subjects died in vehicular collisions. Subject A was a 47-year-old male with a 30-year history of type 1 diabetes and an HbA1c (A1C) of 7.6%. Witnesses reported that the subject had been swerving out of his lane, with erratic speed, and was unresponsive to the honks of other drivers before crashing into a tree. Subject B was a 15-year-old male with a 7-year history of type 1 diabetes and an A1C of 7.0%. The accident occurred when his ATV flipped while driving through the woods.

The low blood glucose index (LBGI) is a composite score reflecting the frequency and extent of low blood glucose over a month of routine self-monitoring of blood glucose (57). The LBGI accounts for 40–60% of the variance of future severe hypoglycemic episodes within the following 3–6 months (57), whereas A1C accounts for only 6% of the variance (8). An LBGI of >5 places an individual at significantly elevated risk of future severe hypoglycemic episodes; this represents a 10-fold increase in the occurrence of future severe hypoglycemic episodes compared with an LBGI of <2.5 (57). The LBGI can significantly change within 2–4 weeks with changes in diabetes regimen, while A1C is a more stable measure, taking 2–3 months to incur a significant change.

After the second death, we analyzed memory meter data for subjects’ LBGI. For the 3 months before these fatalities, monthly LBGI steadily rose for subject A from 6.2, to 7.0, to 7.5 and for subject B from 3.3, to 5.0, to 6.6. During this period, subject A reported four episodes of severe hypoglycemia, while subject B experienced one episode of severe hypoglycemia the week before the collision.

If these individuals had been informed about their elevating risk of future severe hypoglycemia and given the opportunity to reduce this risk, these deaths may have been avoided. It must be pointed out that the LBGI is certainly not specific to driving collisions. Currently, the LBGI is not available to patients on any memory meter display program, but its computation is straightforward and can be computed on any data spreadsheet. A less sophisticated and less sensitive alternative is to have patients compute the percent of blood glucose readings <3.9 mmol/l. An LBGI ≥5 is equal to roughly >15% of an individual’s self-monitoring of blood glucose readings being <3.9 mmol/l. If patients recognize when they are having frequent low blood glucose values and take steps to reverse this, it is possible that some of these tragic events could be avoided. It is exposure to frequent hypoglycemia, not low A1C, that increases the risk of severe hypoglycemic episodes (57).

This research was supported by National Institutes of Health Grants R01 DK28288 and R01 DK 51562 and a grant from LifeScan.

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