Jana Holmar

Optical Method for Cardiovascular Risk Marker Uric Acid Removal Assessment during Dialysis

The aim of this study was to estimate the concentration of uric acid (UA) optically by using the original and processed ultraviolet (UV) absorbance spectra of spent dialysate. Also, the effect of using several wavelengths (multi-wavelength algorithms) for estimation was examined. This paper gives an overview of seven studies carried out in Linköping, Sweden, and Tallinn, Estonia. A total of 60 patients were monitored over their 188 dialysis treatment procedures. Dialysate samples were taken and analysed by means of UA concentration in a chemical laboratory and with a double-beam spectrophotometer. The measured UV absorbance spectra were processed. Three models for the original and three for the first derivate of UV absorbance were created; concentrations of UA from the different methods were finally compared in terms of mean values and SD. The mean concentration (micromol/L) of UA was 49.7 ± 23.0 measured in the chemical laboratory, and 48.9 ± 22.4 calculated with the best estimate among all models. The concentrations were not significantly different (P ≥ 0.17). It was found that using a multi-wavelength and processed signal approach leads to more accurate results, and therefore these approaches should be used in future.

Optical measurement of creatinine in spent dialysate

AIM The aim of the study was to develop an optical method for the estimation of creatinine (Cr) removal during dialysis using UV-absorbance. MATERIAL AND METHODS 29 hemodialysis patients on chronic 3-times-a-week hemodialysis were studied in 6 separate studies. Double-beam pectrophotometer was used for the determination of UV-absorbance in the collected spent dialysate samples. A single wavelength (SW) and a multi-wavelength (MW) model were developed using stepwise regression utilizing Cr values from the laboratory as the dependent parameter. The reduction ratio (RR) and total removed Cr (TRCr) were estimated. RESULTS For blood-Cr RRb (mean ± SD) was 60.9 ± 5.0% (calibration set) and 58.1 ± 6.0% (validation set), for SW UVabsorbance RR_SW was 61.5 ± 5.9% and 57.3 ± 6.0%, and for MW UV-absorbance RR_MW was 65.8 ± 5.8% and 61.7 ± 6.4% respectively. RR_SW and RRb were not statistically different. RR_MW was higher compared to RRb (p < 0.05). TRCr_lab was 13.8 ± 3.8 mmol, TRCr_SW 14.5 ± 2.5 mmol and TRCr_MW 13.8 ± 2.6 mmol, being not statistically different. CONCLUSION In summary, creatinine removal during dialysis can be estimated as reduction ratio and total removed creatinine with the UV-absorbance technique.

Utilization of UV Absorbance for Estimation of Phosphate Elimination during Hemodiafiltration

Background: Phosphate is an important factor in explaining the high progress of vascular calcification among dialysis patients. Today, phosphate concentration is measured in plasma on a regular basis. The aim of this study was to find out if it is possible to estimate total removed phosphate (TRp) in spent dialysate utilizing UV absorbance during hemodiafiltration. Methods: Eleven patients were monitored online with UV absorbance at 297 nm, three times during one week each (n = 33). Dialysate samples were taken at different times during treatment and from a collection tank to chemically determine phosphate concentrations. Two mathematical models (UVIND and UVGROUP) were tested to estimate TRp with supervision by UV absorbance and compared with TRp measured in the tank (reference). Results: High correlation between UV absorbance and phosphate concentration for each single patient and lower for the whole group together was found. TRp was (mean ± SD) 30.7 ± 7.3 mmol for the reference and 30.8 ± 8.2 and 29.1 ± 5.2 mmol for UVIND and UVGROUP, respectively (p > 0.05). Conclusion: This study demonstrates a novel possibility to estimate TRp based on linear relationship between online monitoring of UV absorbance and concentration of phosphate in spent dialysate.

Quantification of Indoxyl Sulphate in the Spent Dialysate Using Fluorescence Spectra

The aim of this study was to investigate the possibility to determine the amount of Indoxyl Sulphate (IS) in the spent dialysate using fluorescence spectra.

An optical method for serum calcium and phosphorus level assessment during hemodialysis.

Survival among hemodialysis patients is disturbingly low, partly because vascular calcification (VC) and cardiovascular disease are highly prevalent. Elevated serum phosphorus (P) and calcium (Ca) levels play an essential role in the formation of VC events. The purpose of the current study was to reveal optical monitoring possibilities of serum P and Ca values during dialysis. Twenty-eight patients from Tallinn (Estonia) and Linköping (Sweden) were included in the study. The serum levels of Ca and P on the basis of optical information, i.e., absorbance and fluorescence of the spent dialysate (optical method) were assessed. Obtained levels were compared in means and SD. The mean serum level of Ca was 2.54 ± 0.21 and 2.53 ± 0.19 mmol/L; P levels varied between 1.08 ± 0.51 and 1.08 ± 0.48 mmol/L, measured in the laboratory and estimated by the optical method respectively. The levels achieved were not significantly different (p = 0.5). The Bland-Altman 95% limits of agreement between the two methods varied from −0.19 to 0.19 for Ca and from −0.37 to 0.37 in the case of P. In conclusion, optical monitoring of the spent dialysate for assessing the serum levels of Ca and P during dialysis seems to be feasible and could offer valuable and continuous information to medical staff.

