John B. Welsh, MD, PhD

The potential value of continuous monitoring of blood glucose and the enzyme-based electrode that underlies continuous glucose monitoring (CGM) in the subcutaneous tissue were described in the 1960s. In 1999, the FDA approved the first “professional” CGM system, which stored data over 3 days for later retrieval and analysis. However, many patients (even volunteers in CGM-based clinical trials) found early-generation systems uncomfortable and difficult to wear. By contrast, current systems are more accurate, provide customizable alerts and alarms, are easier to use and less likely to cause skin irritation, resist interference from acetaminophen, allow for real-time data to be shared and remotely monitored, and are stable enough so as not to require periodic calibrations with SMBG values.