Observation and identification of autofluorescent urine crystals may be linked to a sign of urolithiasis.

Urolithiasis is a common disease of the urinary system. Its recurrence rate is high and may increase medical expenses. Urine stones are composed of urine crystals and other impurities. We discovered the existence of autofluorescence in some of the urine crystals, especially in urolithiasis patients. The fluorescent molecule existed in urine crystals was verified and identified. We have applied micro-Raman and fluorescence microscopy to classify the urine crystals, used confocal laser scanning microscopy (CLSM) to examine the 3D images and spectra of autofluorescence in crystals, used Fourier-transform infrared spectroscopy (FTIR) and mass spectrometry (MS) to identify the type of fluorophore in the autofluorescent urine crystals in urine. Riboflavin was identified as one of the major fluorophores in these autofluorescent urine crystals. The prevalence rates of the autofluorescent crystals in urolithiasis patients and subjects without the history of urolithiasis were to gather statistics. We observed that 80% of urolithiasis patients had autofluorescent crystals. Contrastingly, such crystals existed in only 7% of subjects without the history of urolithiasis. The presence of autofluorescent urine crystals may be linked to a sign of urolithiasis.