Abstract
The current report aimed to evaluate the characteristics of stone composition in 3637 renal and ureteral calculi patients in a single center while clarifying its relationship with sex, age, and time. Out of 3637 cases of upper urinary tract stones, stone specimens were analyzed retrospectively. There were 2373 male patients aged 6 months-87 years, with an average age of 44.73 ± 15.63 years, and 1264 female patients aged 4 months-87 years, with an average age of 46.84 ± 16.00 years. The male-female ratio was 1.88:1. Five hundred twelve patients had ureteral calculi, and 3125 had renal calculi. The SPSS software helped analyze the relationship between renal and ureteral calculi composition and sex, age, and time. Stone composition demonstrated 2205 cases of calcium oxalate stones (60.6%), 518 carbonate apatite (14.2%), 386 uric acids (10.6%), 232 magnesium ammonium phosphate (6.4%), 117 calcium phosphate (3.2%), 76 cystine (2.1%), 47 sodium urate (1.3%), 31 others (0.9%), and 25 ammonium urate (0.7%) cases. The overall male-to-female sex ratio was 1.88:1. Stones in the upper urinary tract were significantly more frequent in men than in women between the ages of 31 and 60. However, such stones were significantly more frequent in women than men over 80 (P < .05). Cystine, Sodium urate, Carbonated apatite, and uric acid indicated significant differences between different age categories (all P < .001). Stone composition analyses revealed that the frequency of calcium oxalate calculi has increased annually, while cystine and carbonated apatite incidences have dropped annually over the past decade. The components of renal and ureteral calculi vary significantly based on age and sex, with calcium oxalate calculi being more frequent in men while magnesium ammonium phosphate stones are more frequent in female patients. The age between 31 and 60 years is the most prevalent for renal and ureteral calculi in men and women.
Keywords: age, calcium oxalate stones, gender, renal calculi, stone composition analysis
1. Introduction
Urolithiasis is a common urinary tract disease with several etiologic factors and is a public health burden worldwide. Studies have revealed that geographic and gender differences characterize its incidence. In addition, urolithiasis is characterized by high morbidity and recurrence rates. According to the stone formation mechanism, stones can be categorized as infectious or metabolic. Identifying stone components can benefit patients by depicting potential metabolic risk factors while helping physicians determine appropriate stone treatment and prevention strategies. The current study aimed to analyze the stone composition characteristics in 3637 cases with upper urinary tract stones from a single center in northern China while clarifying the relationship with gender, age, and time.
2. Methods
Overall, 3637 patients were enrolled whose samples were obtained from June 2009 to June 2018 from renal and ureteral calculi patients in Peking University People Hospital. The samples were obtained using drug lithotripsy, extracorporeal shock wave lithotripsy, ureteroscopic lithotripsy, and percutaneous nephrolithotomy. The ethics committee of Peking University People Hospital approved the study, and all participants provided informed consent. There were 2373 male patients aged 6 months-87 years, with a mean age of 44.73 ± 15.63 years, and 1264 female patients. The average age was 46.84 ± 16.00 years (4 months to 87 years). The male-female ratio was 1.88:1, with 512 Five hundred twelve patients having ureteral calculi and 3125 having renal calculi.
The stones were washed and dried at 75°C. Stone powder (1 mg) was mixed using dry potassium bromide (200 mg), and the mixture was ground using an agate mortar. The mixture was pressed into a translucent sheet and scanned inside an automated infrared spectral analysis system (Lambda, Tianjin, China). Finally, a computer helped plot the spectra and analyze the composition of the stones, followed by recording the significant serum components. Based on the European Association of Urology, the stone components are calcium oxalate, calcium phosphate, uric acid, magnesium ammonium phosphate, apatite carbonate, ammonium urate, and cystine. Infected stones can be differentially diagnosed through various criteria. The most used diagnostic criteria of the European Association of Urology Guidelines for the Diagnosis and Treatment of Urological Stones[1] incorporate stones with one or more of the following components: magnesium-ammonium phosphate, carbonate-apatite, and ammonium urate. The stone composition analysis of 31 patients was rarely categorized as other types, including calcite in 21 cases, 2,8-dihydroxyadenine in 4 instances, xanthine in 3, quartz in 2 minutes, and silica in 1. We recorded sodium urate.
