title: Evaluating the clinical accuracy of two continuous glucose sensors using continuous glucose-error grid analysis.
abstract: OBJECTIVE
  To compare the clinical accuracy of two different continuous glucose sensors (CGS) during euglycemia and hypoglycemia using continuous glucose-error grid analysis (CG-EGA).
  
  
  METHODS
  FreeStyle Navigator (Abbott Laboratories, Alameda, CA) and MiniMed CGMS (Medtronic, Northridge, CA) CGSs were applied to the abdomens of 16 type 1 diabetic subjects (age 42 +/- 3 years) 12 h before the initiation of the study. Each system was calibrated according to the manufacturer's recommendations. Each subject underwent a hyperinsulinemic-euglycemic clamp (blood glucose goal 110 mg/dl) for 70-210 min followed by a 1-mg.dl(-1).min(-1) controlled reduction in blood glucose toward a nadir of 40 mg/dl. Arterialized blood glucose was determined every 5 min using a Beckman Glucose Analyzer (Fullerton, CA). CGS glucose recordings were matched to the reference blood glucose with 30-s precision, and rates of glucose change were calculated for 5-min intervals. CG-EGA was used to quantify the clinical accuracy of both systems by estimating combined point and rate accuracy of each system in the euglycemic (70-180 mg/dl) and hypoglycemic (<70 mg/dl) ranges.
  
  
  RESULTS
  A total of 1,104 data pairs were recorded in the euglycemic range and 250 data pairs in the hypoglycemic range. Overall correlation between CGS and reference glucose was similar for both systems (Navigator, r = 0.84; CGMS, r = 0.79, NS). During euglycemia, both CGS systems had similar clinical accuracy (Navigator zones A + B, 88.8%; CGMS zones A + B, 89.3%, NS). However, during hypoglycemia, the Navigator was significantly more clinically accurate than the CGMS (zones A + B = 82.4 vs. 61.6%, Navigator and CGMS, respectively, P < 0.0005).
  
  
  CONCLUSIONS
  CG-EGA is a helpful tool for evaluating and comparing the clinical accuracy of CGS systems in different blood glucose ranges. CG-EGA provides accuracy details beyond other methods of evaluation, including correlational analysis and the original EGA.
authors.affiliation: Division of Pediatric Endocrinology, Department of Pediatrics, University of Virginia Health System, Box 800386, Charlottesville, VA 22908, USA. wlc@virginia.edu
authors.forename: William L
authors.initials: WL
authors.lastname: Clarke
authors.forename: Stacey
authors.initials: S
authors.lastname: Anderson
authors.forename: Leon
authors.initials: L
authors.lastname: Farhy
authors.forename: Marc
authors.initials: M
authors.lastname: Breton
authors.forename: Linda
authors.initials: L
authors.lastname: Gonder-Frederick
authors.forename: Daniel
authors.initials: D
authors.lastname: Cox
authors.forename: Boris
authors.initials: B
authors.lastname: Kovatchev
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D015190:Blood Glucose Self-Monitoring / Q000295:instrumentation* / Q000592:standards*; D003922:Diabetes Mellitus, Type 1 / Q000097:blood / Q000175:diagnosis*; D005260:Female; D015309:Glucose Clamp Technique; D006801:Humans; D007003:Hypoglycemia / Q000097:blood / Q000175:diagnosis; D008297:Male; D015203:Reproducibility of Results
chemical_list: D001786:Blood Glucose