Bladder Stone Composition in Jiangsu Region of China: Results from 421 Stone Analyses Open Access

Bladder stone is a rare disease accounting for 5% of all urinary calculi [1, 2]. Primary bladder stones are relatively common in children and can be caused by dietary factors [3, 4]. Secondary bladder stones are associated with incomplete bladder emptying, which can increase the likelihood of both stone formation and retention [5]. Migratory bladder stones form in the upper urinary tract before moving into the bladder [6]. The composition of bladder stones may be affected by a variety of factors, including dietary patterns, geographic location, socioeconomic status, infections, anatomical abnormalities of the urinary tract, and metabolic disorders [6, 7]. Understanding the stone composition can help guide the best therapeutic approach for each patient.

Our center is one of the largest urinary stone management institutions in East China. The present retrospective study was conducted to analyze the composition of bladder stones in East China, primarily in Jiangsu province. The aim of this study was to analyze the relationships of gender, age, and clinical characteristics with stone composition.

From January 2014 to March 2023, patients diagnosed with bladder stones at our center were included in this study. A total of 421 bladder stone specimens were collected, all of which were obtained intraoperatively, including transurethral cystolithotripsy, and laparoscopic or open surgery. Clinical information and demographic data were collected from all patients. Online supplementary Table 1 (for all online suppl. material, see https://doi.org/10.1159/000542255) shows the demographic data of all the enrolled patients.

The predominant stone components were recorded and classified according to Mayo Clinic stone classification practices and EAU guidelines [8], including calcium oxalate (CaOx) stones, calcium phosphate (CaP) stones, uric acid (UA) stones, infection stones, and cystine stones.

All calculi were analyzed by Fourier transform infrared spectroscopy at our center. First, the stones were washed and air-dried naturally or dried at 50°C. Next, 1 mg of the powdered stone specimen was mixed with 200 mg of dried potassium bromide. The mixture was then placed in an agate mortar and ground thoroughly until a fine powder with a diameter of less than 2 μm was formed. Afterward, the mixed powder was transferred into a mold and a tablet press machine was used to prepare the semitransparent thin slices at a pressure of 10–15 MPa for tests with an infrared spectroscopy analyzer. The instruments used in this study included the SUN-3G Intelligent Stone Analyzer from Dingshun (JiNan) Medical Equipment Co., Ltd.

All parameters were presented as frequency or mean ± standard deviation. Chi-square test was conducted to analyze differences in categorical variables between the groups. One-way ANOVA was adopted to compare the blood chemical values among diverse stone groups. All statistical analyses were carried out using SPSS 13.0. p value <0.05 was considered statistically significant.

A total of 421 patients with bladder stones were analyzed in our study, of which 402 (95.6%) were males, with a male-to-female ratio of 21:1. The age of patients ranged from 3 to 92 years, with an average of 66.90 ± 13.24 years. Among them, 322 patients were over 60 years old (online suppl. Table 1). All patients underwent surgical treatment. A total of 415 patients underwent transurethral cystolithotripsy, 5 patients underwent open cystolithotomy, and 1 patient underwent percutaneous cystolithotripsy.

Of the 421 bladder stone specimens, 161 (38.2%) were composed of a single component, 140 (33.3%) were comprised by two components, and 120 (28.5%) consisted of three or more components (Table 1). CaOx was detected in 279 (66.3%) of the total stones, CaP in 218 (51.2%) stones, and UA in 149 (35.4%) stones. CaOx was the main component in 181 (43.0%) stones, while UA was the main component in 149 (35.4%) stones. The remaining main stone compositions included infection stone 38 (9.0%), CaP 51 (12.10%), and cystine 2 (0.5%) (Table 2).

To investigate the impact of age on stone composition, patients were categorized into four groups, including 1–20 years, 19–40 years, 41–60 years, and over 60 years. The highest stone prevalence appeared in patients over 60 years old and increased progressively with age. Among patients aged over 60 years, the most common stone composition was CaOx, followed by UA, CaP, and infectious stones. There was a significant difference in the incidence of bladder stones between males and females. The most common type of stones in male patients is CaOx, followed by UA, CaP, infectious stones, and cystine stones. In females, the most common type of stones was infectious stones, followed by CaOx and CaP stones, and UA stones. For patients with UA stones, they were more likely to have lower urinary pH levels. Additionally, patients with infection stones displayed a higher incidence rate of urinary tract infections (UTIs) than those with other types of stones (Table 3).

