Percent Time Below Range Is Strongly Associated with Clinically Important Level 2 Hypoglycemia Events in Individuals with Type 1 Diabetes

Objective: To evaluate the relationship between continuous glucose monitoring (CGM)-measured % time <54 mg/dL (% T < 54) and level 2 hypoglycemic events (L2 events; ≥15 min <54 mg/dL) in individuals with type 1 diabetes (T1D). Methods: These analyses examined the associations between CGM-measured % T < 54 and L2 events from eight clinical trials over 3–6 months in participants with T1D. Results: Data from 1532 participants with T1D were analyzed (mean age 37 ± 21 years; 72% adults): 43% using automated insulin delivery (AID), 43% CGM users not using AID (34% multiple daily injections [MDI]; 66% standard pump), and 14% self-monitoring blood glucose (SMBG) users not using CGM (58% MDI; 42% standard pump). There was a strong correlation between % T < 54 and L2 event rate ( r = 0.97), but the relationship differed by the average duration of L2 events. For those with 1% T < 54, the predicted L2 event rate per week was 2.4 events for those with short L2 events (average <30 min), 1.9 events for those with medium duration of L2 events (average 30–60 min), and 1.2 events for those with long L2 events (average >60 min). Those meeting hypoglycemic targets (<1% T < 54) had on average 0.6 L2 events per week, irrespective of technology use. Those not meeting targets (≥1% T < 54) had on average 2.9 L2 events per week, but this differed based on technology use and observed % T < 54. Conclusions: L2 event frequency and % T < 54 are strongly correlated, but the relationship differs by L2 event duration. Therefore, both frequency and duration of L2 events should be reported together. Time-below-range metrics incorporate both aspects and are core CGM endpoints that summarize overall amount of hypoglycemia exposure.