A Comparison of the Original vs. Modified Continuous Glucose Monitoring System (CGMS™) Sensor During Hypoglycemia in the Diabetes Research in Children Network (DirecNet) Accuracy Study.
A Comparison of the Original vs. Modified Continuous Glucose Monitoring System (CGMS™) Sensor During Hypoglycemia in the Diabetes Research in Children Network (DirecNet) Accuracy Study
Michael Tansey1, Roy Beck2, Bruce Buckingham3, Nelly Mauras4, Rosanna Fiallo-Scharer5, Dongyuan Xing2, William Tamborlane6, Katrina Ruedy2, and the Diabetes Research in Children Network (DirecNet) Study Group.
1Department of Pediatrics, University of Iowa, Carver College of Medicine, Iowa City, IA; 2Jaeb Center for Health Research, Tampa, FL; 3Division of Pediatric Endocrinology and Diabetes, Stanford University, Stanford, CA; 4Nemours Children’s Clinic, Jacksonville, FL; 5Barbara Davis Center for Childhood Diabetes, University of Colorado, Denver, CO; 6Department of Pediatrics, Yale University School of Medicine, New Haven, CT.
The CGMS has been used to follow glucose trends in patients with type1 diabetes, however the accuracy of this device to document hypoglycemia has not been completely evaluated. Recently, the manufacturer of CGMS(Medtronic MiniMed, Northridge, CA) developed a modified glucose sensor using a new fabrication process. To study the accuracy of these sensors, the DirecNet study group examined 91 patients, 3-17 years of age with type 1 diabetes. CGMS glucose values were compared with simultaneous reference venous glucose values, sampled every 30-60 minutes for 24 hours and every 5 minutes for up to 90 minutes during an insulin-induced hypoglycemia test. When all sensor values were analyzed, the 25 CGMSs using modified sensors were substantially more accurate than the 115 CGMSs using original sensors in median error (11% versus 19%, P<0.001) and percentage meeting ISO criteria (72% versus 53%, P<0.001). During hypoglycemia, both original and modified sensors were less accurate than during hyperglycemia, and the enhanced accuracy with the modified sensors was less apparent for hypoglycemia than hyperglycemia. As indicated in the Table below, the original sensors accurately identified only 36% of Reference Glucose (RG) values < 60 mg/dL vs 49% with the modified sensors. All of the modified sensor values were <100 mg/dL when the RG was <60 mg/dL whereas 15% of the original sensor values were >100 mg/dL. Only 8 of 26 overnight hypoglycemic episodes detected by original sensors were RG confirmed, whereas all 3 detected by modified sensors were RG confirmed.Conclusion: Recent modifications to the CGMS sensor have resulted in substantially better accuracy. However, even the modified sensors differ substantially from RG glucose values in the hypoglycemic range.
Data pooled from three studies:
* Absolute value of sensor glucose minus reference glucose.
(Pilot / RCT)
H. Peter Chase
University of Iowa
Nemours Children’s Clinic