Near-infrared spectroscopy for measuring urea in hemodialysis fluids

Background: Near-infrared spectroscopy is proposed as a method for providin g real-time urea concentrations during hemodialysis treatments. The feasibi lity of such noninvasive urea measurements is evaluated in undiluted dialys ate fluid. Methods: Near-infrared spectra were collected from calibration solutions of urea prepared in dialysate fluid. Spectra were collected over three distin ct spectral regions, and partial least-squares calibration models were opti mized and compared for each. Selectivity for urea was demonstrated with two -component samples composed of urea and glucose in the dialysate matrix. Th e clinical significance of this approach was assessed by measuring urea in real hemodialysate samples. Results: Urea absorptions within the combination and short-wavelength, near -infrared spectral regions provided sufficient spectral information for sou nd calibration models in the dialysate matrix. The combination spectral reg ion had SEs of calibration (SEC) and prediction (SEP) of 0.38 mmol/L and 0. 26 mmol/L, respectively, over the 4720-4600 cm(-1) spectral range with 5 pa rtial least-square factors. A second calibration model was established over the combination region from a series of solutions prepared with independen tly variable concentrations of urea and glucose. The best calibration model for urea in the presence of variable glucose concentrations had a SEC of 0 .6 mmol/L and a SEP of 0.4 mmol/L for a 5-factor model over the 4600-4350 c m(-1) spectral range. There was no significant decrease in SEP when the 472 0-4600 cm(-1) calibration model was used to measure urea in real samples co llected during actual hemodialysis. Conclusions: Urea can be determined with sufficient sensitivity and selecti vity for clinical measurements within the matrix of the hemodialysis fluid. (C) 2001 American Association for Clinical Chemistry.