2.1. Analyze statistics
Categorical variables are characterized as percentages. Measurement data are displayed as mean ± SD. The chi-squared test helped evaluate the influence of age and sex on different stone categories. Fisher exact test was applied if the chi-squared test was not suitable. The significance level was set at P < .05, and statistical analyses were performed using SPSS 19.
3. Results
The stone composition analysis indicated 2205 cases of calcium oxalate stones (60.6%), 518 carbonate apatite (14.2%), 386 uric acid (10.6%), 232 magnesium ammonium phosphate (6.4%), 117 calcium phosphate (3.2%), 76 cystine (2.1%), 47 sodium urate (1.3%), 31 others (0.9%), and 25 ammonium urate (0.7%) cases. The overall male-to-female sex ratio was 1.88:1 in this study. Stones in the upper urinary tract were significantly more frequent in men between the ages of 31 and 60 than in women. However, the stones were substantially more frequent in women than in men over the age of 80 (P < .05) (Table 1). The components of stones in the groups of different sexes are represented in Table 2. The percentage of calcium oxalate stones was higher in male patients than in females (65.8% vs 50.9%, χ2 = 77.255, P < .001). Moreover, the percentage of infected stones was higher in female patients than in males (33.7% vs 14.7%, χ2 = 177.466, P < .001). The proportion of uric acid stones was much higher in male patients than in females (12.2% vs 7.6%, χ2 = 18.603, P < .001). Moreover, the proportion of sodium urate stones was much higher in female patients than in males (1.8% vs 1.0%, χ2 = 4.224, P = .040).
Table 1.
Relationship between age and gender of upper urinary tract stones.
| Age (yr) | Male (n,%) | Female (n,%) | Male to female ratio | χ2 | P |
|---|---|---|---|---|---|
| <10 | 104 (4.4) | 43 (3.4) | 2.42:1 | 2.045 | .153 |
| 11–20 | 30 (1.3) | 14 (1.1) | 2.14:1 | 0.169 | .681 |
| 21–30 | 254 (10.7) | 144 (11.4) | 1.76:1 | 0.401 | .526 |
| 31–40 | 490 (20.6) | 221 (17.5) | 2.22:1 | 5.252 | .022 |
| 41–50 | 594 (25.0) | 267 (21.1) | 2.22:1 | 6.971 | .008 |
| 51–60 | 558 (23.5) | 341 (27.0) | 1.64:1 | 5.316 | .021 |
| 61–70 | 263 (11.1) | 165 (13.1) | 1.59:1 | 3.085 | .079 |
| 71–80 | 68 (2.9) | 55 (4.4) | 1.24:1 | 5.571 | .018 |
| 81–90 | 12 (0.5) | 14 (1.1) | 0.86:1 | 4.310 | .040 |
| 2373 | 1264 |
P value for comparison between age and gender.
Table 2.
Relationship between gender and stone composition in patients with upper urinary tract stones.
| Stone composition | Male(n, %) | Female(n, %) | χ2 | P |
|---|---|---|---|---|
| Calcium oxalate | 1562 (65.8) | 643 (50.9) | 77.255 | <.001 |
| Carbonated apatite | 260 (11.0) | 258 (20.4) | 60.360 | <.001 |
| Uric acid | 290 (12.2) | 96 (7.6) | 18.603 | <.001 |
| Magnesium ammonium phosphate | 72 (3.0) | 160 (12.7) | 127.909 | <.001 |
| Calcium phosphate | 76 (3.2) | 41 (3.2) | 0.004 | .947 |
| Cystine | 47 (2.0) | 29 (2.3) | 0.397 | .529 |
| Sodium urate | 24 (1.0) | 23 (1.8) | 4.224 | .040 |
| Other | 25 (1.1) | 6 (0.5) | 3.270 | .071 |
| Ammonium urate | 17 (0.7) | 8 (0.6) | 0.084 | .772 |
| Infectious stones | 349 (14.7) | 426 (33.7) | 177.466 | <.001 |
| 2373 | 1264 |
P value for comparison between gender and stone composition.
