Chemical and Mineralogical Analysis of Ureteral Stent Encrustation and Associated Risk Factors

OBJECTIVE: To assess the burden and chemical and mineralogical composition of stent coating at both stent ends, with evaluation of associated risk factors. MATERIALS AND METHODS: A total of 40 consecutive patients submitted to ureteral-stent removal were considered. Stents were previously positioned for both urolithiasis and during the management of other urologic diseases and/or procedures. Mean indwelling time was 59.2 ± 7.5 days. ANALYTICAL PROCEDURES: Encrustations were submitted to chemical-mineralogical analysis as well as to their quantification. Quantification was achieved by measuring the weight of stent fragments before and after oxidative acid treatment to dissolve the deposited (both organic and inorganic) material. The analytical solution obtained by acid attack was used to acquire information on calcium and magnesium content with atomic-absorption spectroscopy. X-ray diffraction was used to determine the mineralogy of encrustations for a group of stent samples characterized by relatively high amounts of deposited material. RESULTS: The composition of encrustations at the proximal coil reflected the composition of stones in patients with urolithiasis. Whewellite was the more common encrustant. In a regression model, the variable mostly related to the burden of proximal encrustation was urolithiasis (P = .04), especially in frequent stone formers. At the distal coil, higher degrees of encrustation were related to urinary tract infection (P = .012) and patient's aging (P = .05), thus suggesting a possible association with a bladder outlet dysfunction. CONCLUSION: The present study highlighted some variables related to stent encrustation and seems to be the first one analyzing separately the two coils. Our outcomes suggest that the so-obtained risk factors have to be considered when positioning a ureteral stent.