Characterization of urinary stones using Raman and Fourier transform infrared spectroscopy compared to a chemical colorimetric method

Introduction: Chemical-colorimetric methods for kidney stones identification are widely adopted in most routine laboratories due to low cost with no need of instrumental analysis. Actually, kidney stones are well characterized with the Fourier transform infrared spectroscopy combined with Attenuated Total Reflection (ATR/FT-IR) that allows quick identification of chemical compounds into solid samples. Furthermore, Raman spectroscopy is under investigation as a complementary technique to ATR/FT-IR. Methods: The comparison between chemical-colorimetric method and ATR/FT-IR and Raman spectroscopy has been performed evaluating standards (n=60) and urinary stones (n=89), after morphological and chemical characterization by Raman spectroscopy. Results: Identification rate of low quantities in standards (5% and 10% respectively) for the three methods were as follow: Chemical-colorimetric method, 20% and 40%; Raman spettroscopy, 87% and 90%; ATR/FT-IR, 53% and 63%. The comparison of the 89 urinary stones revealed that chemical-colorimetric method results differ from spectroscopic technique identifications particularly for oxalate ions, phosphate and uric acid (15 samples out of 89). The agreement between the investigated methods is more than 80% in kidney stones with one prevalent compound (56 samples). In the other samples characterized by two or more compounds (33 samples), discordant identifications between methods were evaluated and discussed. Discussion: ATR/FT-IR and Raman spectroscopy present many advantages in terms of identification of the most representative compounds of kidney stones; therefore, they represent a valid solution for a second level laboratory that receives a large number of samples and should examine them with the most adequate technological support.