Using a Continuous Glucose Monitor (CGM) can be a game-changer for managing Type 1 Diabetes, but it’s important to understand what can affect its accuracy to avoid frustration or dangerous mistakes. Many people don’t realize that CGMs don’t measure glucose directly in the bloodstream, but rather in the interstitial fluid surrounding the cells. This inherent delay means rapid changes in blood sugar, whether spikes after meals, drops during exercise, or hypoglycemic events, can show up 5 to 20 minutes later on the CGM than a fingerstick test. Knowing this, it’s wise to confirm any drastic or unexpected readings with a traditional blood glucose test before making critical insulin dosing decisions. Sensor warm-up is another key factor that users often overlook. Even when the device’s timer ends, the sensor needs extra hours—typically 12 to 24—to stabilize, as early readings can run higher or lower than actual blood sugar. Adhesive swelling on the skin can also interfere, causing distorted signals. Positioning your sensor matters too: areas with steady movement and minimal pressure like the outer upper arm or thigh usually provide better accuracy than places like the back of the arm or stomach, which are subject to motion or pressure. Avoid tight clothing or leaning on the sensor to prevent false low alerts caused by compression. Hydration status plays a significant role as well. When you are dehydrated, there is less fluid in your tissues which slows and dampens the glucose signal, causing flat or frozen trends on your CGM. Staying well-hydrated helps improve sensor response and reliability. Be mindful of medications and skin conditions that might interfere with readings. For example, high doses of acetaminophen, especially on older Dexcom models, and severe skin irritation or scar tissue can cause false highs or erratic data. Faulty sensors occasionally happen and are not your fault; if you experience consistent discrepancies by 40 to 80 mg/dL or noisy signals, contacting your supplier for a replacement is recommended. Ultimately, CGMs are excellent tools that tell your glucose story through trends rather than pinpoint exact numbers. Listening to your body in combination with verifying unexpected readings via fingersticks helps you make safer, informed decisions. By understanding these hidden factors affecting CGM accuracy, you can navigate highs and lows more confidently and better control your blood sugar management.