title: Evaluating the accuracy and large inaccuracy of two continuous glucose monitoring systems.
abstract: OBJECTIVE
  This study evaluated the accuracy and large inaccuracy of the Freestyle Navigator (FSN) (Abbott Diabetes Care, Alameda, CA) and Dexcom SEVEN PLUS (DSP) (Dexcom, Inc., San Diego, CA) continuous glucose monitoring (CGM) systems during closed-loop studies.
  
  
  METHODS
  Paired CGM and plasma glucose values (7,182 data pairs) were collected, every 15-60 min, from 32 adults (36.2±9.3 years) and 20 adolescents (15.3±1.5 years) with type 1 diabetes who participated in closed-loop studies. Levels 1, 2, and 3 of large sensor error with increasing severity were defined according to absolute relative deviation greater than or equal to ±40%, ±50%, and ±60% at a reference glucose level of ≥6 mmol/L or absolute deviation greater than or equal to ±2.4 mmol/L,±3.0 mmol/L, and ±3.6 mmol/L at a reference glucose level of <6 mmol/L.
  
  
  RESULTS
  Median absolute relative deviation was 9.9% for FSN and 12.6% for DSP. Proportions of data points in Zones A and B of Clarke error grid analysis were similar (96.4% for FSN vs. 97.8% for DSP). Large sensor over-reading, which increases risk of insulin over-delivery and hypoglycemia, occurred two- to threefold more frequently with DSP than FSN (once every 2.5, 4.6, and 10.7 days of FSN use vs. 1.2, 2.0, and 3.7 days of DSP use for Level 1-3 errors, respectively). At levels 2 and 3, large sensor errors lasting 1 h or longer were absent with FSN but persisted with DSP.
  
  
  CONCLUSIONS
  FSN and DSP differ substantially in the frequency and duration of large inaccuracy despite only modest differences in conventional measures of numerical and clinical accuracy. Further evaluations are required to confirm that FSN is more suitable for integration into closed-loop delivery systems.
authors.affiliation: Metabolic Research Laboratories, Institute of Metabolic Science, Cambridge, UK.
authors.forename: Lalantha
authors.initials: L
authors.lastname: Leelarathna
authors.forename: Marianna
authors.initials: M
authors.lastname: Nodale
authors.forename: Janet M
authors.initials: JM
authors.lastname: Allen
authors.forename: Daniela
authors.initials: D
authors.lastname: Elleri
authors.forename: Kavita
authors.initials: K
authors.lastname: Kumareswaran
authors.forename: Ahmad
authors.initials: A
authors.lastname: Haidar
authors.forename: Karen
authors.initials: K
authors.lastname: Caldwell
authors.forename: Malgorzata E
authors.initials: ME
authors.lastname: Wilinska
authors.forename: Carlo L
authors.initials: CL
authors.lastname: Acerini
authors.forename: Mark L
authors.initials: ML
authors.lastname: Evans
authors.forename: Helen R
authors.initials: HR
authors.lastname: Murphy
authors.forename: David B
authors.initials: DB
authors.lastname: Dunger
authors.forename: Roman
authors.initials: R
authors.lastname: Hovorka
mesh_terms: D000293:Adolescent; D000328:Adult; D001786:Blood Glucose / Q000187:drug effects / Q000378:metabolism*; D015190:Blood Glucose Self-Monitoring / Q000295:instrumentation* / Q000379:methods; D003922:Diabetes Mellitus, Type 1 / Q000097:blood* / Q000188:drug therapy; D016503:Drug Delivery Systems / Q000295:instrumentation*; D004739:England; D004867:Equipment Design; D005260:Female; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage*; D007328:Insulin / Q000008:administration & dosage*; D007332:Insulin Infusion Systems; D008297:Male; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012648:Self Care
chemical_list: D001786:Blood Glucose; D007004:Hypoglycemic Agents; D007328:Insulin