Glucose gradient differences in subcutaneous tissue of healthy volunteers assessed with ultraslow microdialysis and a nanolitre glucose sensor

The abdominal subcutaneous interstitium is easily accessible for monitoring glucose for Diabetes Mellitus research and management. The available glucose sensing devices demand frequent blood sampling by finger pricking for calibration. Moreover, there is controversy about the exact relationship between the levels of glucose in the subcutis and blood. In the present study ultra-slow microdialysis was applied for subcutaneous fluid sampling, allowing continuous measurement of glucose in an equilibrated fluid using a nanolitre size sensor. The present method avoids in vivo calibration. During an oral glucose tolerance test glucose levels were measured simultaneously in blood, in adipose tissue and loose connective tissue layers of the abdominal subcutis in seven healthy subjects. Fasting glucose levels (mM) were 2.52 +/- 0.77 in adipose tissue and 4.67 +/- 0.17 in blood, this difference increasing to 6.40 +/- 1.57 and 11.59 +/- 1.52 at maximal glucose concentration. Moreover, the kinetics of glucose in blood and adipose tissue were different. In contrast, connective tissue glucose levels differed insignificantly (4.71 +/- 0.21 fasting and 11.70 +/- 1.96 at maximum) from those in blood and correlated well (r2 = 0.962). Ultra-slow microdialysis combined with a nanolitre glucose sensor could be of benefit to patients in intensive diabetes therapy. Frequent blood sampling for in vivo calibration can be avoided by monitoring glucose in the abdominal subcutaneous loose connective tissue, rather than in the adipose tissue.