Rather than measuring blood like a finger prick system, the 14 Day FreeStyle Libre sensor measures a thin layer of fluid that surrounds the cells of a tissue below the skin called interstitial fluid.
Because glucose in the blood takes time to make its way into the interstitial fluid, there might be some lag time between the FreeStyle Libre sensor reading and a blood prick reading. However, when blood glucose levels are stable, the FreeStyle Libre reading will be very similar to a blood glucose reading.