Defining a glycemic persistence index (GPI) for continuous glucose monitoring

Sustained hyperglycemia is the core driver of diabetes complications. Continuous glucose monitoring (CGM) provides rich temporal glucose data, but effective summarization that integrates both magnitude and duration of sustained hyperglycemia into a single and paramter-free scalar remains challenging. We introduce the glycemic persistence index (GPI), a simple, threshold-free CGM-derived metric defined as the largest integer k such that at least k minutes are spent at glucose levels ≥ k mg/dL within a day. For example, a GPI of 125 means that glucose levels were ≥ 125 mg/dL for at least 125 minutes during that day. Geometrically, after ranking glucose values in decreasing order, GPI is given by the intersection at which glucose level and cumulative duration take the same value. Using CGM data from the International Diabetes Closed Loop randomized trial (168 adults with type 1 diabetes), GPI sensitively captured closed-loop treatment benefit with significantly lower values in the closed-loop group compared with sensor-augmented pump therapy (P = 0.0001). GPI correlated with HbA1c and daily mean glucose, while distinguishing patterns of sustained hyperglycemia among individuals with similar conventional metrics. As a simple, device-independent, and threshold-free scalar, GPI quantifies hyperglycemia by jointly capturing its magnitude and duration, enabling consistent and intuitive glycemic profiling accessible to both specialists and non-specialists.