QUANTITATION OF PROTEIN, CREATININE, AND UREA IN URINE BY NEAR-INFRARED SPECTROSCOPY

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.