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DirecNet Study of the Accuracy of the Navigator Continuous Glucose

This study evaluates the accuracy of the FreeStyle Navigator™ Continuous Glucose Monitoring System in children and adolescents with type 1 diabetes mellitus in inpatient and outpatient settings. The study group, DirecNet, aims to assess the clinical usefulness of glucose sensor devices in youth with T1DM. The Navigator system measures interstitial glucose, requires calibration at specific intervals, and provides glucose readings every 60 seconds. Inpatient procedures involved clinical center admission, venous blood sampling, and monitored exercise. Outpatient participants wore the Navigator daily and used a FreeStyle meter for reference values. The study measured accuracy using traditional and near-continuous glucose monitoring methods. Results indicated comparable accuracy in both inpatient and outpatient settings, with glucose concentration having minimal impact on system performance.

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DirecNet Study of the Accuracy of the Navigator Continuous Glucose

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  1. DirecNet Study of the Accuracy of the Navigator Continuous Glucose Monitoring System in Children and Adolescents with Type 1 Diabetes Darrell Wilson1, Katrina Ruedy2, Craig Kollman2, Roy Beck2, William Tamborlane3, Larry Fox4, Stuart Weinzimer3, Barb Tallant5 and the Diabetes Research in Children Network (DirecNet) Study Group 1Stanford, CA; 2Tampa, FL; 3 New Haven, CT; 4Jacksonville, FL; 5 Denver, CO.

  2. Background • The Diabetes Research in Children Network (DirecNet) is an NIH-funded collaborative study group. • The major objective of DirecNet is to critically evaluate the clinical usefulness of current and future glucose sensor devices in youth with T1DM.

  3. Goals • One of the goals of this study was to determine the accuracy of the FreeStyle Navigator™ Continuous Glucose Monitoring System, an investigational device, (Abbott Diabetes Care, Alameda, CA) in children with Type 1 diabetes mellitus (T1DM) in both the inpatient (CRC) and outpatient environment.

  4. FreeStyle Navigator™ Continuous Glucose Monitoring System • Measures interstitial glucose • Requires calibration at 10, 12, 24 and 72 hours after sensor insertion • Provides glucose readings every 60 seconds for up to 120 hours • Values range from 20 to 500 mg/dL • Also displays trend arrow for glucose rate of change

  5. Subject Selection • Type 1 diabetes for at least 1 year • Age 3 to <18 years • Using a downloadable insulin infusion pump for a least 6 months • Home computer with email access

  6. Study ProceduresInpatient • Admitted to Clinical Research Center • Approximately 24 hours • Two Navigators: one inserted at home prior to admission and second placed at time of admission • Venous blood sampling • Every 30 minutes • Every 10 minutes for 1 hour after breakfast • Insulin bolus delayed until after 1 hour of blood draws complete (correction dose given at start if BG >250) • Central lab for reference glucoses • Exercise session for those older than 7 yrs • Four 15-min sessions walking on a treadmill at a target heart rate 140 bpm interspersed with three 5-min rest breaks

  7. Study ProceduresOutpatient • Subjects instructed to wear Navigator on a daily basis • FreeStyle meter used for outpatient reference glucoses • Meter values used to calibrate the Navigator were excluded for the accuracy evaluation

  8. Navigator FunctionOutpatient • Sensor successfully calibrated 96% • Hours per Sensor WornData • < 24 hours 6% 18% • 24 - <48 hours 13% 11% • 48 - <72 hours 13% 13% • 72 - < 96 hours 15% 15% • ≥ 96 hours53% 42% • mean ± SD (hours) 89 ± 35 71 ± 38

  9. Evaluation of AccuracyPoint to Point Analysis The appropriate set of accuracy measures to evaluate near continuous glucose monitoring remains to be developed. We used the traditional methods that are utilized to assess the accuracy of blood glucose meters. These methods do not capture the time dimension of glucose sensor data with respect to glucose trend (slope) information or glucose pattern detection across the day.

  10. Measures of AccuracyPoint to Point • Difference • sensor – reference • Absolute difference • |sensor – reference| • Relative absolute difference (RAD) % • |(sensor – reference)/reference| x 100% • ISO criteria • Reference glucose ≤75 mg/dL • Sensor value within ±15 mg/dL • Reference glucose value >75 mg/dL • Sensor value within ±20%

  11. Subject Characteristics30 Subjects

  12. Sample Inpatient Navigator Data

  13. Navigator Inpatient Point Accuracy (excludes exercise and post-breakfast challenge) • Number of pairs: 1,811 • Median difference, -2 mg/dL, • Not significantly different than zero • Hypoglycemia (reference ≤70 mg/dL) • Median absolute difference = 14 mg/dL (25th-75th %-iles: 8, 22 mg/dL) • Target Range(reference 71-180 mg/dL) • Median RAD = 13% (25th-75th %-iles: 6%, 22%) • Hyperglycemia (reference >180 mg/dL) • Median RAD = 10% (25th-75th %-iles: 5%, 18%)

