Application of medium-term metrics for assessing glucose homoeostasis: Usefulness, strengths and weaknesses

This review aims to address the issue of whether or not the newer metrics, developed for continuous glucose monitoring [real-time CGM (rtCGM), intermittently scanned CGM (isCGM)], enhance assessment of the "glucose tetrad": Ambient hyperglycaemia, short-term glycaemic variability, postprandial glucose excursions and hypoglycaemia. The ever-increasing number of metrics offered with rtCGM and isCGM includes intermediate-term indicators referred to as "time in range" (TIR), the time spent in the range of 70–180 mg/dL (TIR 70–180); time spent above the range of 180 mg/dL (TAR > 180); and time spent below the range of 70 mg/dL or 54 mg/dL (TBR < 70 or TBR < 54). The former two values are strongly correlated with HbA1c levels and can therefore serve as short- or medium-term markers of ambient hyperglycaemia, depending on whether glucose sensors are worn over periods of several days or weeks, respectively, whereas the latter indices (TBR < 70 or < 54) are more relevant for capturing hypoglycaemic events and quantifying their magnitude and duration, in contrast to random spot testing with self-monitoring of blood glucose. Nevertheless, although analyses of 24 h glucose profiles by CGM provide a highly valuable method for quantifying postprandial glucose excursions and short-term glycaemic variability, neither of these factors can be fully represented by such TIR metrics. Thus, other metrics are clearly needed for more comprehensive assessment of glucose homoeostasis.