Evaluation of Urea Reduction Ratio Estimated From the Integrated Value of Urea Concentrations in Spent Dialysate

We propose a new apparatus and method to estimate accurate urea reduction ratio without influence of any rebound. For this purpose, we have developed an improved version of a chemiluminescence‐based urea sensor capable of measuring urea concentration in spent dialysate ( C D ) at 2‐min intervals. The correlation coefficient between the readouts of the sensor and the conventional enzyme‐ UV method was 0.97 and the sensor was not affected by 9 mmol/L uric acid, creatinine, or ammonia. Using the urea sensor, C D was measured as a function of dialysis time t during dialysis sessions for various blood flow rates. The urea reduction ratio based on the mass of the urea reduced ( m URR ) was estimated from the integrated value of C D ( t ). When in vitro urea concentrations are measured during a dialysis session in model blood (urea solution) at a constant volume ( V ) in a vessel, the plots of m URR were congruous with theoretical curves of conventional URR calculated based on the one‐pool model, and thus the accuracy of m URR was confirmed. On the other hand, in in vivo measurements of C D (t) during dialysis treatment for two patients, the plots of the m URR were not congruous with the theoretical curves of URR . Such a difference between URR and m URR was explained by the deviation of actual dialysis from the one‐pool model, and it was concluded that m URR might be accurate under any dialysis condition.