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

Chronic exposure to elevated glucose is a central feature of dysglycemia across the spectrum from prediabetes to diabetes. Continuous glucose monitoring (CGM) provides rich temporal glucose data, but effective summarization that integrates the magnitude and duration of sustained hyperglycemia into a single and parameter-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. 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. Analysis of a public CGM dataset showed strong correlations between GPI and daily mean glucose and glucose variance, while substantial heterogeneity at fixed GPI values indicated that GPI captures complementary information beyond average exposure or overall variability. 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.