Online Uric Acid Concentration Estimation in Blood from Spent Dialysate Measurements Using an Optical Sensor

This study aimed to estimate concentration of uric acid (UA) in blood from online spent dialysate measurements during haemodialysis (HD) with an optical sensor non-invasively. Twenty-two patients on chronic (HD) were monitored during 88 treatment sessions, including HD and haemodiafiltration treatments. Pre- and post-dialysis blood samples and spent dialysate samples, from the drain outlet of HD machine, were collected during each session. HPLC analysis was used as a reference to determine UA concentrations in the samples. An optical sensor was connected to the drain outlet of the HD machine and ultraviolet light absorption of spent dialysate was measured online for each HD session at four different wavelengths. A linear interactions regression model was used to estimate UA concentrations in spent dialysate with the optical sensor based on the light absorption. Sensor estimated spent dialysate UA concentrations were highly accurate with standard error (SE) < 3.50 µmol/L and strongly correlated (R2 >= 0.983) to the actual UA concentrations of spent dialysate in the training and the test dataset. A linear regression model, using treatment settings and UA concentration determined with optical sensor, was employed to estimate concentration of UA in blood samples. Sensor estimated blood UA concentrations were similarly highly accurate (SE < 32.1 µmol/L) and strongly correlated (R2 > 0.95) to the actual UA concentrations of blood in the calibration and the validation dataset. In conclusion, this study showed that UA levels in blood can be estimated noninvasively with the optical sensor in real time, with higher accuracy than shown previously.