Urea and Lactate Determined in 1-pt Whole-Blood Samples with a Miniaturized Thermal Biosensor

A miniaturizedflow-injected thermal biosensor was developed for the determination of urea and L-lactate in undilutedblood in 1-L samples. The sensor employed a smallenzyme column constructedof stainlesssteeltubing and microbead thermistors. Urease and lactate oxidase/catalase were separately immobilized onto controlled-pore glass beads, which, in turn, were charged into the enzyme column. With a flow rate of 70 .tL/min, linear analytical ranges from 0.2 to at least 50 mmol/L and 0.2 to 14 mmol/L were obtained for urea and lactate, respectively. The relative standard deviations (CVs) for measurements of analyte in buffer were 0.91% for urea and 1.84% for lactate. For urea in whole blood, the CV for 50 determinations was 4.1%. Contrived samples containing various concentrations of urea and L-lactate in whole blood were determined with this sensor and with a spectrophotometric method. Comparisons of the results gave correlation coefficients of 0.989 and 0.984 for 30 blood urea and 30 blood lactate assays inconcentrationsranging from 4 to 20.9 mmol/L and from 1.7 to 12.7 mmol/L respectively.