Toward Reagent-free Clinical Analysis: Quantitation of Urine Urea, Creatinine, and Total Protein from the Mid-Infrared Spectra of Dried Urine Films

摘要

Infrared (IR) spectroscopy offers an approach to clinical analysis that is conceptually very appealing. Whereas countless assays rely on the use of chemical agents to “recognize” the analyte of interest and to react with the analyte to produce specific color changes, IR-based analysis is founded on the rich IR absorption patterns that characterize the analytes themselves. These absorption patterns provide the basis to distinguish among the constituents and to separately quantify them. The most obvious distinguishing feature is that no reagents are required. In addition, IR-based analytical methods require very small sample volumes (typically microliters), show good precision over the entire physiological range, and are well suited for automation.Several previous studies have illustrated potential roles for IR spectroscopy in the clinical laboratory. For example, six serum analytes have been shown to be suitable for IR-based analysis, namely albumin, total protein, glucose, triglycerides, urea, and cholesterol (1)(2)(3)(4)(5)(6). Studies of amniotic fluid have yielded IR models to quantify the lecithin/sphingomyelin ratio and the surfactant/albumin ratio, establishing IR spectroscopy as an attractive option for the assessment of fetal lung maturity (7)(8).There are several approaches to IR-based analysis, with the first choice being whether to use the near-IR (750–2500 nm) or mid-IR (2.5–100 μm) spectral range. Near-IR spectroscopy has gained notoriety within the clinical chemistry community through the many efforts to develop a noninvasive blood glucose monitor based on this technology [see e.g., Refs.(9)(10)], and in that vein it has been shown that glucose concentrations can be recovered from the near-IR spectrum of native serum (3).The main reason for the focus on near-IR …