There’s no need to use a separate blood glucose meter for routine testing. 1 The app allows you to get glucose results as often as you like by simply scanning your FreeStyle Libre sensor with your phone.  However, a finger prick test using a blood glucose meter is required during times of rapidly changing glucose levels when interstitial fluid glucose levels may not accurately reflect blood glucose levels, if hypoglycaemia or impending hypoglycaemia is reported by the Sensor, or when symptoms do not match the Sensor readings.

Reference:

1. FreeStyle Libre flash glucose monitoring system User manual.