The analysis of peculiar urinary (and other) calculi: an endless source of challenge.

The exact composition of calculi is clinically important, but many specimens are not examined, with resultant loss of important information. We describe the incidence and nature of false stones, peculiar calculi and crystals growing on surprising materials. We studied 3100 calculi (97% urinary, 2% digestive and 1% others). Fourier transform infrared spectroscopy was used to identify calculi by detailed comparison with libraries of reference spectra. We also used UV-visible spectroscopy, nuclear magnetic resonance and gas chromatography-mass spectrometry for specific situations. Among 3100 calculi, 154 (5%) had an unusual composition; 101 specimens (3.3%) were false calculi or artifacts, 31 (1%) contained drugs or metabolites and 22 (0.7%) corresponded to crystallizations around other materials. The findings contribute to immediate patient management and to advances in scientific and medical knowledge. We conclude that the analysis of all calculi must be carried out, to determine their composition, and an efficient strategy must be used.