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.