DEVELOPMENT OF A BIPARAMETRIC BIOANALYSER FOR CREATININE AND UREA - VALIDATION OF THE DETERMINATION OF BIOCHEMICAL PARAMETERS ASSOCIATED WITH HEMODIALYSIS

The construction and evaluation of an automated urea and creatinine bi parametric biosystem using flow injection analysis (FIA) are described . The biosystem uses enzyme reactions that hydrolyse urea and creatini ne producing ammonium ions. The enzymes used were creatinine deiminase and urease, which are immobilized covalently in flow reactors, The re actor with creatinine deiminase has the enzyme immobilized on controll ed-pore glass beads, whereas urease is immobilized on a nylon open tub ular reactor. Detection is realised with a flow-through ammonium ion-s elective electrode with an inner solid-state contact (graphite-epoxy c omposite). Ammonium ions are separated from alkali ion interferents th rough a gas-diffusion cell. The bioanalyser is fully automated using s oftware and electronics developed ex profeso in our laboratories. The analyser was validated off-line by measuring urea and creatinine from discrete effluent samples from hemodialysis equipment. Results agreed with concurrent analyses realised using hospital laboratory methods. T here were no significant differences between the two sets of results a t the 95% confidence level, Finally, the biparametric bioanalyser was validated on-line by measuring creatinine and urea levels in artificia l kidney effluents, These measurements were useful in the determinatio n of key biochemical parameters of clinical interest such as the mass of urea and creatinine extracted from the patient as well as the initi al concentration of creatinine and urea in blood plasma. When the resu lts of the bioanalyser mere compared with those yielded by the usual m ethods, they showed no significant differences at the 95% confidence l evel when determining the mass of the analytes extracted by the hemodi alyser or when determining the urea concentration in blood plasma. How ever, when measuring the creatinine concentration in blood plasma usin g the developed bioanalyser, significant differences appeared.