GLUCOSE-CONCENTRATION IN SUBCUTANEOUS EXTRACELLULAR-SPACE

OBJECTIVE- To compare the subcutaneous glucose sensor measurements wit h two reference methods. Previous studies provide conflicting findings about the real glucose concentrations in subcutaneous tissue. Some su ggest substantially lower concentration, whereas others measure propor tionally higher glucose concentrations compared with the blood compart ment. Before these results can be taken seriously as an expression of die real glucose concentration in the extracellular space, the measure ments must be validated by an independent method. RESEARCH DESIGN AND METHODS- We applied a microdialysis-based enzyme sensor to measure glu cose concentration in subcutaneous tissue. We also developed two refer ence methods: subcutaneous filtrate collection and an equilibration me thod using ultrafiltration membranes to support the earlier findings. We provided an anatomical model to explain the results. RESULTS - The mean overall intercellular filtrate glucose concentration, sampled wit h the filtrate collector and taken after a 6-h stabilization time, inc luding die values during the glucose clamp period, was 46 +/- 9%. The mean subcutaneous glucose concentration measured with the glucose sens or, calibrated in vitro, was 44 +/- 8% of the mean venous blood glucos e concentration. Mean overall intercellular equilibrate glucose concen tration, i.e., the mean glucose concentration in the subcutaneous extr acellular space, taken after a 4-h stabilization time, was 46 +/- 15% of the mean venous blood glucose concentration. CONCLUSIONS - The clos e agreement between the mean values of subcutaneous glucose concentrat ions, obtained with three independent methods-filtration, equilibratio n, and dialysis (sensor)-shows die real glucose concentration in subcu taneous interstitial fluid is approximately 50% the blood glucose valu e in normal humans. Our results clarify some of the conflicting eviden ce presented in previous studies.