The data from the current study revealed that 21–70 years was the preferred age for renal and ureteral calculi in male (90.9%) and female (90.0%) patients. The highest stone percentage occurred in male patients (48.5%) between 41 and 60 years of age. Moreover, the highest stone percentage occurred in female patients (48.1%) between 41 and 60 years of age. Cystine, sodium urate, carbonate apatite, and uric acid indicated significant differences across age groups (all P < .001) (Table 3).
Table 3.
Relationship between age group and composition of upper urinary tract stones in patients.
| Stone composition | 0–20 (n,%) |
21–40 (n,%) |
41–60 (n,%) |
61–87 (n,%) |
χ2 | P |
|---|---|---|---|---|---|---|
| Calcium oxalate | 101 (52.9) | 648 (58.4) | 1103 (62.7) | 353 (61.2) | 10.195 | .017 |
| Cystine | 25 (13.1) | 26 (2.3) | 20 (1.1) | 5 (0.9) | 67.266 | <.001 |
| Calcium phosphate | 7 (3.7) | 47 (4.2) | 43 (2.4) | 20 (3.5) | 7.337 | .062 |
| Uric acid | 11 (5.8) | 72 (6.5) | 213 (12.1) | 90 (15.6) | 43.821 | <.001 |
| Sodium urate | 5 (2.6) | 13 (1.2) | 21 (1.2) | 8 (1.4) | 2.338 | .505 |
| Ammonium urate | 14 (7.3) | 5 (0.5) | 4 (0.2) | 2 (0.3) | 51.380 | <.001 |
| Magnesium ammonium phosphate | 5 (2.6) | 74 (6.7) | 117 (6.6) | 36 (6.2) | 4.916 | .178 |
| Carbonated apatite | 17 (8.9) | 221 (19.9) | 225 (12.8) | 55 (9.5) | 47.358 | <.001 |
| Others | 6 (3.1) | 3 (0.3) | 14 (8.0) | 8 (1.4) | 44.618 | <.001 |
| 191 | 1109 | 1760 | 577 |
P value for comparison between age group and stone composition.
Stone composition analysis revealed that the prevalence of calcium oxalate calculi has increased annually over the past decade. However, cystine and carbonated apatite incidences have decreased annually in the past decade (Fig. 1).
Figure 1.
Trends in stone composition over the period 2009 to 2018.
4. Discussion
Urolithiasis is a common urinary tract disease. The incidence of kidney calculi in adults increased significantly nationally and internationally.[2] Nearly 13% of adults will develop a kidney stone during their lifetime.[3] Studies have described a recurrence rate of almost 40% within 5 years, 50% in 10 years, and 75% in 20 years post-treatment.[4] The formation process of urinary stones is complex, with various stone components. Hence, stone composition analysis is necessary to clarify the etiology of the patient stones and prevent stone recurrence.
Stone composition analysis methods primarily include chemical analysis, infrared spectroscopy, polarized light microscopy, and X-ray diffraction analysis. Infrared spectroscopy is based on stone samples in the infrared region of the absorption peak characteristics to decipher the structure and composition of stones. It can be qualitative and semi-quantitative analyses, as studying the composition of stones is a more ideal analytical method.[5]
Epidemiologic research has demonstrated that the prevalence of urinary tract stones is more common in men than in women. The male-female ratio was 1.88:1 in this study, consistent with previous studies.[5,6] The higher prevalence of upper urinary tract calculi in men could be related to anatomical structure, dietary habits, sex hormone levels, and other factors.[7,8] Urinary stones can be divided into metabolic and infectious stones. Previous studies have depicted that men are predisposed to developing metabolic stones. Simultaneously, women are prone to developing infectious stones because of urinary tract infections (UTI).[9]
Calcium oxalate calculi are the predominant type of upper urinary tract stones. Previous studies have indicated that dietary intake of oxalate and calcium can significantly impact oxaluria excretion and calcium oxalate calculi formation.[10,11] Increased dietary oxalate intake leads to increased urinary oxalate excretion, while decreased intake induces reduced urinary oxalate excretion. Dietary calcium intake has a dual impact on urinary oxalate excretion. However, previous researchers have demonstrated that calcium oxalate calculi recur more in the low-calcium diet group than in those on a regular diet.[12] The calcium oxalate calculi percentage was 60.6%, the highest in men and women, gradually increasing in the last 10 years.
