The Relationship Between Percent Time <70 mg/dL and Percent Time <54 mg/dL Measured by Continuous Glucose Monitoring

Objective: While it is recognized that there is a strong relationship between the amount of time glucose levels are <70 mg/dL (T-<70) and the amount of time <54 mg/dL (T-<54), the association has not been well quantified.Methods: Datasets with Dexcom continuous glucose monitoring (CGM) data from nine type 1 diabetes randomized trials were pooled to evaluate the relationship between CGM-measured T-<70 and T-<54. Penalized B-spline regression lines were fitted to assess the relationship between T-<70 and T-<54 for blinded CGM use, unblinded CGM use without an automated insulin delivery (AID) system, and unblinded CGM use with an AID system. Results: For blinded data, the T-<54 : T-<70 ratio varied from 19% when the amount of T-<70 was <1% to 44% when the amount of T-<70 was >= 7% whereas for unblinded data the ratio varied from 15% to 42%, respectively. When T-<70 was 4%, the predicted T-<54 was 1.18%, 0.94%, and 0.91% for the blinded, unblinded, and AID data, respectively (P<0.001 comparing blinded versus unblinded and AID).Conclusions: The T-<54 : T-<70 ratio increases with greater T-<70, and the ratio generally is higher with blinded than unblinded CGM data, with the latter appearing to be similar to AID system data. The finding of greater T-<54 for a given T-<70 with blinded CGM data is presumed to be due to an action being taken by the unblinded CGM user and/or by the AID system to minimize hypoglycemia which will have the effect of reducing the amount of T-<54.