The CT scans assessed stone size (mm), stone volume (mm³), and the number of stones. Stone volume was the sum of each stone volume (0.52 × length × width × height). We found that infectious stones had the largest volume, followed by UA stones. UA stones are more likely to develop multiple stones compared to other compositions (Table 3).

Compared with patients with other types of stones, patients with UA stones showed higher average serum UA and creatinine levels. However, there were no significant differences in other serum variables such as calcium, potassium, phosphorus, calcium, and sodium, as shown in Table 4.

The incidence of urolithiasis shows a steadily increasing trend in the last few decades. Although bladder stones account for only a small proportion of urolithiasis, they still affect the health of elderly men [1, 9]. In this study, we retrospectively analyzed the records of bladder stone composition and the relationships with clinical data in our center over the past 10 years.

The incidence of bladder stones is indeed higher in male patients than in females. This is primarily due to the anatomical differences in the male urinary system, making male patients more susceptible to lower urinary tract obstructions [10]. In the present study, the male-to-female ratio of bladder stone prevalence was 21:1, which exceeds the ratios reported in previous studies [7, 11].

In our study, although CaOx stones were the most common component (43.0%), the results were significantly lower than the data reported in previous national urine stone composition analyses, which found that CaOx stones accounted for approximately 60.7% of cases [7]. UA stones are second only to calcium-containing stones in terms of the prevalence. In our research, UA stones were observed in 35.4% of cases, and such figure was apparently higher than previous data (16.1%) [7]. Urinary pH is a pivotal factor for UA crystallization [12]. In this study, patients with UA stones were more likely to have lower urine pH values. At the same time, UA stones were found to be associated with elevated serum creatinine and UA levels. This suggests a potential association between UA stone formation and the impaired kidney function or increased UA production. The elevated serum creatinine levels may indicate the reduced kidney function, which can contribute to UA accumulation and UA stone formation. Similarly, higher UA levels in the blood can increase the risk of UA stone formation, as UA can crystallize and precipitate in the urinary tract. These findings highlight the importance of monitoring serum Cr and UA levels in individuals at risk of UA stone formation. Urine alkalinization can reduce the formation and recurrence of UA stones, and decrease the chances of a secondary surgery. We also found that UA stones are more likely to form multiple stones compared to stones of other composition. This is because UA is more prone to precipitation in an acidic environment, leading to the simultaneous formation of crystallization cores at multiple sites in the urine, resulting in the appearance of multiple cores [13].

In accordance with other reports, our study discovered a higher proportion of infection stones among females than males [14]. Indeed, while the overall incidence of bladder stones is lower in females, it is noteworthy that infectious stones are the most common main component of bladder stones in females. Infections, particularly UTIs, can contribute to the formation of stones in the bladder. The female anatomy, with a shorter urethra, makes women more susceptible to UTIs, which can lead to the deposition of infectious agents and the subsequent development of stones. In our study, the volume of infectious stones is larger compared to stones of other compositions, which may be related to the rapid growth rate of infectious stones.

Although a considerable number of cases were included in this study, certain limitations should be noted in this study. First, the predominant source of stone specimens was surgical patients, which introduced a potential bias. Second, the scope of this study was confined to a single center; as a result, future research is warranted to encompass multiple centers. Moreover, the findings only represent the distribution characteristics of bladder stones in the Central China region. Lastly, the missing data somewhat compromised the precision of our results.

In summary, this study presented the analysis of bladder stone composition in East China, primarily in Jiangsu province. The results showed that CaOx was the most prevalent main component of bladder stones. Following calcium-containing stones, UA stones were the second most common type. Additionally, we found a strong correlation between the clinical characteristics and the types of stones. This study highlights the importance of gaining a deeper understanding of bladder stone composition, since it contributes to the more effective evaluation, treatment, and prevention of stone disease.

The authors would like to thank all our participants in this study.

Ethical approval and consent were not required as this study was based on publicly available data. This study did not require Institutional Review Board approval of Affiliated Hospital of Nanjing University of Chinese Medicine.

None of the authors have any conflicts of interest or financial relationships.

The authors did not receive support from any organization for the submitted work.

C.Z. and L.M. performed conception and design of the experiments, and writing of manuscript; Y.Z., X.C., Y.W., P.Z., and N.W. provided data collection, analysis, and interpretation of data; J.S., L.Y., and Y.X. prepared writing and revision of the article.

Chen Zhu, Long Ma, and Xuehua Chen contributed equally to this work.

The data that support the findings of this study are not publicly available due to their containing information that could compromise the privacy of research participants. Further inquiries can be directed to the corresponding author.