Diabetes Care, Vol 16, Issue 5 695-700, Copyright © 1993 by American Diabetes Association
Glucose concentration in subcutaneous extracellular space
FJ Schmidt, WJ Sluiter and AJ Schoonen
Department of Pharmaceutical Technology and Biopharmaceutics, University Centre for Pharmacy, Groningen, The Netherlands.
OBJECTIVE--To compare the subcutaneous glucose sensor measurements with two
reference methods. Previous studies provide conflicting findings about the
real glucose concentrations in subcutaneous tissue. Some suggest
substantially lower concentration, whereas others measure proportionally
higher glucose concentrations compared with the blood compartment. Before
these results can be taken seriously as an expression of the real glucose
concentration in the extracellular space, the measurements must be
validated by an independent method. RESEARCH DESIGN AND METHODS--We applied
a microdialysis-based enzyme sensor to measure glucose concentration in
subcutaneous tissue. We also developed two reference methods: subcutaneous
filtrate collection and an equilibration method 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 with the filtrate collector and taken after
a 6-h stabilization time, including the values during the glucose clamp
period, was 46 +/- 9%. The mean subcutaneous glucose concentration measured
with the glucose sensor, calibrated in vitro, was 44 +/- 8% of the mean
venous blood glucose concentration. Mean overall intercellular equilibrate
glucose concentration, i.e., the mean glucose concentration in the
subcutaneous extracellular space, taken after a 4-h stabilization time, was
46 +/- 15% of the mean venous blood glucose concentration. CONCLUSIONS--The
close agreement between the mean values of subcutaneous glucose
concentrations, obtained with three independent methods--filtration,
equilibration, and dialysis (sensor)--shows the real glucose concentration
in subcutaneous interstitial fluid is approximately 50% the blood glucose
value in normal humans. Our results clarify some of the conflicting
evidence presented in previous studies.