Grand Journal of Urology
E-ISSN : 2757-7163

The Impact of Ureterenoscopic Stone Removal Timing on Kidney Functions: A Retrospective Analysis of 137 Patients in a Single Center
Ahmet Semih Guleser1, Mert Ali Karadag1
1Department of Urology, University of Health Sciences, Kayseri City Education and Research Hospital, Kayseri, Turkey
DOI : 10.5222/GJU.2021.53825
Pages : 096-100


Objective: To investigate the effect of ureterorenoscopic stone removal timing on kidney function in unilateral ureteral stones.

Materials and Methods: Hundred and eighty-seven patients included in the study were divided into two groups: 98 patients who underwent surgery ≤14 days after the stone diagnosis constituted the Early Surgery Group and 39 patients who were operated >14 days after the stone diagnosis comprised the Late Surgery Group. Preoperative serum levels of creatinine, blood urea nitrogen (BUN), and glomerular filtration rates (GFR) were recorded for the patients in both groups. In the postoperative first month, serum creatinine, BUN, and GFR were again recorded and compared with the preoperative values.

Results: The mean preoperative serum creatinine, GFR, and BUN levels in the Early Surgery Group were 1.25 ± 0.65μmol/L, 80.04 ± 33.6ml/min/1.73m2, and 50 ± 16.6mmol/L, respectively. A decrease was observed in serum creatinine (0.82 ± 0.22μmol/L, p< 0.001) and BUN (14.08 ± 7.25mmol/L, p< 0.001) levels one month after surgery, whereas GFR increased (105.33 ± 21.6ml/min/1.73m2, p< 0.001). In the Late Surgery Group, postoperative levels of serum creatinine (0.94 ± 0.33 vs. 0.95 ± 0.30μmol/L, p= 0.102), and BUN (17.38 ± 9 vs. 17.92 ± 8.8mmol/L, p= 0.283), increased minimally, also a minimal decrease was observed in GFR (95.15 ± 27.3 vs. 93.77 ± 24.3ml/min/1.73m2, p= 0.338) without any statistically significant difference.

Conclusion: We believe that surgical treatment should be planned within two weeks at the latest, as prolonged obstruction may result in kidney damage.


Worldwide, the prevalence of urinary system stone disease has been reported to vary between 1% and 20% [1]. Urinary system stones are treated according to their size, their anatomical location, and the complications they cause. Treatment options for ureteral stones include observation, medical expulsive therapy (MET), extracorporeal shock wave lithotripsy (ESWL), percutaneous antegrade ureteroscopy, retrograde ureteroscopy, and open or laparoscopic ureterolithotomy [2]. The treatment alternative chosen will depend on the location and size of the stone, the available technology, the treatment costs, the surgeon"s experience and the patient"s preference [3].

A meta-analysis has revealed that 68% of stones smaller than 5mm can pass spontaneously. This rate decreases to 47% for stones 5–10 mm in size [4]. The location of the stone is also an important factor in the possibility of spontaneous passage; 48% of proximal ureteral stones, 60% of middle ureteral stones, and 75% of distal ureteral stones may pass spontaneously [5]. For small ureteral stones, when there is no sign of infection and when the symptoms can be controlled, waiting for the stone to pass spontaneously is a good option. This approach also protects the patient from invasive surgical procedures and unnecessary costs. MET is an effective treatment approach for this patient group [6]. The MET method should not be used for stones larger than 10 mm [7].

It is still unclear exactly how long the waiting period will be between observation or MET and spontaneous stone passage. According to various studies, this period usually ranges from two to six weeks [8,9]. In patients with complete renal obstruction, urinary diversions may save kidney functions within a week, but, even if the obstruction is resolved, kidney functions may not recover for longer periods [10].

In this study, we aimed to evaluate the effects of ureteorenoscopic stone removal on kidney function in unilateral ureteral stones.

Materials and Methods

Patient Selection
Local ethics committee approval was obtained prior to study (approval number: 2021/385). This retrospective study analyzed data from 259 patients, who underwent URS for unilateral ureteral stones at Kayseri City Hospital between June 2017 and December 2020. Patients were excluded from the study if their serum creatinine values, and glomerular filtration rate (GFR) were unknown during the postoperative period, if computed tomography had not been used to diagnose their unilateral ureteral stones, if their GFR measures were ≤ 60, or if their stone sizes were > 10mm. The patients for whom the location and size of the stone could not be determined on preoperative radiological imaging (n:44), patients with stones larger than 10 mm (n:30), cases with GFR below 60 ml/min/1.73 m2 (n:27) and 21 patients with missing data were excluded from the study. In total, 137 patients were included in the study.

