The significance of coefficient of variation as a measure of hypoglycaemia risk and glycaemic control in real world users of the automated insulin delivery MiniMed 780G system

Aim: Use of the MiniMed 780G system (MM780G) can result in a reduction in mean and standard deviation (SD) of sensor glucose (SG) values. We assessed the significance of the coefficient of variation (CV) as a measure of hypoglycaemia risk and glycaemic control. Materials and Methods: Data from 10 404 MM780G users were analysed using multivariable logistic regression to assess the contribution of CV to (a) hypoglycaemia risk, measured as not reaching target <1% for time below range (TBR), and (b) achieving targets of time-in-range (TIR) >70% and glucose management indicator <7%. CV was compared with SD and low blood glucose index. To assess the relevance of CV <36% as a therapeutic threshold, we identified the CV cut-off point that optimally discriminated users at risk of hypoglycaemia. Results: The contribution of CV was the smallest in terms of risk of hypoglycaemia (vs. low blood glucose index and SD) and TIR and glucose management indicator targets (vs. SD). In all cases the models with SD showed the best fit. A CV <43.4% (95% CI: 42.9–43.9) was the optimal cut-off point with a correct classification rate of 87.2% (vs. 72.9% for CV <36%). Conclusion: For MM780G users, CV is a poor marker for hypoglycaemia risk and glycaemic control. We recommend using, for the former, TBR and whether the TBR target is met (and not using CV <36% as a therapeutic threshold for hypoglycaemia); for the latter, TIR, time above range, whether targets are met and a discrete description of mean SG and SD of SG values.