A Continuous Glucose Monitor (CGM) is a medical device that tracks glucose concentrations in the interstitial fluid, the fluid surrounding cells beneath the skin. This technology provides a comprehensive view of how diet, exercise, and medication affect glucose levels throughout the day and night. Successfully applying the sensor is the first step toward utilizing this data for better glucose management, as the device must be correctly positioned to function. The application process involves straightforward steps, from proper site preparation to the final digital activation.
Preparation and Choosing the Application Site
Before beginning, gather all necessary supplies, including the new sensor pack, the applicator, and an alcohol wipe provided in the kit. Users should check the expiration date printed on the sensor box to ensure the device’s accuracy before application. Preparing the skin beforehand is important for ensuring the adhesive remains secure for the entire wear period.
The selection of the application site impacts both comfort and sensor function. Many CGMs are designed for placement on the back of the upper arm, though some models may be approved for the abdomen or upper buttocks. A good site has adequate subcutaneous fat, allowing the small sensor filament to rest in the interstitial fluid without hitting underlying muscle or bone.
Site rotation is required to maintain skin health and prevent localized irritation or scar tissue development. Users should avoid applying a new sensor to the exact same spot previously used, ideally resting a site for at least a week before re-use. The chosen area should also be kept away from the waistband, scar tissue, tattoos, or areas prone to being bumped or pressed, which could dislodge the sensor.
Once the site is chosen, clean it thoroughly with an alcohol wipe to remove oils, lotions, or residue that could interfere with the adhesive. The skin must be allowed to dry completely before proceeding with the sensor application. Moisture prevents the adhesive from forming a strong bond, which could lead to the sensor detaching prematurely.
Detailed Steps for Sensor Insertion
The next phase involves assembling the components and performing the physical insertion. Depending on the device, this may involve twisting the sensor pack and the applicator together until they click, or removing a cap from an integrated applicator. Users should confirm that any alignment marks are lined up correctly. Keep the components sterile by avoiding contact with the sensor filament or the adhesive backing.
Once the applicator is prepared, hold it firmly against the cleaned and dried application site. Create even, stable contact between the adhesive patch and the skin surface to maximize adherence. Ensure the applicator is held perpendicular to the skin to facilitate a smooth, straight insertion of the sensor filament. Applying gentle counter-pressure to the surrounding skin can help stabilize the area before activation.
Insert the sensor by pressing a button or plunger on the applicator. This action releases a spring-loaded mechanism that rapidly inserts a thin, flexible sensor filament beneath the skin. The insertion needle retracts immediately back into the housing, leaving only the filament in the subcutaneous tissue to measure glucose levels. The speed of the insertion minimizes sensation, typically feeling like a quick pinch or light pressure.
After the click, gently pull the applicator straight away from the skin, leaving the sensor and its adhesive patch securely in place. Inspect the site to confirm the sensor is flush against the skin, and rub around the perimeter of the adhesive to ensure a strong seal. Observing a tiny drop of blood or feeling a slight, temporary sting is normal, as this is a common reaction to minor tissue trauma.
If the adhesive appears loose, the device is tilted, or the sensor is not seated correctly, the entire unit must be removed. Apply a new sensor to a different, newly prepared site. Following successful insertion, some users apply an over-patch—a secondary adhesive cover—to provide additional protection and keep the sensor secure during daily activities like exercise or bathing. These patches withstand moisture and friction, extending the sensor’s functional life.
Activating the CGM and Warm-Up Period
With the sensor attached, the final step is to establish a digital connection between the sensor and the display device, usually a dedicated receiver or smartphone application. Open the app or receiver and select the option to “Start New Sensor” or “Activate Sensor.” This process requires the display device to be held near the newly applied sensor for a few seconds to complete the pairing via near-field communication or Bluetooth.
The system will then prompt the beginning of a mandatory “warm-up period,” a programmed delay before readings become available. This waiting time is necessary for the sensor filament to settle within the interstitial fluid and for the sensor’s internal chemistry to stabilize. The sensor’s initial signal is often unreliable due to minor insertion trauma and the time required for the filament to become fully saturated.
During this warm-up phase, which ranges from 30 minutes to two hours depending on the model, the device will not provide glucose readings. Rely on traditional fingerstick monitoring during this time if immediate glucose data is needed for treatment decisions. Once the warm-up concludes, the display device usually issues an alert, and the first interstitial glucose reading appears, confirming the sensor is functioning correctly.