Calibration problems of subcutaneous glucosensors when applied "in-situ" in man

Continuous glucose monitoring is the conditio sine qua non to achieve total automation in glucose-controlled insulin-delivery. Several types of glucosensors have been designed according to the enzyme-amperometric method to measure the glucose in different human compartments. However, problems such as long-term stability and calibration prevent this technique being put into practice. A feasible method is needed to calibrate the glucosensor and at the same time should be accepted by the patients. To achieve calibration we determined the absolute tissue glucose, as well as the microdialysis recovery in-vivo, in healthy subjects under normal conditions and during a hyperglycaemic clamp by applying a device based on the recirculation of phosphate buffer saline in a microdialysis probe implanted in the s.c. adipose tissue. The first experiments carried out were promising and encouraging, but further investigations are still needed to favour an ideal "before implantation, all in-vitro" method to calibrate a s.c. glucosensor.