Original ResearchThe systematic classification of urinary stones combine-using FTIR and SEM-EDAX

- Urinary stones were classified into eight types, including calcium oxalate, anhydrous uric acid stone, etc.
- The most common stone type was calcium oxalate stone, following by anhydrous uric acid stone.
- SEM revealed they exhibited a diversity of microstructures.
- X-ray energy spectrometer revealed they also presented distinct elemental composition and distribution.

BackgroundTo explore underlying mechanism of urinary stones formation, the composition and microstructure of urinary stones were analyzed systematically with a large sample study from China.Materials and methodsA total of 2437 urinary stones were obtained from the urology department at our Hospital. The composition of the stones was analyzed by Fourier transform infrared spectroscopy (FTIR). Meanwhile, the microstructure and element distribution were observed with scanning electron microscopy combined with element distribution analysis (SEM-EDAX).ResultsUrinary stones were classified into eight types, that were consisted of calcium oxalate stones (1301/2437, 53.39%), calcium phosphate stones (131/2437, 5.38%), anhydrous uric acid stones (434/2437, 17.81%), magnesium ammonium phosphate stones (12/2437, 0.49%), sodium urate stones (5/2437, 0.21%), brushite stones (4/2437, 0.16%), cystine stones (3/2437, 0.12%) and mixed stones (547/2437, 22.45%, ten subtypes were included). Under SEM, they displayed distinct microstructures: plank-like, brick-like, polyhedron or paliform crystals for calcium oxalate stones, similar sized echin-sphere or rough bulbiform or tree bark-like crystals for calcium phosphate stones, rotten-wood-like or petrous crystals for anhydrous uric acid stones, globular or gallet-like crystals for magnesium ammonium phosphate stones, sawdust-like crystals for sodium urate stones, broken-wood-like crystals for brushite stones, stacking hexagonal cystine crystals for cystine stones, and two or more of the above crystals for mixed stones. Meanwhile, they also presented distinct elemental composition and distribution by EDAX.ConclusionsUrinary stones can be classified into eight types, and exhibit a diversity of microstructure and elemental compositions in China. The formation process of different types of urinary stones may be diverse.