What is a CGM? How it works and how to apply one

In an era where technology is involved in nearly every aspect of our lives, it’s no surprise that innovations are showing up in the health and wellness space too. 

From rings to watches to devices that track different aspects of our health and bodies, you've probably begun hearing about continuous glucose monitors (CGMs). While CGMs are not new technology — they have been around for well over a decade for those with type 1 and type 2 diabetes — more and more research is pointing towards the benefits of CGM technology for people without diabetes. ¹ 

So, what exactly is a CGM and how does it work? From where you put it on to how long it lasts, we’ll cover the basics in simple terms to better understand what adopting this technology actually means in real life.   

What is a CGM? 

A CGM is a small biowearable device, about the size of a quarter, that measures glucose levels in near real-time throughout the day and night.  

Unlike traditional blood glucose meters that require a fingerstick blood sample, CGM technology works via a tiny sensor inserted under the skin to continuously measure glucose levels in the interstitial fluid, which is a thin layer of fluid that surrounds your body’s cells. 

The sensor connects to a transmitter, which wirelessly sends data to a dedicated receiver or smartphone app.  

Compared with traditional blood glucose meters, a CGM measures glucose automatically (without the need for a blood sample) and as often as every 5 minutes. This generates more than 250 measurements per day, compared with individuals who use a glucose meter and rarely get more than seven measurements per day. ² 

The continuous and immediate feedback provided by a CGM can offer valuable insights into how your glucose levels respond to food, movement, medication, and other factors that impact metabolism such as sleep and stress. Instead of relying on spot measurements that only tell part of the story, a CGM provides actionable information that allows you to make informed decisions about your habits and lifestyle by tracking your glucose continuously, over time.   

CGMs not only allow you access to your glucose data in near real time, but you can also review the data over longer periods of time that you wear a sensor, such as a 24-hour period, week, or month at a time. This is useful to detect trends in your glucose levels and pinpoint what lifestyle factors are contributing to the values you’re seeing. 

Why use a CGM if you don’t have diabetes? Research suggests less glucose exposure is associated with greater metabolic health. ¹ And using a CGM and limiting glucose spikes can lead to several health benefits both in the short term and over time. ¹ 

How you apply a CGM 

Applying a CGM is a straightforward process that begins with preparing the site on your skin where you will apply the biosensor. Before application, it is best to clean the skin with an alcohol wipe to prevent any irritations or infections. 

Next, you will insert a sensor filament less than 0.4 millimeters (mm) in diameter, 5 mm under the surface of the skin with an easy-to-use applicator. 

Once the sensor is in place, you may need to attach a transmitter, although this depends on the brand of CGM you are using, as some transmitters are included with the sensor. The transmitter sends the data from the sensor to your phone or a receiver where you can view it. 

After the sensor and transmitter are in place, many devices require an activation, either by scanning the transmitter or indicating in the app that you’ve applied the sensor. The CGM will then begin to collect data. Most devices have a short warm-up period (around 30-60 minutes) before the real-time data will display on your phone or receiver. 

Where you can wear a CGM 

Two key advantages of CGMs are their compact design and the ability to wear them under clothing with minimal intrusion in your day-to-day life. They are designed to be discreet, so you barely notice you're wearing them. The most common placement locations include: 

• The back of the upper arm

• Your abdomen

• The upper buttocks area

These areas have enough fatty tissue to enable accurate readings. 

The CGM you're using will dictate the best location for placement. While some CGM sensors have received approval to give accurate readings from multiple site locations like the abdomen and buttocks, others only have approval for placement on the upper arm. 

It's best to check the package instructions to ensure you’re placing it in a location that will transmit accurate readings.

How long a CGM stays on 

How long you can wear a CGM will depend on the device and individual preference. Most CGMs are designed to stay in place for at least a week, while others can last as long as 90 days. ³ 

The adhesive patches that secure the sensor and transmitter to the skin are durable and water-resistant, ensuring they will stay attached during daily activities, including things like showering and exercise. 

Factors such as sweat, friction, and skin sensitivity may impact how long the adhesive lasts for each individual, however. Some users may find that the adhesive starts to peel off after a few days, while others may be able to keep them in place for the full life of the sensor.  

If you notice the adhesive peeling off sooner than you would like, it is important to not place any stickers, patches, or tape directly over the transmitter to avoid any issues with sending the sensor data to your receiver or smartphone. However, you may place tape or other patches to reinforce the edges of the adhesive, if needed. 

Many CGM companies and other third-party vendors offer customized patches that can easily fit over the sensor and transmitter to reinforce the adhesive without interfering with CGM readings.  

How long a CGM lasts

Check the package instructions of the CGM device you're using to learn how often you will need to replace the sensor. The most common CGMs on the market have the following wear times:  

• Freestyle Libre: 14 days 

• Lingo: 14 days 

• Dexcom G7: 10 days 

• Stelo by Dexcom: 15 days 

• Medtronic Guardian™: 7 days 

Over time, the sensor may gradually lose accuracy as it becomes exposed to fluids and undergoes natural wear and tear. To ensure reliable readings, CGM manufacturers recommend replacing the sensor at regular intervals specified by the device instructions. 

Many CGM receivers and smartphone apps will also automatically stop displaying data once the sensor has expired. By following the recommended replacement times, you can ensure you're always getting the most accurate readings.   

A final note from Lingo

CGMs are an established technology initially for diabetes patients that have now become increasingly popular among people looking to improve their overall health and well-being. From the simple application process to the insightful data, CGMs offer you a look into your unique glucose response to food, activity, and other lifestyle habits that can empower informed decisions about your health. 

Research shows that using CGMs like Lingo and limiting glucose spikes can have a positive impact on your overall metabolism and can help improve important aspects of daily life such as sleep, mood, energy, appetite, and focus, even if you don’t have diabetes. ¹ 

While each CGM system may have its own unique features and specifications, the overarching goal is the same: to enhance the quality of life for those wanting to dig deeper into their own metabolic health.  

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