The interstitial fluid, a small layer of fluid that surrounds the tissue cells beneath your skin, is used to acquire CGM sensor data. Glucose enters your bloodstream before it is absorbed into the interstitial fluid as carbs are digested. This is why a blood glucose test may give you a different result than an interstitial fluid scan. Sensor measurements eventually catch up to blood glucose readings, providing you with a more comprehensive view of your levels rather than just a snapshot in time.