Removal of Urea, β2-Microglobulin, and Indoxyl Sulfate Assessed by Absorbance and Fluorescence in the Spent Dialysate During Hemodialysis

Abstract

In this study, simultaneous removal assessment of marker molecules from three uremic toxin groups was performed during different hemodialysis treatment modalities using optical characteristics of spent dialysate. Results from optical measurements were compared with the results from chemical laboratory. Ten chronic dialysis patients, mean age 59 ± 15 years, were included in the study during 40 hemodialysis sessions. Low-flux hemodialysis (HD), high-flux hemodialysis (HF), and postdilutional online hemodiafiltration (HDF) with different settings were used. The reduction ratio (RR) and total removed solute (TRS) of three uremic solutes were determined: small molecular weight urea, middle molecular β2-microglobulin (B2M), and protein-bound indoxyl sulfate (IS). Concentrations of these solutes in the spent dialysate were measured by laboratory (lab) and optical (opt) methods, in the serum by laboratory methods, and calculated RR values in percentage were compared accordingly. Total removed solute was obtained from the total dialysate collection (TDC) using lab and opt methods. The highest RR values were found for urea and B2M, and the lowest for IS. The difference between RR of lab and opt results estimated as mean accuracy (BIAS) was ≤8.1% for all three solutes. Good correspondence between TRS lab vs. opt was achieved, resulting in strong linear correlation values R from 0.727 for urea to 0.971 for IS. Accuracy for TRS values as BIAS ± standard error (SE), comparing lab vs. opt, showed no statistical difference for any of the observed uremic solutes (P > 0.05). The accuracy of the optical method was not influenced by the dialysis modality (HD, HF, and HDF).

Serum Levels and Removal by Haemodialysis and Haemodiafiltration of Tryptophan-Derived Uremic Toxins in ESKD Patients

“…The RR and TRS values behaved similarly for different dialysis modalities and settings for urea, IS and IAA as mean RR and TRS values were significantly lower for conventional low-flux dialysis than for other dialysis settings for all solutes (p < 0.001), which is in good relation with results of the previous studies [51,52]. However, Trp RR values were not influenced by dialysis modality.…”

Optical Method and Biochemical Source for the Assessment of the Middle-Molecule Uremic Toxin β2-Microglobulin in Spent Dialysate

“…A comparison of both UV absorbance and fluorescence spectra of untreated HDF dialysate with corresponding filtrates, containing solutes < 1kDa (Figures 5 and 7), as well as the corresponding comparison of HDF and LF HD spent dialysate strongly supports the idea that optical properties of dialysate provide a potential for on-line monitoring of eliminating not only small and protein-bound molecules, but also middle molecule uremic toxins from the blood of ESKD patients [29][30][31]. The highest absorbance in the short wavelength region of UV light could be expected in the light of present knowledge about the peptide nature and amino acid composition of the MM uremic toxins [35].…”

“…However, many recent publications have confirmed the essential role of middle molecule (MM) group of uremic toxins in pathology and mortality of ESKD patients [24][25][26][27][28]. Despite promising works exploring the correlation between optical properties of spent dialysate and MM molecules, the biochemical origin of the MM toxins' optical contribution to the optical signal has not yet been revealed [29][30][31]. Still, the optimization of the removal of MM uremic solutes has remained an unsolved problem in the treatment of ESKD patients [32].…”

Routine online assessment of dialysis dose: Ionic dialysance or UV‐absorbance monitoring?

“…UV‐A monitoring allows total urea removal and nPCR to be calculated, provided dialysate urea concentration measurements have been performed to determine the regression line between UV‐A and dialysate urea concentration for the considered patient 50 . Combining UV‐absorbance at several wavelengths and fluorescence in the spent dialysate allows to accurately estimate the removal of β2‐microglobulin (a middle molecule) and indoxyl sulfate (a protein‐bound molecule) 51 . However, the devices required are very complex and are not currently implemented in available hemodialysis machines.…”