Study Design
The sampled patients were divided into two groups: those who underwent surgical intervention at ≤14 days (Early Surgery Group) and at >14 days after stone diagnosis (Late Surgery Group). Although there are studies stating the duration of observation and MET treatments between two and six weeks [8,9], we determined 14 days as the cut- off value in our study. Preoperative levels of serum creatinine, blood urea nitrogen (BUN), and glomerular filtration rate (GFR), location of stones in the ureters, the degree of hydronephrosis, age, gender of the patients, and time of diagnosis were recorded. The GFR was calculated for each patient based on the modification of Diet in Renal Diseases Study Formula (GFR=186 * [serum creatinin] - 1.154 X [age] – 0.203 [if female] * 0.742 [if African American] * 1.212). The severity of hydronephrosis was graded according to the anteroposterior diameter of the renal pelvis as follows: Grade 1 ( 5-10 mm), Grade 2 (10-15 mm), Grade 3 (15-20 mm), and Grade 4 (>20 mm). In the postoperative first month, serum creatinine, BUN, and GFR were again recorded and compared with the preoperative values.

Statistical Analysis
Data were analyzed using the Statistical Package for the Social Sciences (SPSS) for Windows, version 25.0 (IBM SPSS, Armonk, NY, USA). Normal distribution of the continuous variables was analyzed using the Shapiro–Wilk test and histograms. Continuous variables with normal distribution were expressed as mean ± standard deviation (SD). In independent groups, the continuous variables with normal distribution were compared using Student's t test. Identification rates were also compared using Pearson's chi-squared test. A p-value of <0.05 was considered significant.


In total, 137 (98 in the Early Surgery Group and 39 in the Late Surgery Group) patients were sampled. The mean age of the 96 patients in the Early Surgery Group was 43.62 ± 13.9 years including 38 (39.6%) female, and 58 (60.4%) male patients. The mean age of the 39 patients in the Late Surgery Group was 46.46 ± 13.7 years; including 12 (30.8%) female, and 27 (69.2%) male patients. In the Early, and Late Surgery Groups mean time intervals between the stone diagnosis and surgery were 5.4 ± 3.11, and 27.79 ± 15.35 days, respectively (p< 0.000). Table 1 presents the participants" demographic and clinical data. A decrease was observed in serum creatinine (0.82 ± 0.22μmol/L, p< 0.001) and BUN (14.08 ± 7.25mmol/L, p< 0.001) levels one month after surgery and the GFR increased (105.33 ± 21.6ml/ min/1.73m2, p< 0.001) in the Early Surgery Group. Table 2 presents the pre- and postoperative parameters for the Early Surgery Group. In the Late Surgery Group, postoperative serum creatinine levels increased minimally (0.94 ± 0.33 vs. 0.95 ± 0.30μmol/L, p= 0.102), but GFR decreased (95.15 ± 27.3 vs. 93.77 ± 24.3ml/min/1.73m2, p= 0.338). Although there was an increase in BUN (17.38 ± 9 vs. 17.92 ± 8.8mmol/L, p= 0.283) values, the intergroup different was not statistically significant. Table 3 depicts the pre- and post-operative parameters for the Late Surgery Group.

Table 1: Demographic and clinical characteristics of the patients

Table 2: Pre- and postoperative serum levels and glomerular filtration rates of the patients in the Early Surgery Group

Table 3: Pre- and postoperative serum creatinine levels and glomerular filtration rates of the patients in the Late Surgery Group


