Episodes of severe hypoglycemia in type 1 diabetes are preceded and followed within 48 hours by measurable disturbances in blood glucose

This study quantifies blood glucose (BG) disturbances occurring before and after episodes of severe hypoglycemia (SH). For 6-8 months, 85 individuals with type 1 diabetes and a history of SH (age, 44 +/- 10 yr; 41 women and 4 4 men; duration of diabetes, 26 +/- 11 yr; hemoglobin A(1c), 7.7 +/- 1.1%) used Lifescan. One Touch BG meters for self-monitoring three to five times daily and recorded the date and time of SH episodes in diaries. For each su bject, the timing of SH episodes was located in the temporal stream of SMBG readings recorded by the meter, and characteristics, including the Low BG index (LBGI), were computed in 24-h increments. In the 24-h period before t he SH episode LBGI rose (P < 0.001), average BG was lower (P = 0.001), and BG Variance increased (P = 0.001). In the 24 h after SH, LBGI and BG varian ce remained elevated (P < 0.001), but average BG returned to baseline. Thes e disturbances disappeared in 48 h. On the basis of LBGI we identified subj ects at low, moderate, and high risk of SH, who reported, on the average, 1 .7, 3.4, and 7.4 SH episodes (P < 0.005) during the study. In addition, we designed an algorithm that predicted 50% of all SH episodes that occurred i n this subject group. We conclude that episodes of SH are preceded and foll owed by quantifiable BG disturbances, which could be used to devise warning s of imminent SH.