Using continuous glucose monitoring to assess contributions of premeal and postmeal glucose levels in diabetic patients treated with metformin alone. 
This study aimed to determine the contributions of basal excess glycaemia (BEG) and prandial excess glycaemia (PEG) to overall excess glycaemia in type 2 diabetes (T2D) patients treated with metformin alone.  Outpatients with T2D treated with metformin alone (n=46) who underwent continuous glucose monitoring (CGM) were divided into tertiles according to glycated haemoglobin (HbA1c) levels.  For each CGM trace, the glucose area under the curve (AUC)>5.5mmol/L was expressed as the AUCoverall, representing overall excess glycaemia.  The sum of glucose AUCs above the premeal glucose level at 4h after breakfast, lunch and dinner was expressed as the AUCpeg, representing PEG.  The contribution of PEG to overall excess glycaemia was calculated as (AUCpeg/AUCoverall)×100%.  The contribution of BEG was calculated as [(AUCoverall-AUCpeg)/AUCoverall]×100%.  Factors related to PEG contribution were also analysed.  BEG constituted more than half the overall excess glycaemia in all HbA1c tertiles.  The contribution of PEG was negatively correlated with HbA1c and mean glucose values before each meal.  Prebreakfast and predinner glucose values were the dominant factors affecting PEG contribution and was independent of HbA1c.  In patients treated with metformin alone, BEG was the major contributor to excess glycaemia at HbA1c levels ≥7.7%, while PEG and BEG contributions were similar and stable below this level.  For HbA1c levels ≥7.7%, add-on therapy to metformin should preferentially target control of BEG, whereas targeting both BEG and PEG could be of equivalent importance with lower HbA1c levels.