Asymptomatic glycemic instability: how to measure it and which clinical applications?

The glycemic variations observed in nondiabetic subjects are primarily related to the post-prandial metabolic responses generated by the food intake. This physiological glycemic variability is reproducible between two successive days under conditions of similar meals and activities. In insulin-treated diabetic patients, glycemic instability is directly related to loss of glucose homeostasis due to the failure then the deficiency of endogenous insulin secretion, but its physiopathological implication in term of diabetic angiopathy risk remains to be determined. Other exogenous glycemic instability factors are known and have to be corrected (not adapted repartition of the meals and/or the insulin doses during the day, inappropriate choices in insulin regimens, errors in insulin adjustments, inadequate insulin injection). Classical glycemic measurements used to appreciate the quality of the glycemic control do not provide or give partial and erroneous information on quality of glycemic stability. It's particularly the case for glycated hemoglobin and glycemic average. In order to exactly quantify glycemic variability, specific tools of measurement or calculation can evaluate the intra-day glycemic variations or excursions (MAGE), the day-to-day glycemic variations or excursions (MODD), the meal-related glycemic excursions (MIME) or the risk of severe hypoglycemia (LBGI). Some of these tools are easy to use, other much complex or difficult to apply in clinical practice, even by using new methods such as the continuous glucose monitoring system (CGMS). Thus, asymptomatic glycemic variability is related to loss of glucose homeostasis, but also to irrelevant or incompatibility of the treatments used to obtain glucose control in insulin-treated diabetic patients. The evaluation of glucose instability can be provided using new methods of glucose monitoring and could be useful to optimize the therapeutic regimens in some of these diabetic patients.