Kidney stone formation is a multifactorial condition that involves interaction of environmental and genetic factors.1 In western countries, the prevalence and incidence of kidney stone formation have been reported to be 2% to 19%, with an increasing frequency among men.2 A previous study estimated that the overall prevalence of kidney stones in China was 4.0% (4.8% in men and 3.0% in women).3 The condition causes severe pain and is highly likely to be recurrent.4 In addition, the presence of kidney stones is strongly related to chronic kidney disease, bone loss and fractures, kidney cancer, coronary heart disease, hypertension, and metabolic syndrome.5 6 7 8 9 This results in a heavy economic and social burden.10 11 An appropriate prevention strategy is urgently needed to reduce the prevalence and health care costs that arise from the condition.

Currently, many domestic and international reports have focused on the risk factors for kidney stone formation. These diverse risk factors including age, gender, race, drugs, genetic, dietary, and environmental factors (eg occupation and heat exposure), insulin resistance, as well as drinking water are all reported to be associated with kidney stone prevalence.2 12 13 14 15 Clinical data on the prevalence and influencing factors in kidney stone disease in the north of China are scarce however, as is knowledge about the relationship between kidney stone formation and blood and urine parameters.

Our study aimed to explore the prevalence of kidney stone disease and the underlying causes in Shunyi District, Beijing, China. Shunyi District is an important district in the northeast of Beijing with a population of 953 000 in 2012. The results of this study may provide an insight into ways that can help prevent kidney stone formation.

All procedures were carried out in accordance with the ethical standards of the local institute and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This cross-sectional survey was conducted from December 2011 to November 2012. A total of 19 towns in the Shunyi District of Beijing were numbered randomly. A random number table was used to choose six towns from these 19 towns. The six towns included Zhangzhen, Mulin, Beiwu, Nanfaxin, Renhe, and Nancai. Residents who visited their township hospital for a routine physical examination were invited to participate in this survey.

The inclusion criteria of participants were the age of ≥18 years and as resident in the town for more than 3 years. The exclusion criteria were presence of kidney stones, renal failure, chronic gastric disease, urinary tract malformation, urinary tract obstructive disease, urinary tract infection, or hyperparathyroidism.

Verbal consent was obtained from all study participants following provision of information about the study objectives, procedures, and implications. The study was approved by the Ethics Committee of Beijing Shun-Yi Hospital.

All participants were asked to complete a questionnaire that covered the following: (1) demographic characteristics, including gender, age, body mass index, workplace, and job category. The amount of sweat following exercise was quantified and classified as dry, wet, and moist if the palm, forehead, axillary, and back were dry, wet, and dripping with sweat, respectively; (2) daily fluid intake, including water intake, source of drinking water, habits of drinking water; and fluid intake including tea, soup, and milk; (3) living and dietary habits, including outdoor activities, smoking, frequency of staple and non-staple food intake (sweetmeats, seafood, fruit, vegetables, bean products, dairy products, eggs, meat, and animal’s viscera); (4) personal and family history of urinary calculus, urinary tract infection, or hypertension; and (5) present diagnosis of kidney stone detected by a physician and its characteristics. To screen for the presence of kidney stones, all participants underwent an ultrasound examination that was performed by two attending physicians in each hospital.

To fully explore the potentially associated factors, 100 patients with kidney stone(s) were numbered and then randomly selected by computer for testing of blood and urine biochemical parameters. Specifically, levels of creatinine, calcium, phosphorus, potassium, and uric acid were measured in an early-morning urine and fasting blood samples using a biochemistry analyser, AU5400 (Beckman Coulter Ltd, United States). Blood concentration of chlorine and sodium was also measured. Simultaneously, 100 age- and sex-matched healthy participants who visited these hospitals for a routine physical examination during the study period and were confirmed to be free of urinary calculus or endocrine metabolic disease were selected as controls.

Data were entered into the computer using EpiData 3.1 (EpiData Association, Odense, Denmark) and analysed using the Statistical Package for the Social Sciences (Windows version 19.0; IBM Corp, Armonk [NY], United States). Continuous variables are presented as mean ± standard deviation, and categorical variables as percentages. Univariate analysis of continuous and categorical variables was first performed by Spearman’s correlation coefficient (r_s) and Pearson Chi squared (χ²) value, respectively. Statistically significant variables were further analysed by multivariate stepwise logistic regression to explore the potential influencing factors. The inclusion criteria was 0.05, and the exclusion criteria was 0.1. Odds ratios (ORs) with corresponding 95% confidence intervals (CIs) were calculated. A P value of <0.05 was considered statistically significant.

A convenient sample of 3361 subjects was invited to participate in this study, of whom 3350 completed the survey with 1091 males and 2259 females. The response rate was 99.67%. The mean age of all participants was 48.97 ± 17.02 years (range, 20-98 years), with 54.46 ± 13.23 years for males and 51.81 ± 11.24 years for females.

Presence of kidney stones was newly diagnosed in 121 subjects (3.61%; 95% CI, 2.88%-4.32%) including 67 (6.14%) males and 54 (2.39%) females. As shown in Table 1, univariate analysis showed that 31 variables were significantly associated with the presence of kidney stones—including gender; age; place of work; occupation; amount of exercise, sweat, daily water intake; water source; intake of fluid, alcohol, coffee, tea, soup, white spirits, and milk; outdoor activity; smoking; eating eggs and meat; presence of kidney stones in relatives, parents, and siblings; as well as personal history of hypertension, urinary stone, urinary tract infections, chronic gastric diseases, hyperlipidaemia, diabetes, kidney surgery, ureter surgery; and prescription of a diuretic.

