Introduction to your CGM: Get the Facts on Continuous Glucose Monitors

If you’ve been diagnosed with type 2 diabetes, you have had to learn a whole new vocabulary — A1C, blood sugar, glucose, insulin, test strips, and more. You may have even heard the term continuous glucose monitor, or CGM.
Continuous Glucose Monitoring systems (CGMs) offer an advanced way to check glucose readings in real-time or monitor glucose readings over time to see trends.  Seeing glucose levels continuously helps a person living with type 2 diabetes make informed decisions about balancing food, activity and medicines.


What is a CGM?

A continuous glucose monitor, or CGM for short, is a compact medical device that monitors your glucose levels every five minutes.  It can be a really powerful tool for people with type 2 diabetes because you can see how food, sleep, stress and movement affect your glucose levels – without fingersticks, guesswork, or frequent doctor visits.


How do CGMs Work?

To use a CGM, you insert a small sensor onto a spot on your body, such as your stomach. A miniscule cannula, almost like a tiny straw, inserts under the skin. Adhesive holds the sensor in place, usually for a period of up to 10 days; we recommend that you replace the sensor every 10 days, regardless. When inserted, the sensor takes glucose readings from fluid in the skin (called interstitial fluid).
A small, reusable transmitter attaches to the sensor to wirelessly transmit your glucose reading to a receiver. For many CGM systems, your smart phone acts as the receiver. This makes it easy to use — checking your blood sugar is as simple as opening an app on your phone.
CGMs are virtually painless to apply, discreet, and are water-resistant.  You can shower and work out without issue.


Why Monitor Blood Glucose Continuously?

Traditional glucose monitoring can be challenging.  Blood glucose meters (BGM) require drawing blood with a finger prick.  This process involves time, carrying testing equipment and discomfort.  Intensive monitoring may involve checking blood sugar four or more times per day, and generally only during waking hours.  Unlike BGM, which require deliberate action to get a reading, CGM systems provide dynamic real-time information about the direction of glucose levels and rate of change. This proactive approach is not possible with BGMs.
A new CGM glucose reading is received every 5 minutes, around the clock.  That’s up to 288 sensor glucose readings every 24 hours, filling in the gaps that existed between meter checks.  Because readings are frequent, it is possible to track the trend of rising or falling glucose levels.  These readings are plotted on a graph, called a CGM trend graph.  Colored areas on the display on the left indicate at a glance whether glucose is in the normal range (grey), too high (yellow) or too low (red).
The direction of glucose change is indicated by an arrow next to the glucose reading called a trend arrow.  A level arrow means glucose is stable.  An arrow pointing upward indicates glucose is rising, and an arrow pointing downward shows glucose is dropping.  The more vertical the angle of the arrow, the faster the glucose level is changing.

How is a CGM Used?

The Dexcom G6 CGM is approved for home use for children and non-pregnant adults.  The G6 sensor is FDA approved for wear on abdomen only.  This CGM has not been studied for accuracy in any other body location and is not guaranteed to read accurately except on the abdomen. The sensor may be inserted by the user.  It is not necessary to have a medical professional do this.
The CGM sensor filament is very comfortable and rarely felt in the skin. According to a survey of Dexcom G6 users, 84 percent reported that the initial sensor insertion was painless and 100 percent reported that the applicator was easy to use.  All CGM systems require a “warm-up” period before displaying glucose readings.  The warm-up period for Dexcom G6 is two hours.  In order to view your glucose readings, you will need to keep your receiver or smart device within 20 to 30 feet (in the same room).  This is to prevent loss of Bluetooth communication between the sensor and the receiver.  If communication between these components is lost or blocked for longer than 10 minutes, there will be gaps in the glucose readings and the trend graph that you see on your app.

Is CGM Data Accurate?

The most accurate glucose measurement is a blood test drawn from a vein at your doctor’s office.
Both meters and CGM are compared to that doctor’s test to measure accuracy in clinical studies. They aren’t compared to each other. Because of this, the CGM reading and meter value are unlikely to be the same number, but they should be close.  If your CGM reading is within 20 percent above or below your meter value, they match closely.
The top six most accurate BGMs have about 15 percent error, but less accurate models can have a 20 percent error, with considerable differences between brands and quality. Storage environment and expiration of strips also greatly affect test strip accuracy.  CGMs have an error range of 8 to 9.5 percent.  The FDA has approved the Dexcom CGM as accurate enough to be used to calculate correction doses of insulin without a confirmatory BGM reading.  CGMs have lowest accuracy (but still an approved level) in the first 12 -24 hrs of the session.  Some users feel calibrating with their BGM once during this period improves initial accuracy.  Calibrating the CGM when readings are within acceptable error range, or calibrating frequently, can disrupt the glucose calculation algorithm and can lead to worsened accuracy overall.  Users who receive consistent G6 readings outside of the +/- 20% range from their BGM should visit the Level2 Support Section about Dexcom CGMs.


CGMs are Game-changers

Continuous glucose monitoring is empowering. It’s been said that fingersticks are like seeing a photograph and a CGM is like watching the movie. With the movie, you get the full story of your diabetes each day. And the story of your glucose levels is likely far more interesting and informative than you’d expect.
For example, you may see that the “healthy” snack you’ve been eating is actually causing a big glucose spike. You might notice that stress causes spikes and a good night’s sleep contributes to steady glucose levels. Maybe that walk you’ve been adding to your morning routine is really making a difference.
It can be informative to see what’s leading to spikes and rewarding to see what’s keeping you steady. In fact, studies show that the act of wearing a CGM alone can help people with type 2 diabetes lower their A1C. It also helps people obtain optimal Time in Range.
In other words, with a CGM, you can see that small changes you’re making for your health are having a big impact.

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