To Örebro University

While current systems for continuous glucose monitoring (CGM) are safe and effective, there is a high degree of variability between readings within and across CGM systems. In current CGM performance studies, device readings are compared with glucose concentrations obtained with a comparator ("reference") measurement procedure (usually capillary or venous glucose). However, glucose concentrations from capillary and venous samples can systematically differ, often by as much as 5 to 10%. Different comparator methods have shown biases of up to 8%, and comparator devices of the same brand can systematically differ by more than 5%. To address these issues, the Working Group on CGM of the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC WG-CGM) recommends standardizing study procedures and the comparator measurement process in CGM performance studies. The majority of IFCC WG-CGM members recommend the use of capillary samples as reference, mainly because CGM readings will then be aligned better with results from self-monitoring of blood glucose (SMBG). Even with factory-calibrated CGM systems, manufacturers require CGM users to perform SMBG in some situations, eg, manual calibration, confirmation of extreme readings, discordance between CGM readings and symptoms of hyper- or hypoglycemia, or intermittent signal loss. Comparator devices should meet defined analytical performance specifications for bias and imprecision. Comparator bias can be reduced by retrospective correction of comparator values based on measurements with a method or materials of higher metrological order. Once manufacturers align CGM readings of their systems with comparator results using standardized procedures, variability across CGM systems will be reduced.