Analysis of Renal Stones by FT-IR Spectroscopy: A Helpful, Simple and Accurate Tool

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 December 2018.
Methodology: Infrared spectra of the urinary calculi were recorded in a Bruker IFS-25 FT-IR, Bruker
Alpha-T and in a Nicolet 380 FT-IR spectrophotometers. We included 542 urinary stones (331 from
men and 211 from women). The samples were obtained by spontaneous passage, shockwave
lithotripsy, ureteroscopy or percutaneous nephrolithotripsy.
Results: Calcium oxalate (both in pure or mixed samples) was detected in 396 cases (73.06%).
Anhydrous uric acid and struvite+apatite (7.56%) were both observed most frequently, followed by
carbonate apatite + amorphous Ca-phosphate (2.58%) and cystine (2.03%). 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. 73% of
recurrent urinary stones were of the same chemical composition.
Conclusion: FT-IR analysis of urinary calculi over a period of 25 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 (13.61%), 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.