Objective: Can Continuous Glucose Monitoring (CGM) systems predict capillary glucose levels < 0.80g/L Research Design and Methods: During their education to the use of CGMS, thirty-three patients with Type 1 Diabetes (T1D) collected 386 observations that included: the trending arrow, the Interstitial and the Capillary Glucose Level (IGL and CGL), at time 0 and 15 minutes later, without any intervention. 

Results: Initial descending arrows preceded decreasing CGL: -0.15 ± 0.28g/L vs -0.01 ± 0.23g/L if stable and +0.02 ± 0.23g/L if ascending arrow, p=0.008. For the 222 observations with correct initial IGL (0.80-1.60g/L), a final CGL lower than 0.80g/L was observed in 31% of cases after a descending arrow, 10% after a stable arrow and never after an ascending arrow (p<0.0001). 

Conclusion: When the Interstitial Glucose Level is correct, the trending arrow of the CGMS predicts the risk of hypoglycaemia 15 minutes later, but there is a large room for improvement of its accuracy.