Continuous glucose monitors: the pedometer for diabetic glucose monitoring
Continuous glucose monitoring systems (CGMS) provide users 24/7 blood glucose monitoring. The available systems include three devices: a disposable sensor which is stuck to the body and takes subcutaneous blood glucose readings, a reusable transmitter which relays sensor readings to a monitor, and a wireless monitor which offers real-time readings. Sensor working-life ranges from three days (Medtronic systems) to seven days (DexCom STS). Nevertheless, most diabetics who use CGMS will wear sensors beyond the approved life of the disposable. Extended non-approved wear of sensors can lead to improper readings and place patients at risk. In response, companies have begun adding new features that will limit improper sensor usage. On a basic level, CGMS gives users:
• Blood glucose readings as often as every 1-2 minutes (up to 288 readings per day)
• Are capable of showing trends and charts over various time frames
• Have alarms to inform users at risk of becoming hyper – or hypoglycemic.
CGMS technology is still being developed and labeling (and performance) has some room for improvement. CGM systems are indicated for use as an adjunct to conventional blood glucose monitoring. The technology is still fairly new, and though it is FDA-approved, results are dependent on users properly calibrating the device based on values drawn from finger-sticks. The variance between CGMS readings and actual blood glucose levels can be as great as 20%. However, we expect continued improvement with future generations of devices. If the system is well calibrated and used appropriately, the trending data for glucose levels throughout the day can be a valuable indictor for diabetics in gaining added insight into blood glucose levels that exist outside of the recommended ranges. Though most insulin dependent diabetics are able to manage their disease very well, they may be unaware of the extreme peaks and valleys since SMBG only offers results for fixed points in time. While SMBG typically is done only three times a day, CGMS can provide up to 288 glucose readings per day depending on the device. With the overall goal being the maintenance of a healthy overall A1C level, CGMS gives diabetics the opportunity to regulate their disease on a more real-time basis to better control their glycemic variability.
The American Diabetes Association (ADA) is beginning to recognize the importance of continuous monitoring in type 1 diabetics. This shift at the ADA was facilitated by results from the Juvenile Diabetes Research Foundation (JDRF) trial which confirmed utilization of CGM technology helped in reducing A1C levels in certain patients. The 2009 ADA guidelines were updated to include the following language:
• CGM in conjunction with intensive insulin regimens can be a useful tool to lower A1C in selected adults (aged 25 years) with type 1 diabetes
• Although the evidence for A1C lowering is less strong in children, teens, and younger adults, CGM may be helpful in these groups. Success correlates with adherence to ongoing use of the device
• CGM may be a supplemental tool to SMBG in those with hypoglycemia unawareness and/or frequent hypoglycemic episodes