title: Near-infrared spectroscopy for measuring urea in hemodialysis fluids.
abstract: BACKGROUND
  Near-infrared spectroscopy is proposed as a method for providing real-time urea concentrations during hemodialysis treatments. The feasibility of such noninvasive urea measurements is evaluated in undiluted dialysate fluid.
  
  
  METHODS
  Near-infrared spectra were collected from calibration solutions of urea prepared in dialysate fluid. Spectra were collected over three distinct spectral regions, and partial least-squares calibration models were optimized and compared for each. Selectivity for urea was demonstrated with two-component samples composed of urea and glucose in the dialysate matrix. The 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 sound calibration models in the dialysate matrix. The combination spectral region 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 partial least-square factors. A second calibration model was established over the combination region from a series of solutions prepared with independently 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 cm(-1) spectral range. There was no significant decrease in SEP when the 4720-4600 cm(-1) calibration model was used to measure urea in real samples collected during actual hemodialysis.
  
  
  CONCLUSIONS
  Urea can be determined with sufficient sensitivity and selectivity for clinical measurements within the matrix of the hemodialysis fluid.
authors: Department of Chemistry and Optical Science and Technology Center, University of Iowa, Iowa City, IA 52242, USA.
authors: C V
authors: CV
authors: Eddy
authors: M A
authors: MA
authors: Arnold
mesh_terms: D005947:Glucose / Q000032:analysis; D015312:Hemodialysis Solutions / Q000737:chemistry*; D006801:Humans; D012680:Sensitivity and Specificity; D019265:Spectroscopy, Near-Infrared; D014508:Urea / Q000032:analysis*
chemical_list: D015312:Hemodialysis Solutions; D014508:Urea; D005947:Glucose