Several new CGM-derived parameters may provide additional insights into glycaemic control in T1DM, such as time in range (TIR) and parameters of glycaemic variability (GV). This study examined the interrelation and interpretation of these promising parameters.
The CGM device (seven days) provided following parameters: TIR (70-180 mg/dl), time in hypoglycaemia (total(<70);level 2(<55)) and hyperglycaemia (total(>180);level 2(>250)) and coefficient of variation (SD/mean glucose).
Patients (n=95; 45±10years; HbAc1:7.67±0.75%) were labeled as having good (HbA1c<7%;n=19), moderate (7-8%;n=46) or poor glycaemic control (HbA1c>8%;n=30). TIR was negatively associated with HbA1c (r=-0.508), MBG (r=-0.851) and time in hyperglycaemia (total:r=-0.924;level 2:r=-0.855), but not hypoglycaemia. However, TIR did associate with shorter time in level 2 hypoglycaemia in patients with good (r=-0.596) and moderate (r=-0.252) control. In contrast, COV was strongly positively associated with time in hypoglycaemia (total:r=0.750;level 2:r=0.740) but not with hyperglycaemia time. Once more, subgroup analysis showed that COV did correlate with time in hyperglycaemia in the lowest HbA1c group (total:r=0.588;level 2:r=0.662). Regarding the relationship between TIR and COV, TIR did not correlate with COV in the whole group but was negatively associated with COV in patients with good (r=-0.832) and moderate (r=-0.469) control.
This study provides arguments for the added value of CGM-derived parameters as TIR and COV in reflecting glycaemic control in T1DM, as they relate with clinical important situations such as level 2 hyper- and hypoglycaemia. It should be noted however that the interpretation depends on HbA1c level, adding less in those with poor control as it seems not to reflect hypoglycaemia or GV.