Robust, reliable biosensor for continuous monitoring of urea during dialysis.

We developed a new urea sensor for the on-line monitoring of hemodialysis adequacy. The biosensor consisted of an immobilized urease cartridge placed between magnetoinductive conductivity cells. The biosensor output was taken as the conductivity difference between these cells. The device was placed on the ultrafiltrate line of a paired filtration dialysis system. The amount of urease present in the cartridge was sufficient for the complete conversion to ammonium carbonate of urea up to 35 mmol/L. Agreement was good between the urea concentration by the biosensor method and an automated analyzer for seven patients: range 8.07-30.3 mmol/L (22.6-84.8 mg/dL blood urea nitrogen, BUN); intercept 0.20 +/- 0.1 mmol/L (0.55 +/- 0.4 mg/dL BUN); slope 1.01 +/- 0.01; r 0.997; S(y/x) 0.40 mmol/L (1.11 mg/dL BUN). The device proposed meets the requirements of accuracy, cost, ruggedness, and ease of use (no calibration required) for a biosensor to be used for continuous monitoring of hemodialysis.