Urinary stone disease is an important public health problem in both adults and children. Recurrence is seen in one out of every three patients with urinary stone [11]. Urinary system stones may cause damage to the nephrons. Recurrent stones may lead to the development of a non-functioning kidney as an end-stage complication [12]. As a subgroup of urinary systems stones, ureteral stones can ensue in renal damage by causing ureteral obstruction [13]. Application of diversion in the first week after complete ureteral obstruction provides almost complete recovery of renal functions. While partial improvement was observed in renal functions in the diversions performed until the 12th week, the renal functions did not recover after urinary diversions performed after the 12th week [10]. In a study conducted in rabbits, blood perfusion had decreased in the first period in the obstructed kidney, there was a sharp rebound after a few days and then decreased again. The average rebound time in blood flow was 7.2 days [14]. Normally, it is accepted that a single morphologically and physiologically normal kidney is sufficient to perform all renal functions [15]. Therefore, unilateral ureteral obstructions do not usually cause renal dysfunction in healthy individuals. However, many patients may have abnormal renal function test results with normal contralateral kidney due to unilateral obstruction [16]. Similarly, although the contralateral kidneys of the patients were morphologically normal in our study, improvement in renal function tests was observed in patients in the Early Surgery Group.

Patients with unilateral obstruction and normal functioning contralateral kidneys demonstrate more frequently urinary dysfunction than patients with a single kidney [17]. In a prospective observational study on 152 patients; acute renal damage has been reported in 37 (29%) of 126 patients with unilateral ureteral stones. Renal recovery has been reported in 72% -100% of the cases after ureteral stone surgery. It has been shown that early intervention is associated with higher recovery rates [18]. Likewise, improvement in renal functions was observed in our Early Surgery Group, whereas renal recovery was not observed in the Late Surgery Group.

Although noninvasive treatments such as observation and medical expulsive therapy (MET) are being used in the treatment of ureteral stones, there is no consensus on duration of these treatments, and selection of eligible patients. In the studies in the literature, MET was generally performed between 2 and 6 weeks prior to surgery. MET has been accepted to have unsuccessful outcomes for varying periods of time depending on the center administering the treatment [9]. Lack of a consensus on appropriate timing for uterorenoscopy or urinary diversion has led to different approaches. In our study, a serious improvement was observed in kidney functions in the group of patients who were selected for early surgical treatment, while any change in renal functions was not detected in the Late Surgery Group. Delaying surgical management of an ureteral stone for MET or any other reason may result in renal damage. This important issue should be taken into consideration when treating patients using alternatives other than urinary diversion.

The weaknesses of our study can be listed as its retrospective design, insufficient number of patients, and the inability to standardize the groups in terms of their renal functions. Although prospective randomized studies on this issue are required, delaying surgical treatment may cause ethical problems. Application of different treatment approaches to standard groups under the same conditions is not accepted by the local ethics committee. For this reason, our study was designed retrospectively. Although the groups in our study were similar in terms of age, gender, stone location, degree of hydronephrosis, blood urea level, a significant intergroup difference was found between them in terms of preoperative serum creatinine levels and glomerular filtration rates. It was thought that as the renal dysfunction worsened, clinicians might have drifted away from observation and medical treatment which explains why the groups could not be standardized in this respect. There are not enough studies in the literature regarding the timing of surgery in ureteral stones. Therefore, multicenter studies in larger patient groups are required.


Treatment methods such as observation and MET applied to patients in order to reduce the morbidity caused by surgery do not eliminate obstruction. In addition, there is no consensus yet on how long these treatments will be applied. We believe that surgical treatment should be planned within two weeks at the latest, as prolonged obstruction may result in kidney damage.

Ethics Committee Approval: The study was approved by the Ethics Committee of Kayseri City Education and Research Hospital (Approval Date, and Registration Number: 04.29. 2021/385).

Informed Consent: An informed consent was obtained from all the patients.

Publication: The results of the study were not published in full or in part in form of abstracts.

Peer-review: Externally peer-reviewed.

Authorship Contributions: There is not any contributions who may not be listed as authors. Concept – A.S.G., M.A.K.; Design – A.S.G., M.A.K.; Supervision – A.S.G., M.A.K.; Resources – A.S.G., M.A.K.; Materials – A.S.G., M.A.K.; Data Collection and/or Processing – A.S.G., M.A.K.; Analysis and/ or Interpretation – A.S.G., M.A.K.; Literature Search – A.S.G., M.A.K.; Writing – A.S.G., M.A.K.; Critical Review – A.S.G., M.A.K.

Conflict of Interest: The authors declare that they have no conflict of interest.

Financial Disclosure: The authors declare that this study received no financial support.


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Keywords : ureterorenoscopic stone removal, ureteroscopy, ureter stone, kidney function, medical expulsive therapy

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