title: Do sensor glucose levels accurately predict plasma glucose concentrations during hypoglycemia and hyperinsulinemia?
abstract: OBJECTIVE
  The MiniMed Continuous Glucose Monitoring System (CGMS) measures subcutaneous interstitial glucose levels that are calibrated against three or more fingerstick glucose levels daily. The objective of the present study was to examine whether the relationship between plasma and interstitial fluid glucose is altered by changes in plasma glucose and insulin levels and how such alterations might influence CGMS performance.
  
  
  METHODS
  Arterialized plasma glucose, sensor glucose, and interstitial fluid glucose were measured by microdialysis in 11 healthy subjects during a 1.0 mU. kg(-1). min(-1) stepped euglycemic-hypoglycemic-hyperglycemic (plasma glucose approximately 5, 3.1, and 8.6 mmol/l, respectively) insulin clamp that raised plasma insulin to approximately 360-390 pmol/l.
  
  
  RESULTS
  When the CGMS was calibrated versus plasma glucose levels before insulin infusion, basal sensor and plasma glucose were similar (5.0 +/- 0.3 vs. 5.2 +/- 0.3 mmol/l, respectively); dialysate glucose was 3.3 +/- 0.9 mmol/l. During the hyperinsulinemic-euglycemia study (plasma glucose 4.9 +/- 0.3 mmol/l), dialysate glucose fell by 30-35%, accompanied by a significant reduction in sensor glucose (to 3.7 +/- 0.6 mmol/l; P < 0.001 vs. plasma). Subsequently, sensor levels remained lower than plasma values during mild hypoglycemia (2.5 +/- 0.6 vs. 3.1 +/- 0.3 mmol/l; P < 0.01) and during recovery from hypoglycemia (7.3 +/- 1.2 vs. 8.6 +/- 0.6; P < 0.01). However, when the CGMS was calibrated against plasma glucose levels before and during each step of the clamp, sensor glucose levels increased throughout the study and did not differ from plasma glucose values during hypoglycemia.
  
  
  CONCLUSIONS
  Although hyperinsulinemia may contribute to modest discrepancies between plasma and sensor glucose levels, the CGMS is able to accurately track acute changes in plasma glucose when calibrated across a range of plasma glucose and insulin levels.
authors.affiliation: Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut 06520, USA. teresa.monsod@yale.edu
authors.forename: Teresa P
authors.initials: TP
authors.lastname: Monsod
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Flanagan
authors.forename: Fran
authors.initials: F
authors.lastname: Rife
authors.forename: Rebecca
authors.initials: R
authors.lastname: Saenz
authors.forename: Sonia
authors.initials: S
authors.lastname: Caprio
authors.forename: Robert S
authors.initials: RS
authors.lastname: Sherwin
authors.forename: William V
authors.initials: WV
authors.lastname: Tamborlane
mesh_terms: D000293:Adolescent; D000328:Adult; D001786:Blood Glucose / Q000032:analysis*; D002138:Calibration; D005260:Female; D015309:Glucose Clamp Technique; D006801:Humans; D006946:Hyperinsulinism / Q000097:blood*; D007003:Hypoglycemia / Q000097:blood*; D007328:Insulin / Q000097:blood*; D008297:Male; D017551:Microdialysis / Q000295:instrumentation / Q000379:methods*; D018670:Monitoring, Ambulatory / Q000295:instrumentation* / Q000592:standards
chemical_list: D001786:Blood Glucose; D007328:Insulin