Kidney Stone Analysis by Nicolet FTIR Spectrometer

The diagnostic usefulness of information regarding the chemical composition of renal stones has been recognized since the 1950s and has been significantly improved during last years [1—13]. So it is now possible to correlate the results of every analysis with the appropriate diagnosis and therapeutic regime. Nowadays, current physical and chemical methods available for urinary stones analysis are applied. But, no method is sufficient to provide all the clinically useful information on the structure and composition of the stones [9]. A combination of refined morphological and structural examination of stone with optical microscopy [3], complemented by compositional analysis using infrared spectroscopy of the core, cross-section, and surface of calculi [14—19] provides a precise and reliable method for identifying the structure and crystalline composition and permits quantification of stone components while being highly cost-effective. Stone component may be mineral, organic, or both. More than 65 different species (including 25 ones of exogenous origin) have been found in urinary calculi. Use of such morphoconstitutional studies leads to a classification of urinary stones in seven distinctive types and twenty-one subtypes [9] among calcium oxalate monohydrate (whewellite) and dihydrate (weddelite), phosphates, uric acid, urates, protein, and cystine (amino acids) calculi. The same chemical component may crystallize in different forms. Therefore a proper stone analysis has to identify not only the molecular species present in the calculus, but also the crystalline forms within chemical constituents. Most stones are of mixed composition and, among heterogeneous calculi, about 80 % are formed of a mixture of calcium oxalate and calcium phosphate in various proportions. By contrast, the presence of unique, but unusual compound (e.g. 2,8-dihydroxyadenine, xanthine, cystine, calcite) defines a specific type of urolithiasis. Quantitative evaluation of components is needed to provide full information. There are at least two approaches to the quantitative, or better, to the semiquantitative analysis of mixtures. PLS techniques yield highly precise result when the composition of an unknown material with predictable components present is restricted to a reasonably welldefined range. This procedure is less well suited to this application, because the range of concentration is very wide, and an unpredictable number of components is present. This technique which requires purchase of a relatively expensive PLS Software (Nicolet TQ Analyst) would be more difficult to use and has some other disadvantages (artifacts cannot be identified). Library Searching is the second possible method. Spectral library of real kidney stones must exist to use this method. An unknown sample spectrum is then compared to a number of library spectra and the most similar spectrum is found. The quality and quantity of the components of the most similar library spectrum is known. A match value close to 100 indicates that the sample consists of the same components in about the same ratio. The aim of this work was to create an automated FTIR analyzer of kidney stones. The idea was to provide a qualitative and quantitative analysis in one step and connect the analysis result directly to the information about diagnosis and therapy for the kind of stone found.