A Novel Composite Glucose Index (COGI) for Evaluating Closed-Loop Performance in Type 1 Diabetes
Authors: LEELARATHNA LALANTHA , THABIT HOOD , BALLY LIA , WILINSKA MALGORZATA E. , MADER JULIA K. , PIEBER THOMAS R. , EVANS MARK , HOVORKA ROMAN 
Published: June 2018

Presently, no single index exists that summarizes key aspects of continuous glucose monitoring (CGM) data. Such an index may be useful in evaluating outcomes in closed-loop (CL) as well as other novel diabetes technology studies utilizing CGM. Here we present a novel composite glucose index (COGI), encompassing three key elements of CGM (Table). The total index ranges from 0 to 100, where 100 approximates glucose profile of people without diabetes. One percent reduction of time &lt;70mg/dl is equivalent to 4.7% increase in time in range (TIR) and 9mg/dl reduction in standard deviation of CGM is equivalent to 3% increase in TIR. We used the COGI to assess the incremental benefits of day-and-night hybrid CL on glucose control compared to insulin pump therapy during a previously reported randomized cross-over, 4-week study in adults with well-controlled type 1 diabetes (n=28, mean, baseline HbA1c 6.9% (52 mmol/mol), age 41 years, duration of diabetes 24 years). Mean (SD) of COGI was 60(11) (range 41 to 80) during the control period, which improved to 75 (7) (range 58 to 86) during CL (paired difference: +15, p&lt;0.0001, 95% CI +11 to +18). We demonstrate a novel composite glucose index based on CGM which improved considerably during CL, even in those with optimal HbA1c. A composite CGM-based metric may thus have a role in evaluating glycemic control attributable to CL and other novel technologies beyond HbA1c.Composition of the COGI and relative contributions of its three componentsGlucose AreaCGM metricRange and scoring of the metricRelative Contribution to COGI(%)Time in range (TIR)Percent time spent between 70 to 180mg/dlTIR from 0% to 100% where 0% TIR is given 0 points and 100% TIR is given 100 points50Time in hypoglycemia (TIH)Percent time spent below 70mg/dlTIH from 0% to 15% where 0% TIH is given 100 points and TIH 15% and above is given 0 points35Glucose variability (GV)Standard deviation (SD)SD from 18 to 108mg/dl where SD 18mg/dl and below is given 100 points and SD 108mg/dl and above is given 0 points15

Disclosure
L. Leelarathna: Advisory Panel; Self; Novo Nordisk A/S. Speaker's Bureau; Self; Novo Nordisk A/S. Advisory Panel; Self; Sanofi. Speaker's Bureau; Self; Insulet Corporation, Medtronic MiniMed, Inc.. Advisory Panel; Self; Roche Diabetes Care Health and Digital Solutions, Abbott. H. Thabit: None. L. Bally: None. M.E. Wilinska: None. J.K. Mader: Speaker's Bureau; Self; Roche Diabetes Care Health and Digital Solutions, Novo Nordisk A/S. Advisory Panel; Self; Eli Lilly and Company. Consultant; Self; Becton, Dickinson and Company. Speaker's Bureau; Self; Sanofi. Research Support; Self; ConvaTec Inc., Menarini Group. Speaker's Bureau; Self; Medtronic. Research Support; Self; Novo Nordisk A/S, Sanofi. T.R. Pieber: Consultant; Self; Arecor, AstraZeneca, Eli Lilly and Company, Novo Nordisk A/S, Sanofi. Employee; Self; CBmed. Research Support; Self; Novo Nordisk A/S, AstraZeneca. M. Evans: Advisory Panel; Self; Novo Nordisk A/S, Eli Lilly and Company, Cellnovo, Roche Pharma. Speaker's Bureau; Self; Abbott, Novo Nordisk A/S. R. Hovorka: Speaker's Bureau; Self; Novo Nordisk A/S. Advisory Panel; Self; Novo Nordisk A/S. Speaker's Bureau; Self; Eli Lilly and Company, AstraZeneca. Other Relationship; Self; B. Braun Medical Inc.. Research Support; Self; Medtronic. Other Relationship; Self; Medtronic. Research Support; Self; Abbott, JDRF, Diabetes UK, National Institute of Diabetes and Digestive and Kidney Diseases.