A Continuous Glucose Monitor (CGM) is a compact, wearable technology that provides continuous, real-time tracking of glucose levels. Unlike a traditional fingerstick test that offers a single snapshot, the CGM measures glucose in the interstitial fluid. This small sensor component, inserted just under the skin, relays data via a transmitter to a receiver or smartphone. Accurate sensor placement is paramount because the device must access the interstitial fluid reliably to provide readings that closely reflect blood glucose trends. The location chosen directly influences comfort, adhesion, and the reliability of the data used for health management decisions.
Manufacturer-Approved Body Sites
The placement of a Continuous Glucose Monitor is subject to specific regulatory approval. The two most commonly approved locations are the back of the upper arm and the abdomen. These sites are chosen because they contain a sufficient layer of subcutaneous fat, where the sensor filament resides to measure glucose in the interstitial fluid. They also tend to be areas with less muscle movement, which helps stabilize the sensor and prevent inaccurate readings.
For devices approved for the back of the upper arm, the sensor is typically placed on the posterior aspect, where the skin is relatively flat and less prone to snagging. The abdomen is also a frequent site, often specified as being at least two inches away from the navel and other injection sites. For children aged two to seventeen, some manufacturers also approve the upper buttocks. Users must consult the specific device instructions, as approved sites vary between systems. Using a site not officially approved is considered “off-label” and may compromise data accuracy or warranty.
Practical Steps for Application
Applying a CGM sensor begins with skin preparation. The selected site should be washed with non-moisturizing, fragrance-free soap and then cleaned with an alcohol wipe. Let the area dry completely for at least ten seconds before proceeding, as residual moisture or oil can interfere with the adhesive’s ability to bond securely. If the site has a lot of hair, it should be trimmed or shaved to ensure maximum adhesion.
The sensor is inserted using a specialized, often single-use applicator, which automates the process. The user firmly places the applicator against the prepared skin and presses a button or pushes down to trigger the insertion. This mechanism uses a needle to quickly pierce the skin, but the needle retracts immediately, leaving only a flexible sensor filament beneath the skin’s surface. After insertion, the applicator is removed, and the sensor housing is gently pressed to secure the adhesive patch. The final step is to activate the sensor, typically through a smartphone app or a dedicated receiver, which initiates a warm-up period before glucose data begins to appear.
Factors for Optimal CGM Placement
Site rotation involves moving the sensor location with each replacement to allow the skin to heal and prevent scar tissue buildup. Repeated use of the exact same spot can lead to inflammation and altered tissue structure, which may affect the sensor’s accuracy. A common rotation strategy involves alternating between the left and right sides of the body and different quadrants within the same general area, such as the abdomen.
Users should avoid placing the sensor over certain areas to maximize accuracy and comfort. These areas include:
- Scars.
- Stretch marks.
- Moles.
- Large veins.
- Any site with existing skin irritation or rashes.
The sensor must also be placed at least three inches away from any recent insulin injection or pump infusion sites to prevent interference with the glucose readings. Bony areas or sites with very little fat tissue should also be avoided, as they can cause discomfort and lead to less stable readings.
Avoiding pressure points helps prevent “compression lows.” A compression low is a false low glucose reading that occurs when sustained pressure is applied directly to the sensor, often while sleeping or leaning against a surface. This pressure temporarily restricts the flow of interstitial fluid, causing the sensor to report an inaccurately low reading. To mitigate this, users should choose sites that are unlikely to be laid upon or tightly compressed by clothing, belts, or seatbelts. For active individuals, selecting a site on the torso or a more protected area of the arm can minimize the risk of the sensor being accidentally bumped or snagged during exercise or daily activities.