Glucose levels can be measured from the bloodstream, or from the interstitial fluid (ISF), which surrounds the body’s cells. There is a 5- to 10-minute delay in ISF glucose response to changes in blood glucose,²³⁶ which is unlikely to impact routine day-to-day treatment decisions. The average lag time of the FreeStyle Libre system is approximately 5 minutes.²³⁷

ISF glucose and BG measurements taken simultaneously won’t always match, and are likely to be different.