Discrepancies between current displayed and auto-logged glucose values in FreeStyle Libre 3: Implications for clinical interpretation.

Abstract

Aims: The FreeStyle Libre 3 (FSL3) continuous glucose monitoring (CGM) system provides both auto-logged glucose values (AL) and current displayed glucose values (CUR). These values are often assumed to be interchangeable; however, discrepancies and their clinical relevance remain underexplored.

Materials and methods: Data from a 15-day study in 24 study participants wearing FSL3 were analysed, including three in-clinic sessions with glycaemic excursions during which CUR values were retrieved every 15 min by study personnel. Paired AL and CUR readings were compared using descriptive statistics, Wilcoxon signed-rank tests, and mean absolute relative difference (MARD) calculations. Display errors defined as instances where the app showed an error message instead of a CUR value were analysed using linear mixed-effects models to assess associations with glucose level and rate of change (RoC).

Results: CUR values were comparable to AL in general (mean difference: -1.2 ± 6.4 mg/dL), but slightly lower in the hypoglycaemic range. Discrepancies exceeding ±10 mg/dL occurred in about 10% of cases. MARD was comparable between AL (9.7%) and CUR (10.1%), with greater deviation in hypoglycaemia. Display errors (3.9%) occurred more often at higher glucose levels (mean AL difference: +91.9 mg/dL) and during rapid fluctuations (mean absolute RoC difference: +1.52 mg/dL/min; both p < 0.001).

Conclusions: Although differences between AL and CUR were generally small, they were systematic and more pronounced in critical contexts like hypoglycaemia and rapid glucose change. Recognising these patterns may improve CGM data interpretation and alignment between user actions, provider decisions, and automated systems. These differences can reclassify readings across clinical thresholds, affecting patient-clinician alignment despite small average biases.