Clinical Chemistry
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Clinical Chemistry 50: 175-181, 2004; 10.1373/clinchem.2003.025569
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(Clinical Chemistry. 2004;50:175-181.)
© 2004 American Association for Clinical Chemistry, Inc.

Point-of-Care Testing

Online Measurement of Urea Concentration in Spent Dialysate during Hemodialysis

Jonathon T. Olesberg1, Mark A. Arnold1,a and Michael J. Flanigan2

1 Optical Science and Technology Center and the Department of Chemistry, and
2 College of Medicine, The University of Iowa, Iowa City, IA 52242.

aAuthor for correspondence. Fax 319-353-1115; e-mail mark-arnold{at}uiowa.edu.

Background: We describe online optical measurements of urea in the effluent dialysate line during regular hemodialysis treatment of several patients. Monitoring urea removal can provide valuable information about dialysis efficiency.

Methods: Spectral measurements were performed with a Fourier-transform infrared spectrometer equipped with a flow-through cell. Spectra were recorded across the 5000–4000 cm-1 (2.0–2.5 µm) wavelength range at 1-min intervals. Savitzky–Golay filtering was used to remove baseline variations attributable to the temperature dependence of the water absorption spectrum. Urea concentrations were extracted from the filtered spectra by use of partial least-squares regression and the net analyte signal of urea.

Results: Urea concentrations predicted by partial least-squares regression matched concentrations obtained from standard chemical assays with a root mean square error of 0.30 mmol/L (0.84 mg/dL urea nitrogen) over an observed concentration range of 0–11 mmol/L. The root mean square error obtained with the net analyte signal of urea was 0.43 mmol/L with a calibration based only on a set of pure-component spectra. The error decreased to 0.23 mmol/L when a slope and offset correction were used.

Conclusions: Urea concentrations can be continuously monitored during hemodialysis by near-infrared spectroscopy. Calibrations based on the net analyte signal of urea are particularly appealing because they do not require a training step, as do statistical multivariate calibration procedures such as partial least-squares regression.




The following articles in journals at HighWire Press have cited this article:


Home page
 Nephrol Dial TransplantHome page
F. Uhlin, I. Fridolin, M. Magnusson, and L.-G. Lindberg
Dialysis dose (Kt/V) and clearance variation sensitivity using measurement of ultraviolet-absorbance (on-line), blood urea, dialysate urea and ionic dialysance
Nephrol. Dial. Transplant., August 1, 2006; 21(8): 2225 - 2231.
[Abstract] [Full Text] [PDF]


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