  14. Navigator Outpatient Point Accuracy • Number of pairs: 8,639 • Median difference = -1 mg/dL, • Hypoglycemia (reference ≤70 mg/dL) • Median absolute difference = 15 mg/dL (25th-75th %-iles: 7, 26 mg/dL) • Target Range(reference 71-180 mg/dL) • Median RAD = 15% (25th-75th %-iles: 7%, 27%) • Hyperglycemia (reference >180 mg/dL) • Median RAD = 12% (25th-75th %-iles: 6%, 21%)

  15. Accuracy(Outpatient)* did not Deteriorate with Age of Sensor * Inpatient results were similar (data not shown)

  16. Effect of Glucose Concentration

  17. Lead/Lag AnalysisInpatient Data (excludes exercise and post-breakfast challenge) Median Median % DifferenceRADISO 30 min lead +1 18% 55% 20 min lead 0 16% 61% 10 min lead -1 14% 67% No lag/lead -2 12% 74% 10 min lag -3 11% 78% 20 min lag -4 11% 77% 30 min lag -4 13% 71%

  18. Event AnalysisGlycemic Excursions during Exercise N=20 subjects participated in exercise test median (25th-75th percentiles) NavigatorLabDifferenceAbs. Diff. Baseline 170 177 -10 (-24, +21) 23 (15, 29) Glucose Dropa 8589 -5 (-21, +6) 11 (5, 22) Minutes to Nadir 85 77 +3 (-7, +14) 8 (4, 14) Rate of Changeb 1.0 1.2 -0.1 (-0.3, +0.1) 0.1 (0.1, 0.3) a-baseline minus nadir; b-mg/dL/minute (timed from baseline to nadir)

  19. Event AnalysisGlycemic Excursions during Exercise Fall in Glucose from Baseline to Nadir (mg/dL)

  20. False positive rate: % Navigator events for which the reference is >70 mg/dL and >10 mg/dL higher than the concurrent Navigator value*: 13/35 = 37% (inpatient) 179/642 = 28% (outpatient) Sensitivity rate: % Reference events for which there is a Navigator value <70 mg/dL within ±30 min of the first low reference*: 23/47 = 49% (inpatient) 568/911 = 62% (outpatient) Event AnalysisDetection of Hypoglycemia(Glucose values <70 mg/dL within ± 30 min treated as a single event) * If all Navigator values within 10 mg/dL of a concurrent reference, but on the other side of the 70 mg/dL threshold (e.g., Navigator=68/reference=72), then the event is not counted as a failure or a success (excluded from calculation).

  21. Side Effects • There were 2 cases of severe skin reactions thought to be allergic reactions to the sensor adhesive • No other problems

  22. Summary & Conclusions In summary, accuracy of the Navigator in the home environment is similar to accuracy in an inpatient setting. The sensor continues to perform well even during the 5th day of wear and functions as well during the night as during the day. The sensor glucose values are generally within 5-20% of the serum glucose. This level of accuracy is sufficient for detecting trends and modifying diabetes management.

  23. Acknowledgements • This study would not have been possible without the support of CRC Nurses at the study sites. • This research has been supported by the following NIH/NICHD Grants: HD041919; HD041915; HD041890; HD041918; HD041908; and HD041906. • Clinical Centers also received funding through the following GCRC Grant Numbers M01 RR00069; RR00059; M01 RR 06022 and 5M01RR00070 and Nemours Biomedical Research. • DirecNet Central Laboratory: University of Minnesota Central Laboratory • Michael Steffes, Jean Bucksa, Maren Nowicki

  24. Barbara Davis Center • H. Peter Chase • Rosanna Fiallo-Scharer • Laurel Messer • Barbara Tallant • University of Iowa • Eva Tsalikian • Michael Tansey • Linda Larson • Julie Coffey • Joanne Cabbage • Nemours Children’s Clinic • Tim Wysocki • Nelly Mauras • Larry Fox • Keisha Bird • Kim Englert • Stanford University • Bruce Buckingham • Darrell Wilson • Jennifer Block • Paula Clinton • Yale University • William Tamborlane • Stuart Weinzimer • Elizabeth Doyle • Melody Martin • Amy Steffen • Jaeb Center for Health Research • Roy Beck • Katrina Ruedy • Craig Kollman • Dongyuan Xing • Cynthia Stockdale

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