Beta2-microglobulin Measurements in the Spent Dialysate Using Fluorescence Spectra

The aim of this study was to measure the concentration of beta2-microglobulin (B2M) in the spent dialysate using optical method utilizing fluorescence spectra of the spent dialysate.

Estimation of removed uremic toxin indoxyl sulphate during hemodialysis by using optical data of the spent dialysate

The aim of this study was to explore the possibility to determine the amount of total removed Indoxyl Sulphate (TR_IS) during dialysis session, an optical method utilizing absorbance and fluorescence spectral data of the spent dialysate was used. Eight uremic patients from Linköping, Sweden and 10 from Tallinn, Estonia, were studied during dialysis treatments. Dialysate samples were taken during each treatment and analyzed at a laboratory. Fluorescence and absorbance spectra of the spent dialysate were measured with spectrofluorophotometer and spectrophotometer. The spectral values were transformed into IS concentration using multiple linear regression model from the total material noted as optical method (Opt). IS concentration was estimated using high-performance liquid chromatography (HPLC) method as a reference. TR_IS values were calculated. Achieved results were compared regarding mean values and SD and collated with the amount of total removed urea value (TR_Urea) for the same dialysis procedures. Mean TR value±SD (mg) for urea was 28 947±9 241; TR for IS was 151.4±87.3 estimated by HPLC and 149.4±84.9 estimated by Opt. The TR_IS values were not significantly different (p≤0.05). This study indicates, that it is possible to estimate TR_IS using only spectral values of the spent dialysate and the parameter can be used for quantifying the elimination of protein bound uremic toxins during the dialysis procedure.

New Optical Method for Estimation of Protein Bound Uremic Toxins Elimination

The aim of this study was to investigate the possibility to determine the amount of removed Indoxyl Sulphate (IS) during dialysis session. An optical method using fluorescence spectra was used.

Optical Estimation of Beta 2 Microglobulin during Hemodiafiltration - Does It Work?

Background: Currently, urea reduction seems to be the most widely used dialysis dose parameter. The aim of this study was to investigate the possibility to monitor beta 2-microglobulin (β2-M) elimination by utilizing the ultraviolet (UV) absorbance of spent dialysate. Methods: Blood and spent dialysate were collected during two weeks sessions in 8 patients, one week in hemodialysis (HD) and one in hemodiafiltration (HDF). Correlation analysis between UV-wavelengths and concentrations of solutes in spent dialysate was performed. The reduction ratio (RR) of concentrations in blood, dialysate and UV-absorbance were compared. Results: Differences between HD and HDF were discovered in wavelength correlation maxima for the solutes. Relative error in RR (%) was larger (p < 0.05) for β2-M than for the other solutes. The most reasonable explanation is that β2-M does not absorb UV-radiation; instead, the absorbance of surrogate substances is measured. Conclusion: A high correlation between UV-absorbance and β2-M can be achieved for HDF but not for HD. Still, UV-absorbance could perhaps be used in solely HDF mode for estimation of β2-M removal.

Optical Dialysis Adequacy Monitoring: Small Uremic Toxins and Contribution to UV-Absorbance Studied by HPLC

Uremic toxicity is described as a clinical picture resulting from impaired renal elimination and accumulation of uremic toxins in the body. Uremic toxins can be classified as small water-soluble compounds, middle molecules and protein-bound compounds. A long list of possible uremic toxins has been identified in recent decades. Under normal conditions these compounds are excreted by healthy kidneys. If kidney function fails, waste products accumulate in the blood and in the body. Dialysis treatment replaces some kidney functions through diffusion (waste removal) and ultrafiltration of fluid across a semi-permeable membrane, which is a thin layer of material with holes or pores of various sizes. A deeper understanding about the accumulation and removal mechanisms of the retained solutes during care of renal insufficiency is needed (Eloot, 2008; Eloot, 2007). This understanding would be especially informative with respect to predicting the mode of action of uremic toxins and their specific role in complications associated with dialysis or ureamia, but also with cardiovascular disease and inflammation (Vanholder, et al., 2008; Vanholder, 2003). The methods contributing to the identification, characterisation and evaluation of uremic retention solutes could be assessed in order to ensure dialysis adequacy and quality (Vanholder, 2005). The choice of the correct concentration of potential uremic toxins is still an unresolved issue (Vanholder, 2003). In everyday clinical practice, uremic components are not examined due to the measurement of most uremic components using the available laboratory methods being difficult and complex. A number of standard biochemical techniques are used in clinical laboratories, but there is no universal methodology. In addition, some chromatographic methods have been developed which explore uremic retention solutes. Dialysis efficiency and quality has been an important issue accompanied by optimisation and the best outcome of the treatment of chronic end stage renal disease for many years. In connection to this, online monitoring of the dialysis dose has been suggested as an effective way of improving treatment quality. The concept of online monitoring is based on the realtime measurement of chemical signals coming from the patient. This enables the early