Effects of microdialysis catheter insertion into the subcutaneous adipose tissue assessed by the SCGM1 system

To monitor glucose in patients with diabetes continuously a microdialysis-based glucose sensor system (SCGM1 System, Roche Diagnostics GmbH, Mannheim, Germany) is under clinical development. This system allows monitoring of glucose levels in the subcutaneous interstitial fluid of patients with diabetes for a maximum duration of up to 120 h. The aim of the study was to determine the effect of microdialysis catheter insertion on the stability of the SCGM1 System glucose sensor signal. At four study sites, 47 experiments with the prototype of the novel SCGM1 System were performed in 42 patients with type 1 diabetes; two additional experiments were performed in two healthy volunteers. The microdialysis catheter was inserted in the subcutaneous adipose tissue of the patients in order to measure the glucose concentration in the interstitial fluid continuously. The catheter was perfused with a pump rate of 0.3 microL/min. For method comparison capillary blood glucose measurements were performed as reference values. In addition, the skinfold thickness was measured. Out of the total of 49 experiments 34 were usable. The average monitoring time in these experiments was 106.0 +/- 14.3 h (mean +/- SD). However, for this study the data from the first study day were evaluated in more detail. The analysis showed that during the first 12 h after catheter insertion the sensor signal increased 20% in comparison with the capillary blood glucose values (normalized calibration factor). This leads to a lower normalized calibration factor compared with the following study days. It remains stable in the time thereafter. The skinfold thickness showed no significant effect on the sensor signal. The observed increase in sensor signal in the first hours after insertion of the microdialysis catheter was probably due to a local trauma, which can induce an inflammation reaction. Thereafter, the signal registered by the SCGM1 System was stable and free of drift to the end of the experiment.