The added and interpretative value of CGM-derived parameters in type 1 diabetes depends on the level of glycaemic control.

OBJECTIVE: In type 1 diabetes mellitus (T1DM) management, CGM-derived parameters can provide additional insights, with the concept of time in range (TIR) and other parameters reflecting glycaemic control and variability (GV) being put forward. This study aimed to examine the added and interpretative value of the CGM-derived indices TIR and coefficient of variation (CV%) in T1DM patients stratified according to their level of glycaemic control by means of HbA1c. METHODS: T1DM patients with a minimum disease duration of 10 years and without known macrovascular disease were enrolled. Patients were equipped with a blinded CGM device (Dexcom G4) for seven days. TIR (70–180 mg/dl), time in hypoglycaemia (total: <70 mg/dl; level 2: <54 mg/dl) and hyperglycaemia (total: >180 mg/dl; level 2: >250 mg/dl) were determined, and CV% (=standard deviation(SD)/mean blood glucose(MBG)) was used as parameter for GV. Pearson and Spearman correlations, and regression analysis was used to examine associations. RESULTS: 95 patients (age: 45±10 years; HbAc1: 7.7±0.8%) were included (MBG: 159±31 mg/dl; TIR 55.8±14.9%; CV%: 43.5±7.8%) and labeled as having good (HbA1c ≤7%; n=20), moderate (7–8%; n=44) or poor (>8%; n=31) glycaemic control. HbA1c was significantly associated with MBG (rs=0.48, p<0.001) and time spent in hyperglycaemia (total: rs=0.52; level 2: r=0.46; p<0.001), but not with time in hypoglycaemia and CV%, even after analysis in HbA1c subgroups. Similarly, TIR was negatively associated with HbA1c (r=−0.53; p<0.001), MBG (rs=−0.81; p<0.001) and time in hyperglycaemia (total: rs=−0.90; level 2: rs=−0.84; p<0.001), but not with time in hypoglycaemia. Subgroup analyses, however, showed that TIR did associate with shorter time in level 2 hypoglycaemia in those patients with good (rs=−0.60; p=0.007) and moderate (rs=−0.25; p=0.047) glycaemic control. In contrast, CV% was strongly positively associated with time in hypoglycaemia (total: rs=0.78; level 2: rs=0.76; p<0.001), but not with TIR or time in hyperglycaemia in the entire cohort, although subgroup analyses showed that TIR was negatively associated with CV% in patients with good glycaemic control (r=−0.81, p<0.001) and positively in patients with poor glycaemic control (r=0.47; p<0.01). CONCLUSION: This study demonstrates that CGM-derived metrics TIR and CV% relate with clinically important situations, TIR being strongly dependent on hyperglycaemia and CV% being reflective of hypoglycaemic risk. However, the interpretation and applicability of TIR and CV%, and their relationship, depends on the level of glycaemic control of the individual patient, with CV% generally adding less clinically relevant information in those with poor control. This illustrates the need for further research and evaluation of composite measures of glycaemic control in T1DM. Abbreviations: T1DM = Type 1 diabetes mellitus; CGM = Continuous glucose monitoring; TIR = Time in range; TAR = Time above range; TBR = Time below range; GV = Glycaemic variability; CV% = Coefficient of variation; MBG = Mean blood glucose.