Can interstitial glucose assessment replace blood glucose measurements?

Current treatment regiments for individuals depending on exogenous insulin are based on measurements of blood glucose obtained through painful finger sticks. The shift to minimal or noninvasive continuous glucose monitoring primarily involves a shift from blood glucose measurements to devices measuring subcutaneous interstitial fluid (ISF) glucose. As the development of these devices progresses, details of the dynamic relationship between blood glucose and interstitial glucose dynamics need to be firmly established. This is a challenging task insofar as direct measures of ISF glucose are not readily available. The current article investigated the dynamic relationship between plasma and ISF glucose using a model-based approach. A two-compartment model system previously validated on data obtained with the MiniMed Continuous Glucose Monitoring System (CGMS) is reviewed and predictions from the original two-compartment model were confirmed using new data analysis of glucose dynamics in plasma and hindlimb lymph (lymph is derived from ISF) in the anesthetized dog. From these data sets, the time delay between plasma and ISF glucose in dogs was established (5-12 minutes) and a simulation study was performed to estimate the errors introduced if ISF is taken as a surrogate for blood. From the simulation study, the error component resulting from the differences in plasma and ISF glucose was estimated to be < 6% during normal day-to-day use in an individual with diabetes (error component calculated as the standard deviation of the ISF/plasma glucose differences under conditions where the maximal time delay was used). This difference is most likely within the variance between arterial and venous blood glucose. We conclude that the differences between plasma and ISF glucose will not be a significant obstacle in advancing the use of ISF as an alternative to blood glucose measurements.