Infrared Spectroscopic Analysis of Urinary Calculi: A Retrospective Study in Argentinean Patients

Aims: To investigate, by infrared spectroscopy (FT-IR), the chemical composition of urinary calculi obtained from patients of Buenos Aires, Argentina.

Duration of Study: The composition of the urinary calculi was evaluated in a retrospective study from March 1993 to September 2013.

Methodology: Infrared spectra of the urinary calculi were recorded in a Bruker IFS-25 FT-IR and in a Nicolet 380 FT-IR spectrophotometers. We included 440 urinary stones (286 from men and 154 from women). The samples were obtained by spontaneous passage, shockwave lithotripsy, ureteroscopy or percutaneous nephrolithotripsy mainly from patients treated at Hospital de Clínicas, University of Buenos Aires.

Results: Calcium oxalate (both in pure or mixed samples) was detected in 326 cases (74.09%). Anhydrous uric acid (8.41%) was observed most frequently, followed by struvite (2.05%) and cystine (2.50%). For some chemical compounds, a significant gender-related difference was found. Applying the second derivative spectra allowed to distinguish between the presence of whewellite, weddellite and their mixture. More than 70% of recurrent urinary stones were of the same chemical composition.

Conclusion: FT-IR analysis of urinary calculi over a period of 20 years gave an outlook of the prevalence of certain stone components in patients from Buenos Aires, Argentina, which in some cases were found to be gender-related. The results obtained are in accordance with statistics from other industrialized countries, except for uric acid (15.93%), even pure or combined in other forms, which was more frequent than the world prevalence (up to 10%). FT-IR spectroscopy combined with the second derivative method of analysis proved to be a powerful tool to discriminate mixed oxalates whose composition only differed in one water molecule.