A continuous glucose monitor (CGM) automatically tracks glucose levels throughout the day and night. This device provides a more complete picture of glucose trends compared to a traditional fingerstick test, which only offers a single data point in time. The CGM sensor, featuring a small filament, is inserted just under the skin to measure glucose in the interstitial fluid, which is the fluid surrounding the body’s cells. Using a CGM provides real-time information that helps individuals make more informed decisions about diet, physical activity, and medication. This guide will walk through the practical steps of applying the sensor, activating the device, and understanding the valuable data it provides for daily health management.
Site Selection and Sensor Application
Correct placement of the sensor is the first step toward ensuring accurate readings and comfortable wear. Most manufacturers approve the back of the upper arm or the abdomen as suitable sites, though specific recommendations vary between device models. Choose a flat area with adequate subcutaneous fat, avoiding sites that have scars, tattoos, irritation, or are prone to being bumped or compressed during sleep. Ensure the chosen location is at least three inches away from any insulin injection or infusion pump sites.
Before application, the selected skin area must be thoroughly cleaned with an alcohol wipe to remove any natural oils or residue, and then allowed to air dry completely. This maximizes the adhesive’s effectiveness and minimizes the risk of infection. The sensor is typically inserted using an applicator, which is a simple, spring-loaded device that places the filament just below the skin’s surface with minimal sensation.
After the applicator is pressed firmly against the skin and the insertion button is activated, the sensor base will be securely attached by its adhesive. Some systems require the user to snap a separate transmitter into the sensor base, while others have the transmitter integrated into the disposable sensor unit. Following insertion, gently rubbing around the adhesive patch helps to ensure a secure seal that can withstand daily activities. Rotating the application site for each new sensor reduces the chance of developing scar tissue or localized irritation.
Device Activation and Initial Warm-up
Once the sensor is physically attached, the next step is to activate it, which initiates the connection between the sensor and the reading device, typically a dedicated receiver or a smartphone application. The activation process usually involves entering a unique sensor code found on the packaging into the app or receiver, or simply scanning the newly applied sensor. This step pairs the two components and allows the system to begin collecting and transmitting data.
Following activation, every CGM system requires a “warm-up” period before it can display any glucose readings. This time, which can range from 30 minutes up to two hours depending on the brand, is necessary for the sensor filament to equilibrate within the interstitial fluid of the body. The sensor uses this time to acclimate to the tissue environment and calibrate its electrochemical measurements to provide accurate data. No glucose readings are available until this warm-up is successfully completed.
Understanding Glucose Data and Trends
The primary benefit of a CGM is its ability to provide dynamic information, which is far more useful than a single static glucose number. The display shows the current glucose reading alongside a trend arrow, which indicates the direction and rate at which the glucose level is changing. Understanding these trend arrows is a fundamental aspect of using the device, as they enable proactive management decisions.
Trend Arrows
- A single arrow pointing straight up or down signals a rapid change, often 60 to 90 mg/dL within 30 minutes.
- A diagonal arrow indicates a slower, more gradual change of about 30 to 60 mg/dL in the same time frame.
- A straight horizontal arrow means the glucose level is relatively stable.
- Double arrows pointing up or down warn of a very fast, steep change, sometimes exceeding 90 mg/dL in 30 minutes, requiring immediate attention.
Beyond the immediate number and arrow, the device’s software allows users to review historical data, typically presented as a graph showing glucose fluctuations over several hours or days. Analyzing these graphs helps identify patterns, such as consistent spikes after certain meals or dips during a specific time of day, like overnight or after exercise. This retrospective analysis is what allows users and healthcare providers to fine-tune treatment plans and lifestyle choices.
A significant metric for long-term management is Time in Range (TIR), which measures the percentage of time a person’s glucose level remains within a predetermined target range, commonly set between 70 and 180 mg/dL. TIR offers a more complete picture of glucose control than a single A1C value, which only provides an average. The goal for most people is to achieve a TIR of 70% or more, which has been shown to correlate with a lower risk of complications.
Sensor Care and Replacement
Daily care of the sensor focuses on protecting the adhesive patch and the device itself from physical dislodgement or damage. The sensor is water-resistant, allowing for showering, swimming, and exercise, but prolonged immersion, typically beyond 30 minutes, should be avoided. Be careful when drying off with a towel or dressing to avoid snagging the sensor on clothing, which can pull it off prematurely. Some users apply an overpatch or medical tape around the adhesive for extra security, especially during activities that involve heavy sweating or contact.
If the sensor falls off before its designated wear period is complete, it cannot be reinserted or reused, and a new sensor must be applied. When the sensor reaches the end of its lifespan, often 10 to 14 days, the application will notify the user that it is time for replacement. To remove the old sensor, gently peel the adhesive away from the skin, often using an adhesive remover wipe or baby oil to help loosen the edges. After removal, select a completely new site for the next sensor to promote skin health.