Urinary levels of amorphous urate crystals as a biological marker for occupational exposure to crystalline free silica

Introduction: Due to the obvious adverse effects of exposure to free crystalline silica and the high exposure level in silica-related occupations, the present study aimed at the investigation of renal symptoms in cement factory workers. 
Materials and methods: For this reason, 128 workers who were working cement factory with a determined occupational exposure to crystalline-free silica were selected as the case group, and 143 workers who were working in the Hamedan Province Rural Water and Wastewater company without being exposed to crystalline free silica were selected as controls. Various kidney- related parameters were evaluated and compared between the selected case and control groups. 
Results: The results of urine analysis between cases and control showed that there was a statistical difference between the cases and controls regarding Red Blood Cell (RBC), epithelial count, and bacteria (p<0.05). Moreover, the percentage of amorphous urate crystals of the exposed workers (cases) and control were 80.7% and 38.3%, respectively (p<0.001). The results of adjusted results showed that the odd presence of amorphous urate crystals among cases was 7.65 times of the control group (p<0.001). 
Conclusion: Our findings clearly showed that the level of urinary levels of amorphous urate crystals in silica-exposed individuals is higher than that of non-exposed individuals. Therefore, the presence of urinary amorphous urate crystals in exposed workers may be used as a cheap, non-invasive, and efficient method and urine biological maker for detecting silica exposure in silica-related industries.