Glucose sensing issues for the artificial pancreas

The first retrospective continuous glucose monitor entered the market in 1999. Now that this tool gives online data, the question arises whether it is ready to be incorporated into a closed-loop system. The author discusses the following questions: (1) Is the accuracy of current continuous glucose monitoring (CGM) systems good enough for use in a prototype artificial pancreas system?; (2) How do we assess CGM accuracy?; (3) What is the minimal distance between a continuous glucose monitor and an insulin delivery site in which a CGM can function accurately?; and (4) Does any physiological and instrumental delay associated with continuous glucose monitoring hamper the development of an artificial pancreas?