Estimating plasma glucose with the FreeStyle Libre Pro continuous glucose monitor during oral glucose tolerance tests in youth without diabetes

Few studies have assessed the accuracy of the FreeStyle Libre Pro (FLP) continuous glucose monitor for estimating plasma glucose (PG) in non-diabetic children. Objective Determine the accuracy of FLP compared to PG during OGTT in healthy children. Subjects Children (7-11.99 years) with healthy weight and overweight/obesity (n = 33; 52% male). Methods Participants wore the FLP before and during a 2-hour OGTT; PG was measured at 30 minutes intervals. Potential systematic- and magnitude-related biases for FLP vs PG were examined. Results FLP 15-minute averages and PG were correlated at most timepoints during OGTT (r2 = 0.35-0.69, P's < .001 for time point 30-120 minutes) and for PG area under the curve (AUC) (r2 = 0.65, P < .0001). There were no systematic biases as assessed by Bland-Altman analyses for FLP AUC or for FLP at each OGTT timepoint. However, for fasting glucose, a significant magnitude bias was noted (r2 = 0.38, P < .001), such that lower PG was underestimated, and higher PG was overestimated by FLP readings; further, there was poor correlation between fasting PG and FLP (r2 = 0.06, P = .22). BMIz was also associated with FLP accuracy: FLP overestimated PG in children with low BMIz and underestimated PG in those with overweight/obesity for OGTT AUC and OGTT PG at baseline, 60, and 120 minutes (all P's ≤ .015). No adverse events occurred with FLP. Conclusions Among children without diabetes, the FLP was well tolerated and correlated with post-OGTT glucose, but had magnitude bias affecting fasting glucose and appeared to underestimate plasma glucose in those with overweight/obesity. These results suggest potential limitations for the utility of the FLP for research.