Perhaps the most innovative technology for the treatment of type 1 diabetes is the introduction of real-time continuous glucose sensors introduced in 2006 (figure 13). Retrospective 72-hour continuous glucose monitors (CGM) have been available since 1999. Both real-time and retrospective sensors measure interstitial fluid (ISF) glucose with glucose oxidase. A current is generated which is then transmitted to a receiver as a glucose measurement, which is in essence a mean ISF glucose value over the previous few minutes. Due to the time it takes to measure the glucose, there is a lag in the glucose reading when comparing blood glucose and CGM values. This is particularly relevant when glucose levels are trending up or down quickly. Due to this, these initial devices are labeled for use as adjunctive therapy with routine SMBG. Patients can customize alarms to activate for hypoglycemia or hyperglycemia. Understanding the trend allows patients to use another parameter to increase or decrease the mealtime insulin dose. It also allows patients to intercept hypoglycemia (or hyperglycemia) prior to its occurrence. As noted in figure 13, one sensor is integrated with an insulin pump (a “sensor-augmented pump”) so that the pump and receiver is the same device. Even after short periods of time, many patients can learn how to best use this technology to improve both mean glucose and glycemic variability (figure 14).
Figure 13. Examples of real-time continuous glucose monitoring systems. Left: the Medtronic MiniMed Sensor Augmented Pump (top shows patient wearing it, bottom shows schematic of concept). Center: the DexCom STS continuous glucose sensor (top shows patient wearing it, bottom shows receiver). Right: Abbott Diabetes Care Navigator continuous glucose sensor (top shows patient wearing it, bottom shows receiver).
Figure 14. Example of a download from a patient using a sensor-augmented pump showing (upper) first week on device and (lower) improved control during second week on the device.
It would be a mistake to consider these first-generation glucose sensors as a final chapter in the improvements in technology of type 1 diabetes. Rather, this is actually a beginning of much more sophisticated technology which should in the future lead to a true artificial pancreas.