A continuous glucose monitor (CGM) is a small, sophisticated device that provides real-time information about glucose levels without the need for frequent finger sticks. The sensor filament, inserted just beneath the skin, measures the concentration of glucose in the interstitial fluid, the liquid that surrounds the body’s cells. Because the sensor is not measuring blood directly, its precise location significantly affects the accuracy and consistency of the readings. Proper placement is paramount to ensure the data is reliable for making daily health decisions and to maximize user comfort throughout the sensor’s wear time.
Approved Placement Zones
The primary locations approved for CGM sensor placement are those areas of the body that offer a consistent layer of subcutaneous fat to house the filament. For most adults, the two main manufacturer-approved sites are the back of the upper arm and the abdomen. Research indicates that the accuracy of readings between these two sites is generally comparable.
The back of the upper arm, specifically the triceps area, is often preferred because it is a location with relatively low movement and good subcutaneous tissue. This site is also discreet and less likely to be dislodged by clothing or daily activities. When using the abdomen, the sensor should be placed in the fatty tissue at least two inches away from the navel to avoid areas where underlying muscle tissue is closer to the skin surface.
Placement rules can differ for specific devices and age groups, requiring review of the product instructions. For instance, some manufacturers approve the upper buttocks as an alternative site for children between the ages of two and seventeen. This location is often chosen for highly active individuals because it offers a large, stable area that is less prone to accidental bumps or movement-related sensor failure.
Preparing the Skin and Site Rotation
Before applying a new sensor, careful skin preparation is necessary to ensure the adhesive forms a secure, hygienic bond. The selected site must first be cleaned thoroughly, typically with an alcohol wipe, to remove surface oils, dirt, or lotions. It is important to let the area dry completely before insertion, as a damp surface will compromise the adhesive’s ability to stick.
Once the sensor’s wear period is complete, site rotation is mandatory for long-term skin health and sensor function. Rotation ensures the skin is not subjected to continuous adhesive use or repeated micro-trauma from the sensor filament. Repeatedly inserting a sensor into the exact same location can lead to the formation of scar tissue, or lipodystrophy, beneath the skin.
This hardened tissue has compromised blood flow and interstitial fluid exchange, which can reduce the accuracy of the CGM’s readings. Users should avoid simply alternating between the left and right sides and instead move the insertion site a minimum of one to two inches away from the previous spot within the approved zone. Systematic rotation allows the skin and underlying tissue to fully heal before a sensor is placed there again.
Optimizing Placement for Accuracy and Comfort
Selecting the precise spot within an approved zone requires considering anatomical and lifestyle factors to maximize accuracy and comfort. The sensor must be placed in an area with sufficient subcutaneous fat, as this tissue is rich in the interstitial fluid the device measures. Placement over bony areas, muscle, scar tissue, or stretch marks should be avoided, as these locations interfere with proper sensor function.
One common issue affecting sensor performance is a “compression low,” which occurs when sustained pressure is applied directly to the sensor. This pressure, often from lying on the sensor during sleep, temporarily compresses the tissue and reduces the volume of interstitial fluid available. The resulting false low reading can trigger alarms and lead to incorrect treatment decisions.
To avoid compression lows, place the sensor on a side of the body the user typically does not sleep on. Users should also avoid placing the sensor near the belt line, waistbands, or other locations where clothing might cause constant friction or pressure. For highly active individuals or those with adhesion difficulty, supplemental products such as skin barrier wipes or specialized overlay patches can reinforce the adhesive, providing security against accidental dislodgement.