This study estimates the total removal of uric acid (TR_UA) by online UV absorbance measurements in the spent dialysate in two different dialysis centers in Estonia and Sweden. Sixteen dialysis patients were included. All dialysate was collected that gave the reference for TR_UA. Two regression models were investigated: one for each patient (UV1) and one for the entire material (UV2). TR_UA from the three methods was in the same order but showed a statistically significant difference when the UV2 model was built on data from both centers together. TR_UA, (n = 56) was (mean ± SD, µmol): 5,854 ± 1,377 for reference, 6,117 ± 1,795 for UV1 and 5,762 ± 1,591 for UV2. Six patients were monitored 1 year after the first study session, using the same models as the previous year, still having a nonsignificant difference. The results show the possibility of estimating TR_UA by using UV absorbance. The method appeared to be reliable also in long-term patient monitoring.

The present study contributes new information on the removal of uremic retention solutes during hemodialysis and on the origin of the optical dialysis adequacy monitoring signal.

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A need for dialysate-based, on-line, continuous monitoring systems for the control of dialysis efficiency and the prevention of dialysis-associated complications is arisen due to increasing number of dialysis patients and related treatment quality requirements. The aim of this study was to investigate the wavelength dependence between the the ultra-violet (UV) absorbance in the spent dialysate and the retained solutes removed during the hemodialysis in order to explain possibilities to estimate removal of the solutes by the optical dialysis adequacy sensor. Ten uremic patients, during 30 hemodialysis treatments, were followed at the Department of Dialysis and Nephrology, North-Estonian Regional Hospital. The dialysate samples were taken and analyzed with spectrophotometer to get absorbance spectra. The results confirm previous studies considering similarity for the UV-spectrum on the spent dialysate samples during a single dialysis session indicating presence of the same type of chromophores in the spent dialysate removed from the patient's blood for different patients groups. At the same time the highest correlation in the spent dialysate for urea, creatinine, potassium, and phosphate was obtained at the wavelength 237 nm that is a new finding compared to earlier results. The highest correlation between the UV-absorbance and uric acid in the spent dialysate was obtained at the wavelength 294 nm. Presence of at least two different wavelength ranges may add selectivity for monitoring several compounds. Our study indicates that the technique has a potential to estimate the removal of retained substances.

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