Looking Beyond HbA1c—Evaluating Glycaemic Control during Closed-Loop Use in Type 1 Diabetes
Authors: THABIT HOOD , LEELARATHNA LALANTHA , WILINSKA MALGORZATA E. , BENESCH CARSTEN , ARNOLDS SABINE , MADER JULIA K. , PIEBER THOMAS R. , EVANS MARK , HOVORKA ROMAN 
Published: June 2018

Despite being an established marker of glucose control, HbA1c does not provide insight into hypoglycemia and glycemic variability. As such, HbA1c does not capture these vital attributes of particular interest during closed-loop insulin delivery (CL). We developed a novel index using continuous glucose monitoring (CGM) data, named composite glucose index (COGI), which evaluates CL performance based on 3 key aspects: time in range 70-180mg/dl, hypoglycemia &lt;70mg/dl and glucose variability, each contributing up to 50, 35 and 15 points to the composite index respectively. COGI ranges from 0 (worst control) to 100 (best control). We used COGI to assess glucose control in a published, randomised, 3 months day-and-night hybrid CL study in type 1 diabetes adults (n=32, baseline A1c 7.6% (60 mmol/mol), diabetes duration 21 years), compared to sensor augmented pump therapy. We hypothesized that COGI may show benefits of CL even in the absence/limited HbA1c improvement. For the whole cohort, HbA1c difference was -0.3±0.6% (P=0.002) in favour of CL, and COGI improved by +10 (p&lt;0.005, 95% CI 7 to 11). In those without HbA1c improvement (n=15) notably, overall COGI and individual components improved with CL use (Table), mainly attributable to the hypoglycemia component of COGI. We demonstrate the wider benefits of CL using a novel composite CGM index. COGI may have a role in evaluating glycemic control during CL use, beyond HbA1c.HbA1c and composite glucose index (COGI) in those without HbA1c improvementClosed-loop Sensor augmented pump therapy P ValueHbA1c (%) end of treatment arm7.0±0.96.8±1.00.056 COGI (out of 100 points)71±660±10&lt;0.001 Time in range component (out of 50 points)36±533±60.003Hypoglycemia component (out of 35 points)26±419±90.001 Glycemic variability component (out of 15 points)9±28±20.029

Disclosure
H. Thabit: None. 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. M.E. Wilinska: None. C. Benesch: None. S. Arnolds: 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.