Simple routine assay for serum urea using immobilized urease

The method described is a simple routine assay suited for a short series of serum samples. The time needed for one assay is 2 to 3 min from a stand-by arrangement. The urease is immobilized on controlled pore glass. The beads are placed in the column of an enzyme thermistor unit that is part of a continuous flow system. The heat of reaction when urea is degraded to ammonia and carbon dioxide by immobilized urease is measured and recorded continuously. The technique was investigated as regards to flow dependence, linearity, recovery, precision and some possible interfering substances. The within day precision was 0.8% (C.V.) and the day to day precision, during 56 days, was 3.0% (C.V.). Furthermore, the coefficient of correlation between results obtained with the enzyme thermistor unit and a conventional spectrophotometric method was 0.991.