Correlation Between Urinary Osteopontin Concentration and the Mineral Content and Composition of Kidney Stones

Background and Objective: Information about the type of kidney stones is important for informed therapeutic decisions and the prevention of urolithiasis. Urinary stones are heterogeneous, and their elemental composition and crystal structure vary between patients. The formation of urinary stone deposits depends, among other things, on physiological conditions, the concentration of promoters and inhibitors of crystallization, and proteins found in the urine. The aim of this study was to determine differences in urine osteopontin (OPN) levels between groups of different stone-formers. Methods: Urinary stone specimens (n = 44) were acquired during elective endoscopic procedures. Specimens were divided into subgroups by k-means cluster analysis depending on calcium and phosphorus concentrations. The concentration of urine OPN was determined and compared for each subgroup and the control group. Results: Cluster analysis divided the deposits into three clusters. Cluster 1 contained mainly calcium oxalate deposits; Cluster 2 contained uric acid deposits; Cluster 3 contained deposits with a high content of calcium phosphate. Urine OPN concentration in CaP stone-formers (5.77 ng/mL) differed significantly from those of controls (17.05 ng/mL, p = 0.013) and CaOx stone-formers (15.31 ng/mL, p = 0.048). Conclusions: The concentration of urine OPN varies depending on the elemental composition of renal calculi. The lowest concentration of OPN was determined in the group of patients with a high content of calcium phosphate in the deposits.