Continuous glucose monitoring: physiological and technological challenges.

Over the past decade, several continuous glucose monitoring systems have been developed, representing remarkable technological achievements. Most of the systems monitor glucose invasively in the subcutaneous tissue. It is important to realize that there are discrepancies between blood and interstitial glucose concentration, which (1) may impact the quality of the system calibration and thereby the accuracy of the data, (2) may jeopardize the specificity and the sensitivity of hypoglycaemic alarms based on these systems and (3) must be considered in the design of closed-loop insulin delivery systems. The aim of this review is to make the point that the challenge of developing a continuous glucose monitoring system is not only technological, but must also take into account the physiology of glucose in alternate sites where it is sensed.