A Continuous Glucose Monitor (CGM) is a medical device that tracks glucose levels throughout the day and night. The device works by inserting a tiny sensor wire just under the skin, where it measures glucose in the interstitial fluid, the liquid surrounding your cells. For the CGM to provide accurate readings and last its intended wear time, the physical location and method of application are extremely important. Incorrect placement can lead to unreliable data, device failure, or skin irritation, directly impacting glucose management effectiveness.
Officially Recommended Placement Sites
CGM manufacturers designate specific body areas for sensor placement based on rigorous clinical trials demonstrating accuracy and user safety. For the Abbott FreeStyle Libre systems, the sole approved site for adults is the back of the upper arm. This location is chosen because it offers a stable surface that minimizes movement and provides consistent subcutaneous fat tissue, which is necessary for the sensor wire. Dexcom systems, such as the G6, are officially approved for the abdomen and the back of the upper arm, while the newer G7 system is primarily recommended for the back of the upper arm. For younger children (ages 2 to 6), some manufacturers also approve the upper buttocks as a placement site.
Factors Guiding Optimal Site Selection
Selecting the exact spot within an approved region requires careful consideration to maintain sensor performance and skin health. It is necessary to rotate the insertion site with every new sensor, even if using the same general body area. Consistent re-use of the same small spot can lead to the formation of scar tissue or lipohypertrophy, which can disrupt the flow of interstitial fluid and cause inaccurate glucose readings.
When preparing the skin, users should choose an area that is at least one to three inches away from any insulin injection sites or pump infusion sets. The chosen spot must be smooth, avoiding moles, scars, stretch marks, tattoos, or bony prominences. These irregularities can interfere with the sensor’s function or cause discomfort during wear. Select a spot that is unlikely to be affected by clothing, such as avoiding the belt line or pocket areas, which could snag or compress the device.
A primary concern in site selection is preventing “compression lows,” which are false low glucose readings caused by sustained pressure on the sensor. This pressure, often from sleeping directly on the sensor, restricts the flow of interstitial fluid to the area. The resulting fluid reduction leads the sensor to report a falsely low glucose value, potentially triggering unnecessary alerts or treatment. To avoid this, side-sleepers should place the sensor on the arm or side they do not typically sleep on, and choose a flat area that avoids pressure points from clothing or furniture.
Navigating Alternative and Off-Label Placement Areas
Some users experiment with alternative body locations, such as the forearm, thigh, chest, or lower back, especially when approved sites become irritated or overused. These sites are considered “off-label” because manufacturers have not conducted clinical trials to validate their accuracy and safety for those specific areas. While some individuals report success, off-label sites carry specific risks that can affect performance, such as slower blood flow in the thigh or calf leading to delayed readings, or thinner tissue in the forearm being prone to dislodgement. If readings seem unusual or do not match physical symptoms, it is advisable to use a traditional fingerstick blood glucose meter to confirm the data and ensure reliable diabetes management decisions.