Part II Urinary calculus analysis

Quantitative assessment of urinary calculus (renal stone) constituents by infrared analysis (IR) is hampered by the need of expert knowledge for spectrum interpretation. Our laboratory performed a computerized search of several libraries, containing 235 reference spectra from various mixtures with different proportions was performed. Library search was followed by visual interpretation of band intensities for more precise semi-quantitative determination of the composition. We tested partial least-squares (PLS) regression for the most frequently occurring compositions of urinary calculi. Using a constrained mixture design, we prepared various samples containing whewellite, weddellite and carbonate apatite and used these as calibration set for PLS regression. The value of PLS analysis was investigated by the assay of known artificial mixtures, and selected patients' samples from which the semiquantitative compositions were determined by computerized library search followed by visual interpretation. Compared with this method, PLS analysis was superior with respect to accuracy and necessity of expert knowledge. Apart from some practical limitations in data-handling facilities, we believe that PLS regression offers a promising tool for routine quantification, not only for whewellite, weddellite and carbonate apatite, but also for other compositions of the urinary calculus. INTRODUCTION At present, >95% of all patients with urolithiasis are successfully treated with extracorporal shock wave lithotripsy [ESWL] in combination with intracoporal methods (1) for in situ calculi fragmentation. For patients with urinary stones in the ureter the percentage of success with ESWL treatment is <95%. Because of the high frequency of stone recurrence, which amounts to ~50% after 10 years (1), and limitations that exist for manipulative surgical intervention, there is increasing need for causal therapy. It is therefore important to be informed about the composition of the urinary calculi. In contrast to classical surgery for extracting renal calculi from the urinary tract, ESWL is hindered by the fact that often many calculi fragments are lost for further analysis. Since the introduction of ESWL in our hospital, ~3 years ago, we have found that, because of insufficient material, the composition of 34% of the urinary calculi presented to our laboratory could not, or only partly be determined with the classical wet chemical procedure. Infrared analysis (IR) of urinary calculi does not have this disadvantage. Using the KBr disk technique, samples as small as 1 mg can be analyzed (2). Other advantages of IR analysis over wet chemical analysis are higher speed, better reproducibility, and uniform sensitivities for all components (3). For …