Development of the model for the optical monitoring of urea in spent dialysate

The aim of the study was to develop a mathematical model suitable for the estimation of urea concentration removed during dialysis through UV-absorbance. 29 haemodialysis patients on chronic three-times-a-week haemodialysis were studied in 6 separate studies. Double-beam spectrophotometer was used for the determination of UV-absorbance in the collected spent dialysate samples. A single wavelength (SW) and a multi-wavelength (MW) model were developed using stepwise regression utilizing urea values from the laboratory as the dependent parameter. For SW model R² was 0.656 (calibration set) and 0.729 (validation set), for MW model R² was 0.696 and 0.764, respectively. In summary, the urea concentration removed during dialysis can be estimated with UV-absorbance technique.