Objectives: To determine the feasibility of near-infrared analysis for
quantitating urea, creatinine, and protein in urine. Practical advant
ages of this method include ease of sample presentation and the absenc
e of reagents or disposables. Design and Methods: The near-infrared me
thods were developed by first measuring the spectra of 123 different u
rine samples and, using independent clinical analyses, determining the
protein, creatinine, and urea levels in each. Calibration models rela
ting near-infrared spectroscopic features to those independently deter
mined concentrations were optimized, and each model then validated usi
ng a set of 50 additional samples. Results: Standard errors of calibra
tion were 14.4 mmol/L, 0.66 mmol/L, and 0.20 g/L, and standard errors
of prediction 16.6 mmol/L, 0.79 mmol/L, and 0.23 giL, respectively, fo
r urea, creatinine, and protein. Conclusions: Near-infrared urea quant
itation is as accurate as the reference method, enzymatic (urease) con
ductivity, used here for calibration. Creatinine analysis is slightly
less accurate relative to the reference (Jaffe rate) method; however,
these errors can be minimized by careful attention to factors affectin
g precision. The accuracy of the near-infrared protein analysis cannot
approach that of the reference method; nevertheless, the technique is
potentially useful for coarse screening and for quantifying protein l
evels above 0.3 g/L.