Improved Optical Method for Measuring Concentration of Uric Acid Removed during Dialysis

Abstract

The aim of this study was to compare concentration measurements of uric acid (UA) removed during dialysis. Algorithms based on ultraviolet (UV) absorbance and 1^st derivate of UV-absorbance whereby single and multi-wavelength was used.

Ten uremic patients from Tallinn and ten from Linköping, during 30+40 haemodialysis treatments, were followed at the Departments of Dialysis and Nephrology at North-Estonian Medical Centre and at Linköping University Hospital. The dialysate samples were taken and analyzed by means of UA concentration at the chemical laboratory and with a double-beam spectrophotometer. UV absorbance and derivate of UV absorbance value on single or multi wavelength was transformed into UA concentration in the spent dialysate using the regression models from the total material, noted as UV-absorbance (UV_A _single and UV_A_multi) and the 1st derivate of UV absorbance (UV_D_single and UV_D_multi) method. Concentrations of UA from the different methods were finally compared regarding mean values and SD.

Mean concentration of UA were 52,40 ± 23,1 micromol/l measured at the chemical laboratory (UA_Lab), 52,39 ± 21,8 micromol/l determined by UV_A_single, 52,42 ± 22,4 micromol/ l determined by UV_A_multi and 52,4 ± 22,2 micromol/l determined by UV_D_single and 52,4 ± 22,9 micromol/l determined by UV_D_multi. The results of mean concentrations were not significantly different (p ≥ 0,95). The systematic errors were -0,7- -2,6% and random errors were 8 - 16 % using different methods. The systematic and random errors were significantly different (p < 0.05) between different algorithms indicating that the algorithm that uses multi wavelengths from derivative spectra enables more accurate UA estimation.

Our study indicates that the removed UA can be reliably and more accurately estimated by the UV_D_multi technique.