title: Continuous glucose monitoring in subcutaneous tissue using factory-calibrated sensors: a pilot study.
abstract: BACKGROUND
  Commercial continuous subcutaneous glucose monitors require in vivo calibration using capillary blood glucose tests. Feasibility of factory calibration, i.e., sensor batch characterization in vitro with no further need for in vivo calibration, requires a predictable and stable in vivo sensor sensitivity and limited inter- and intra-subject variation of the ratio of interstitial to blood glucose concentration.
  
  
  METHODS
  Twelve volunteers wore two FreeStyle Navigator (Abbott Diabetes Care, Alameda, CA) continuous glucose monitoring systems for 5 days in parallel for two consecutive sensor wears (four sensors per subject, 48 sensors total). Sensors from a prototype sensor lot with a low variability in glucose sensitivity were used for the study. Median sensor sensitivity values based on capillary blood glucose were calculated per sensor and compared for inter- and intra-subject variation. Mean absolute relative difference (MARD) calculation and error grid analysis were performed using a single calibration factor for all sensors to simulate factory calibration and compared to standard fingerstick calibration.
  
  
  RESULTS
  Sensor sensitivity variation in vitro was 4.6%, which increased to 8.3% in vivo (P < 0.0001). Analysis of variance revealed no significant inter-subject differences in sensor sensitivity (P = 0.134). Applying a single universal calibration factor retrospectively to all sensors resulted in a MARD of 10.4% and 88.1% of values in Clarke Error Grid Zone A, compared to a MARD of 10.9% and 86% of values in Error Grid Zone A for fingerstick calibration.
  
  
  CONCLUSIONS
  Factory calibration of sensors for continuous subcutaneous glucose monitoring is feasible with similar accuracy to standard fingerstick calibration. Additional data are required to confirm this result in subjects with diabetes.
authors.affiliation: Abbott Diabetes Care, Alameda, CA 94502, USA. udo.hoss@abbott.com
authors.forename: Udo
authors.initials: U
authors.lastname: Hoss
authors.forename: Iman
authors.initials: I
authors.lastname: Jeddi
authors.forename: Mark
authors.initials: M
authors.lastname: Schulz
authors.forename: Erwin
authors.initials: E
authors.lastname: Budiman
authors.forename: Claire
authors.initials: C
authors.lastname: Bhogal
authors.forename: Geoffrey
authors.initials: G
authors.lastname: McGarraugh
mesh_terms: D000293:Adolescent; D000328:Adult; D001786:Blood Glucose / Q000032:analysis*; D015190:Blood Glucose Self-Monitoring / Q000295:instrumentation* / Q000379:methods; D002138:Calibration; D003922:Diabetes Mellitus, Type 1 / Q000097:blood*; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory / Q000295:instrumentation* / Q000379:methods; D010865:Pilot Projects
chemical_list: D001786:Blood Glucose