Timing of Changes in Interstitial and Venous Blood Glucose Measured With a Continuous Subcutaneous Glucose Sensor

Timing of Changes in Interstitial and Venous Blood Glucose Measured With a Continuous Subcutaneous Glucose Sensor Michael S. Boyne , David M. Silver , Joy Kaplan and Christopher D. Saudek From the Division of Endocrinology and Metabolism, Johns Hopkins University School of Medicine and the Applied Physics Laboratory, Johns Hopkins University, Baltimore, Maryland Address correspondence and reprint requests to Christopher D. Saudek, MD, Johns Hopkins University School of Medicine, Osler 576, 600 North Wolfe St., Baltimore, MD 21287. E-mail: csaudek{at}jhu.edu Abstract The objective of this study was to use a subcutaneous continuous glucose sensor to determine time differences in the dynamics of blood glucose and interstitial glucose. A total of 14 patients with type 1 diabetes each had two sensors (Medtronic/MiniMed CGMS) placed subcutaneously in the abdomen, acquiring data every 5 min. Blood glucose was sampled every 5 min for 8 h, and two liquid meals were given. A smoothing algorithm was applied to the blood glucose and interstitial glucose curves. The first derivatives of the glucose traces defined and quantified the timing of rises, peaks, falls, and nadirs. Altogether, 24 datasets were used for the analysis of time differences between interstitial and blood glucose and between sensors in each patient. Time differences between blood and interstitial glucose ranged from 4 to 10 min, with the interstitial glucose lagging behind blood glucose in 81% of cases (95% CIs 72.5 and 89.5%). The mean (±SD) difference between the two sensors in each patient was 6.7 ± 5.1 min, representing random variation in sensor response. In conclusion, there is a time lag of interstitial glucose behind blood glucose, regardless of whether glycemia is rising or falling, but intersensor variability is considerable in this sensor system. Comparisons of interstitial and blood glucose kinetics must take statistical account of variability between sensors. CGMS, continuous glucose monitoring system FDA, Food and Drug Administration IV, intravenous Footnotes Accepted August 18, 2003. Received December 2, 2002. DIABETES