Biochemical parameters were measured in blood and urine samples. As shown in Table 2, the concentration of serum creatinine, calcium, and uric acid in blood differed significantly in patients with and without kidney stone(s), suggesting that the three variables were potentially associated with this disease. No statistical difference was observed in the concentration of other variables. With regard to the level of these parameters in urine, no significant difference was found between the patients with kidney stone and the healthy controls (Table 2).

Multivariate logistic regression analysis was performed to control for the effects of confounding factors and analyse the factors potentially associated with kidney stone formation (Table 3). Three variables were finally entered into the multiple logistic regression model: male gender (OR=102.681; 95% CI, 1.062-9925.797; P=0.047), daily intake of white spirits (OR=6.331; 95% CI, 1.204-33.282; P=0.029), and personal history of urolithiasis (OR=1797.775; 95% CI, 24.228-133 396.982; P=0.001).

In this population-based cross-sectional study, the prevalence of kidney stones and the underlying associated factors were investigated in the Shunyi District of Beijing, China. A total of 1091 males and 2259 females were enrolled in the study. The prevalence of kidney stone was 3.61% among the participants. The results demonstrated that male gender, daily drinking of white spirits, and a personal history of urolithiasis were potential risk factors for kidney stone formation. Our results may help gain better insight into the prevention of kidney stones.

Previous studies reported that the prevalence of kidney stone varies with geographical location and socio-economic conditions, and is stratified by age.16 Global epidemiological surveys demonstrated that the mean prevalence of kidney stone was 3.25% in the 1980s and 5.64% in the 1990s.17 18 Specifically, kidney stone affects approximately one in 20 people in Spain and 1 in 25 in China, while the prevalence reaches up to 9.1% in the United States and 16.9% in Northeast Thailand.3 19 20 21 In the present study, the prevalence was determined to be 3.61% in the six randomly selected towns of Shunyi District, and is consistent with the findings of the first national survey of kidney stone in China (4.0%).3 Unfortunately, we collected 3361 subjects without collecting information about how they were distributed in the six towns. Although these towns were randomly selected from a total of 19 towns, self-selection bias was likely present in the current study, as the study samples were taken by convenient sampling from volunteers who attended any one of the six hospitals for physical examination for a non-specified reason. Thus, further studies with a more representative population are needed to verify whether the prevalence in the Shunyi District of Beijing is in line with that in the six randomly selected towns.

In the present study, prevalence of kidney stones was also found to be higher in men (6.14%) than in women (2.39%). Male gender was identified as a risk factor in multivariate logistic regression analysis. The reasons might be complicated. A hormonal factor may be one of the key reasons for the difference between men and women. For instance, the secretion of citric acid in urine, as a protective factor against kidney stone formation, is promoted by oestrogen. Androgen leads to the accumulation of some damaging factors for kidney stone formation, such as calcium, oxalate, and uric acid in urine.22 23 Men are also more likely to engage in heavy physical labour, to sweat more, and more often be dehydrated. These factors are documented risk factors for kidney stone formation.24 25 Nonetheless they were not successfully retained in the stepwise regression in our study, implying that they did not have an independent effect on the outcome in our study sample, possibly due to the small sample size. Further studies with a larger sample size are needed to verify our findings.

A recent meta-analysis found that alcohol intake is inversely associated with the risk of urolithiasis.26 On the contrary, our results showed that daily drinking of white spirits was a risk factor for kidney stone formation. The differences might be attributed to the varied drinking habits of different races and countries. Curhan et al12 established that a family history of kidney stones substantially increased the risk of stone formation. Moreover, increasing studies have found that patients who have ever had urolithiasis have a higher prevalence of kidney stone formation than those without such a history.27 28 In concordance with these findings, our study revealed that a history of urolithiasis was a potential risk factor for kidney stone formation. Therefore, people who favour liquor and/or have a history of urinary tract stones should be aware of their higher risk for kidney stone formation and take preventive steps.

This study has several limitations and the results must be interpreted with caution. First, the study sample might not be representative of the population because of the convenient sampling of volunteers. Also, the number of subjects excluded under each of the exclusion criteria was not recorded. Second, the small sample size hindered the proper control of potential confounding factors. Third, the causal relationship between the involved factors and kidney stone formation could not be confirmed by a cross-sectional survey. Fourth, recall bias and volunteer bias could not be avoided. Finally, females were over-represented in the sample as many males were migrant workers and often worked in other cities. More rigorous studies with a larger and more representative population are needed to verify the results.

The prevalence of kidney stones in the current study sample of the selected towns (Zhangzhen, Mulin, Beiwu, Nanfaxin, Renhe, and Nancai) of Shunyi District of Beijing, China, is 3.61%. Male gender, daily drinking of white spirits, and a history of urolithiasis are factors potentially associated with kidney stone formation.

This study was supported by Capital Medical Development Research Fund (2009-2107). The authors declare that they have no competing interests.

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