Is interstitial fluid (ISF) a reasonable alternative for blood? What about the lag?
ISF is a reasonable alternative for blood. Glucose can be measured in the ISF–the fluid around the body’s cells where glucose freely diffuses from capillaries to the interstitial space.1 The physiological delay in ISF glucose with respect to changes in blood glucose is 2.4 ± 4.6 minutes for adults and 2.1 ± 5.0 minutes for pediatrics.2
References
1. Rebrin K, Steil GM. Can interstitial glucose assessment replace blood glucose measurements? Diabetes Technol Ther. 2000;2(3):461-472.
2. Alva S, Bailey T, Brazg R, et al. Accuracy of a 14-Day Factory-Calibrated Continuous Glucose Monitoring System With Advanced Algorithm in Pediatric and Adult Population With Diabetes. J Diabetes Sci Technol. 2022;16(1):70-77.