Previous studies have described that the incidence of uric acid stones is about 10% of all urinary tract stones.[13] However, this percentage becomes extremely high among gout patients.[14] The percentage of uric acid calculi patients in our study was 10.6%, consistent with the previous report. Our findings depict that uric acid stones increase with age, particularly for ages over 40 years. Uric acid calculi formation is a complex disease linked to obesity, insulin resistance, and diabetes mellitus.[15–17] Moreover, the persistence of acidic urine (pH ≤ 5.5) is the leading risk factor for uric acid calculi formation, along with climate and diet. Dry and hot climates enhance fluid loss, decreasing urination with lower urine pH.[18,19]
UTIs are a significant risk factor for upper urinary tract stones, where bacteria can behave as a heterogeneous core of stone matrix components and enhance stone formation. This induces calcium phosphate precipitation and contributes to crystal nucleation, growth, and aggregation, forming stones.[20] Infected stone pathogenesis involves the hydrolysis of water and urea using urease to synthesize CO2 and ammonia, increasing the urine pH from 7.2 to 8.0. Ammonia is hydrolyzed with water to develop ammonium, while CO2 reacts with water to build bicarbonate. Phosphate solubility decreases at urine pH > 7.2, forming magnesium ammonium phosphate stones with magnesium ions and phosphate anions. Apatite carbonate forms with calcium ions and phosphate anions at pH 6.8 to 7.2, forming magnesium ammonium phosphate stones and apatite carbonate stones with rapidly growing bacteria. The anatomical characteristics of the female urethra pose a greater susceptibility to UTIs than in men.[21] Moreover, postmenopausal women are more susceptible to complex UTIs because of reduced estrogen levels. This causes a change in vaginal pH while increasing Escherichia coli colonization. In this study, the percentage of infected stones was higher among women than men (33.7% vs 14.7%, P < .001), particularly for magnesium ammonium phosphate and carbonated apatite, consistent with previous studies.[8,20]
Although the sample size of this study is relatively large, there are some limitations. Firstly, it was retrospective single-center research that might not represent actual incidences. The number and quality of our studies will be increased in the future. Secondly, most stones were obtained from patients undergoing extracorporeal shock wave lithotripsy, ureteroscopic lithotripsy, percutaneous nephrolithotomy, and medical therapy. This could have introduced a bias toward stones requiring specific interventions. Finally, data on patient characteristics other than year, sex, and age were unavailable.
5. Conclusions
Upper urinary tract stones were significantly more common in men aged 31 to 60 than women. However, it is more common in women than men over 80 (P < .05). Cystine, sodium urate, carbonated apatite, and uric acid depicted significant differences among age categories (all P < .001). Stone composition analysis indicated that the prevalence of calcium oxalate calculi has increased annually over the past decade. Moreover, cystine and carbonated apatite incidences have decreased annually over the past 10 years.
Author contributions
Conceptualization: Qingquan Xu.
Formal analysis: Lizhe An, Liulin Xiong.
Investigation: Luping Yu.
Methodology: Xiaobo Huang.
Writing – original draft: Yang Hong.
Writing – review & editing: Tao Xu.
Abbreviation:
- UTI
- urinary tract infection
YH and LY contributed equally to this work.
The authors have no funding and conflicts of interest to disclose.
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
How to cite this article: Hong Y, Yu L, Huang X, An L, Xiong L, Xu Q, Xu T. Composition analysis of renal and ureteral calculi in a single center in northern China in the past decade. Medicine 2024;103:10(e37374).
Contributor Information
Yang Hong, Email: 1446347933@qq.com.
Luping Yu, Email: ylp0827@hotmail.com.
Xiaobo Huang, Email: huang6299@sina.com.
Lizhe An, Email: qdalz@126.com.
Liulin Xiong, Email: xiongliulin@sina.com.
Tao Xu, Email: xutao@pkuph.edu.cn.
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