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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The aim of this study was to investigate the behaviour of uremic toxins and UV absorbance in respect to low and high flux dialyzers during hemodialysis treatments. Ten uremic patients were investigated using online spectrophotometry, with wavelength of 280 nm, over the course of 30 hemodialysis treatments. The polysulphone dialyzers were used. The taken dialysate and blood samples were analysed using standard biochemical methods and reversed phase HPLC. The chromatographic peaks were detected by a UV detector at wavelengths of 254 and 280 nm. Spiking experiments and UV spectra between 200-400 nm allowed to identify predominant uremic toxins in 5 chromatographic peaks identified as creatinine (CR), uric acid (UA), hypoxanthine (HX), indoxyl sulphate (IS), and hippuric acid (HA). Moreover, two persistent, but non-identified peaks, peak 1 (P1) and peak 2 (P2), were detected. There was no significant difference in the reduction ratio of uremic solutes and the UV absorbance between the low and high flux membranes. The reduction ratios, estimated by the total area of HPLC peaks at 254 nm and 280 nm in the serum and by the online UV absorbance at 280 nm, were closest to the removal of small water-soluble non-protein bound solutes urea, creatinine and uric acid. All studied uremic toxins and UV absorbance showed similar reduction for the low and high flux membranes during hemodialysis.

Several on-line methods have been developed to standardize the assessment of dialysis adequacy. Earlier studies have demonstrated that on-line monitoring of total ultra violet (UV) absorbance in spent dialysate can be utilized to follow continuously a single hemodialysis session. The aim of this study was to investigate the contribution of different compounds, acting as chromophores, to the UV-absorbance in the spent dialysate in order to explain origin of the cumulative and integrated UV-absorbance measured by the optical dialysis adequacy sensor.Four uremic patients, during 12 hemodialysis treatments, were followed by the optical dialysis adequacy sensor using the wavelength of 280 nm. The dialysate samples were taken and analyzed using reversed phase high performance liquid chromatography (HPLC). The total number of detected peaks from the HPLC gradient separation profiles measured at the wavelength 280 nm for the samples collected 10 min after the start of hemodialysis (Mean ± SD) was 38 ± 6. The relative contribution from the area of 10 main peaks to the total area of all detected peaks in percentage was 91.01 ± 2.52 %.The optical dialysis adequacy sensor provides continuous, on-line hemodialysis measurements and may immediately identify and alert to any deviations in the dialysis. Our study indicates that there exists a number of prevalent compounds that are the main cause of the cumulative and integrated UVabsorbance.