Metrics to Evaluate Quality of Glycemic Control: Comparison of Time in Target, Hypoglycemic, and Hyperglycemic Ranges with Risk Indices

Objective: We sought to cross validate several metrics for quality of glycemic control, hypoglycemia, and hyperglycemia. Research Design and Methods: We analyzed the mathematical properties of several metrics for overall glycemic control, and for hypo- and hyperglycemia, to evaluate their similarities, differences, and interrelationships. We used linear regression to describe interrelationships and examined correlations between metrics within three conceptual groups. Results: There were consistently high correlations between %Time in range (%TIR) and previously described risk indices (M-100, Blood Glucose Risk Index [BGRI], Glycemic Risk Assessment Diabetes Equation [GRADE], Index of Glycemic Control [IGC]), and with J-Index (J). There were also high correlations among %Hypoglycemia, Low Blood Glucose Index (LBGI), percentage of GRADE attributable to hypoglycemia (GRADE(%Hypoglycemia)), and Hypoglycemia Index, but negligible correlation with J. There were high correlations of percentage of time in hyperglycemic range (%Hyperglycemia) with High Blood Glucose Index (HBGI), percentage of GRADE attributable to hyperglycemia (GRADE(%Hyperglycemia)), Hyperglycemia Index, and J. %TIR is highly negatively correlated with %Hyperglycemia but very weakly correlated with %Hypoglycemia. By adjusting the parameters used in IGC, Hypoglycemia Index, Hyperglycemia Index, or in M-R, one can more closely approximate the properties of BGRI, LBGI, or HBGI, and of GRADE, GRADE(%Hypoglycemia), or GRADE(%Hyperglycemia). Conclusions: Simple readily understandable criteria such as %TIR, %Hypoglycemia, and %Hyperglycemia are highly correlated with and appear to be as informative as risk indices. The J-Index is sensitive to hyperglycemia but insensitive to hypoglycemia.