Research Article: Discolored Ureteral Stents: Findings in Urinalysis and Urine Culture

Date Published: April 7, 2015

Publisher: Public Library of Science

Author(s): Takashi Kawahara, Hiroshi Miyamoto, Hiroki Ito, Hideyuki Terao, Hiroji Uemura, Yoshinobu Kubota, Junichi Matsuzaki, Jayoung Kim.


Discolored ureteral stents are sometimes encountered in daily clinical practice; however, the mechanism(s) underlying the development of discolored ureteral stents remain unknown. In this study, we retrospectively analyzed the characteristics of discolored ureteral stents based on the results of a urinalysis and urine culture.

We identified a total of 26 patients with discolored ureteral stents and compared the findings in the urinalyses and urine culture in 21 discolored versus 45 non-colored ureteral stents.

The median and mean (±SD) duration of stenting time was 78.0 and 81.3 (± 21.3) days for the discolored ureteral stents and 69.0 and 74.9 (± 19.8) days for the non-colored ureteral stents, respectively (P = 0.25). The discolored ureteral stents were associated with a higher mean urine pH than the non-colored ureteral stents (mean: 6.4 vs 6.0, P< 0.05). There were no significant differences between the two groups in the RBC (P = 0.51) and WBC (P = 0.35) counts in the urinalyses. In addition, the rate of a positive culture in the patients with discolored stents [20 of 21 (95.2%)] was significantly (P <0.01) higher than that observed in the patients with non-colored ureteral stents [33 of 45 (73.3%)]. In this study, the subjects with discolored ureteral stents showed a significantly higher likelihood of having a positive urine culture and also demonstrated higher pH values in the urinalyses. However, no clear cut-off point to predict discoloration was indicated.

Partial Text

In 1967, Zimskind et al. first reported the use of silicon ureteral splints to relieve ureteral obstruction cystoscopically [1]. Since then, ureteral stenting has become a fundamental part of various urological procedures, including both open and endoscopic ureteral surgery, as well as the management of obstructing ureteral calculi, ureteral stricture, ureteropelvic obstruction and retroperitoneal tumors or fibrosis or after open or endoscopic ureteral surgery [2,3]. On the other hand, serious complications of ureteral stenting continue to occur, including encrustation, incrustation, migration and fragmentation [2–9].

During the same period, 26 discolored (black) and 69 non-colored ureteral stents were identified. The median (mean ± SD) indwelling time was 75.5 (84.6 ± 63.0) days for the discolored stents and 61.0 (61.9 ± 24.2) days for the non-colored stents (p = 0.01) (Table 1). In order to match the patients’ background factors, we analyzed cases with an indwelling time of 50 to 143 days in each group. Ultimately, 21 discolored ureteral stents and 45 non-colored ureteral stents with similar indwelling times were compared. The median (mean ± SD) indwelling ureteral stenting time was 78.0 (81.3 ± 21.3) days and 69.0 (74.0 ± 19.8) days in the discolored (coloring black) and non-colored stent groups, respectively (p = 0.25). In the cohort with discolored ureteral stents, 11 patients (52.4%) with stents had data for both a urinalysis and urine culture, while the remaining 10 patients (47.6%) without stents had such data. Similarly, among the 45 control cases, 17 (37.8%) and 28 (62.2%) subjects had data for a urinalysis and urine culture, with or without stents, respectively. The patient age and treated side were not significantly different between the groups (Table 2), whereas discolored ureteral stents were seen significantly more often in females.

We previously demonstrated that ureteral stent encrustation correlates with the indwelling time and that discolored stents more frequently tend to be encrusted [2]. In the present study, the patients with discolored ureteral stents were also shown to have a longer indwelling time, supporting previous findings[10]. More importantly, our current analysis showed that the patients with discolored ureteral stents had significantly higher rates of positive urine cultures and higher pH values on the urinalyses compared to that observed in the patients with non-colored ureteral stents. Discolored ureteral stents are frequently detected, whereas few urethral balloon catheters show heavily black discoloration. We speculate that this difference is due to the opacity of ureteral stents, which makes it easy to visualize the stents on X-ray films [2].