Using a continuous glucose monitor (CGM) can help you catch spikes and dips you may have missed between tests with your meter. And with the data downloaded from your device, you can use trends to better manage your diabetes.

So, what is a CGM? The device uses a sensor to measure glucose levels in the fluid just under the skin (very similar to glucose levels in the blood). The sensor transmits the results to a handheld receiver or insulin pump every few minutes, so you know what your glucose levels are throughout the day. Depending on the CGM you choose, you’ll wear the sensor for three to seven days before replacing it. You’ll insert the sensor much like an infusion set for an insulin pump, with a handheld applicator and special adhesive tape.

There are four CGMs on the market today, and while they differ a bit—one has a built-in blood glucose meter; another doubles as an insulin pump—some key functions are available on each, as described below.

Before you purchase a CGM, talk with your insurance company, since some cover only a specific brand. Many insurance companies won’t cover CGMs for people with type 2 diabetes, so it’s important to ask. If your doctor or diabetes educator has sample products available, take the opportunity to play around and get a feel for the system. Once you’re ready to buy, a representative from the device company will guide you through the process.

Choosing a CGM is personal, and what works for someone else may not be right for you. Some people don’t like carrying an extra device (and dealing with the sensors) while others find that constant glucose monitoring keeps their diabetes in check. That’s why it’s important to know your options. From there, consider the bells and whistles until you find a device that suits your needs.

Functions to Consider
Continuous Readings
While the different models vary on how often they send glucose readings to the receiver (one transmits every minute while another does every five; the difference is too slight to matter, experts say), they all do it often enough to give you a clear picture of your glucose 24-7.

Glucose Direction
Your blood glucose is 90 mg/dl. But are you stable, heading up, or dropping? Along with your current reading, your CGM’s home screen will use arrows to reveal how yourglucose level is trending.

Trend Graphs
With the push of a few buttons, you can view your glucose levels in graph form. Track your glucose over the past hour, six hours, or 24 hours. Doing so will help you spot trends (say, that nighttime low you never picked up while using a meter) and act on them.

Event Markers
Last week’s glucose graph may show extra low readings, but do you know what caused them? If you mark an event—like the fact that you exercised a lot—you’ll have a better idea of why your glucose levels behaved the way they did.

Safety Alarms
To help you catch high or low glucose even if you’re not staring at your screen, your CGM will sound an alarm. Each model lets you program high and low glucose alarms, which sound if you hit your customized limits. Some alert you if your glucose is rising or falling too fast, or if you’re approaching preset upper or lower glucose limits.

Calibration
To make sure your CGM is functioning properly, you’ll need to calibrate it by testing your blood glucose with a meter and putting the results into your CGM. How often you’ll have to calibrate (and suspend the CGM function) varies with the particular device.

Updated Jan. 4, 2011