Even with regular blood glucose monitoring, one of the big unknowns in diabetes self-management is what happens to glucose levels between blood glucose checks. In recent years, however, the development of continuous glucose monitors that check glucose levels in the fluid just under the skin have started to change all that. The newest continuous glucose monitors measure glucose levels continually around the clock and display results every few minutes.
The first continuous glucose monitoring systems simply collected data, which had to be uploaded to a computer for analysis. When the numbers were plotted on a graph, it became possible to see, for example, whether glucose levels were rising after meals or getting too low overnight.
The newer systems display glucose readings on a screen, so the user can see, in real time, what his glucose level is and whether it is rising or falling. The newer systems can also be programmed to sound an alarm when the user’s glucose reaches high or low levels. Some systems are able to display graphs showing glucose levels over a certain number of hours on the display screen. And the data collected by all the systems can still be uploaded to a computer for graphing and analysis, if desired. (See “Devices on the Market” to learn more about currently available continuous glucose monitoring systems.)
For all the information they provide, however, continuous monitoring devices do not replace regular blood glucose monitoring. Continuous monitoring systems must be periodically calibrated with conventional blood glucose meters using fingerstick blood samples for accurate readings. In addition, users are advised to do a conventional blood glucose check before making any changes in their diabetes care regimen.
How glucose sensors work
The glucose sensors used in continuous glucose monitors are small electrodes that the user places under the skin using an introducer needle and a spring insertion device that is similar to a lancing device or insulin pump infusion set inserter. Once the sensor is inserted, the introducer needle is removed, and only the sensor remains under the skin, held in place with an adhesive patch. The sensor must be changed every few days, according to the manufacturer’s recommendation. Inserting a glucose sensor should not be painful, and wearing a sensor should be comfortable.
The sensor produces a very small electrical current based on the amount of glucose in the body fluid (called interstitial fluid) around the sensor. When the glucose level rises, the current rises. When the glucose level goes down, the current goes down.
The sensors presently on the market need a number of hours to settle in to the body before they can start giving accurate glucose information. When the sensor is ready, the user calibrates the device by doing a fingerstick blood glucose reading and inputting the reading into the device (different systems have different methods for inputting information). The continuous monitoring device uses the reading to determine what the measured electrical current means in terms of glucose concentration. Additional calibrations are performed while wearing the sensor, according to the manufacturer’s recommendations.
To get the most accurate readings from a continuous glucose monitor, it is important to calibrate carefully and correctly. You must use your best blood glucose monitoring technique, including checking on clean, dry fingers, using strips that have been stored properly, and coding and using your meter correctly. Remember: The sensor glucose information you get is only as accurate as the quality of the calibration you do.