Glucose variability assessed with continuous glucose monitoring: reliability, reference values and correlations with established glycaemic indices - The Maastricht Study.

Glucose variability (GV) measured by continuous glucose monitoring (CGM) has become an accepted marker of glycaemic control. Nevertheless, several methodological aspects of GV assessment require further study. We therefore investigated the minimum number of days needed to reliably measure GV, assessed GV reference values, and studied the correlation of GV with established glycaemic indices (i.e. HbA1c, seven-point OGTT-derived indices).We used cross-sectional data from The Maastricht Study, an observational population-based cohort enriched with type 2 diabetes. Participants with more than 48 hours of CGM (iPro2; Medtronic) were included for analysis (n=851; age: 60±9years; 49% women; 23% type 2 diabetes). We used mean sensor glucose (MSG), standard deviation (SD), and coefficient of variation (CV) as CGM-derived indices (the latter two for GV quantification). We calculated reliability using the Spearman-Brown prophecy formula, established reference values by calculating 2.5th-97.5th percentiles, and studied correlations using Spearman's rho.Sufficient reliability (R>0.80) was achieved with two (MSG and SD), or three monitoring days (CV). The reference ranges, assessed in individuals with normal glucose metabolism (n=470), were 90.5-120.6mg/dL (MSG), 7.9-24.8mg/dL (SD), and 7.74-22.45% (CV). For MSG, the strongest correlation was found with fasting plasma glucose (rho=0.65 [0.61;0.69]); for SD, with the 1-hour OGTT value (rho=0.61 [0.56;0.65]); and for CV, with both the incremental glucose peak (IGP) during the OGTT (rho=0.50 [0.45;0.55]) and the 1-hour OGTT value (rho=0.50 [0.45;0.55]).The reliability findings and reference values are relevant for studies that aim to investigate CGM-measured GV. One-hour OGTT and IGP values can be used as GV indices when CGM is unavailable.