ESPE Yearbook of Paediatric Endocrinology

In Brief: The authors investigated intraperson variability in fasting glucose (FG) levels using continuous glucose monitoring (CGM) devices in 8315 nondiabetic adults aged 40–70 years. Day-to-day intraperson standard deviation of FG was 7.52 mg/dl (0.42 mol/l). This high variability has a large estimated impact on the classification of glycemic status (normal FG, prediabetes or diabetes). Of 5328 adults classified as having normal FG based on their Day 1 measurement, 40% and 3% would be reclassified to prediabetes and diabetes, respectively, based on subsequent measurements.

It is likely that many of the diagnostic tests used in endocrinology and diabetes have poor reproducibility. This is likely due to physiological variation, as well as changes in preceding diets and behaviours. The use of repeated testing is limited by resources and participant burden. CGM provides access to several orders of magnitude more data than our traditional single clinic measurement for FG. FG was appropriately defined as measurements during the morning (between 0600 h and 0900 h) after a minimum 8 h fasting. Notably, while duration of fasting varied from 8 to 12 h, this was not correlated with FG values (Pearson, r =0.02).

Of the 5328 adults classified as having normal FG by their Day 1 measurement, only 3030 (57%) also had all other FG measurements in the normal range. Individuals with higher FG variability (FG variance) reported diets with higher % carbohydrates, but had no differences in BMI, waist circumference, body fat or other cardiometabolic parameters.

The authors caution against basing diagnoses on only 1 or 2 FG values, and suggest use of CGM data to provide more reliable glycemic status assessment. As increasing diagnoses of diabetes and prediabetes are made based on HbA1c values, similar assessment of its reproducibility are needed.