Initial Evaluation of a 290-μm Diameter Subcutaneous Glucose Sensor

Results of the initial clinical evaluation in 20 human subjects of a subcutaneously implanted microsensor-based amperometrically glycemia-monitoring system, carried out between April 1994 and June 1995, are reported. The system was based on the electrical connection ("wiring") of the reaction centers of glucose oxidase to a gold electrode and on elimination of the chemicals that interfere with glucose monitoring through their horseradish peroxidase-catalyzed oxidation by internally generated hydrogen peroxide. The sensor was finer than a 29-gauge needle and had no leachable components. Because of its high selectivity for glucose, the sensor output was virtually nil at zero glucose level. This enables prompt "one-point" in vivo calibration of the sensor with a single blood glucose sample. Microsensors were subcutaneously implanted in ten nondiabetic and ten insulin-dependent diabetes mellitus (IDDM) volunteers. All subjects underwent standard meal tests and intravenous glucose-tolerance tests (IVGTT) in addition to hourly plasma glucose measurements. The sensor signals were continuously recorded, and the glucose concentration estimates were derived by calibrating the sensor using a single blood sample (one-point calibration). Regression analysis revealed that the sensor-estimated glucose concentrations were linearly related to the plasma glucose concentrations (r2 = 0.75) over a wide glucose concentration range (2-28 mmol/L) (sensor estimate = plasma 0.96 + 0.26 mmol/L). The difference between the estimated and actual glucose concentration was -0.13+/-0.23 mmol/L [mean +/-95% confidence interval (CI), n = 546], and 95% of the estimates fell in clinically acceptable zones of the Clarke error grid. The sensing delay time was 10.4+/-2.3 min as measured by the IVGTT. The subjects reported no discomfort associated with wearing the sensors.