Urolithiasis has been reported as a male-dominant disease. Lin et al.  using the 2010 National Health Insurance report in Taiwan reported the urolithiasis (ICD9 codes 592 and 594) maletofemale ratio in emergency visits is higher than the ratio in nonemergency visits (2.61 in emergency vs. 1.75 in in and outpatient clinics). We previously showed a 2.93 ratio a decade ago , whereas in this study, we reported a 2.67 ratio, indicating an increasing prevalence of stone disease among women. The gender gap in urolithiasis prevalence appears to be closing in the past decade. Several possible reasons can explain the trend of stone disease among women. Previous NHANES data show that obesity and metabolic syndrome rates significantly increased among American women . Obesity also increases the risk of diabetes, hypertension, and dyslipidemia. Theses comorbidities had been considered to be related to stone formation . Adults with high BMI not only elicit specific changes in systemic effects of the body but also influence specific organs, which may ultimately increase the stone formation . A current study  in Taiwan showed the prevalence trend of overweight and obesity (BMI ≥ 24 kg/m2) has increased and remained stable. However, the prevalence trend of obesity (BMI ≥ 27 kg/m2) was continuously increasing. Moreover, a noticeable increase in the morbid obesity (BMI ≥ 35 kg/m2) prevalence was observed during the same period, from 0.4–1.4%. However, the prevalence of overweight decreased from 25.5–21.3%. These findings suggest that although the prevalence stabilized for overweight and obesity as a whole, the prevalence of obesity including the “morbid obesity” is dramatically increasing. Another important reason is the prevalence of diabetes has been increasing with female preponderance over the past decades in Taiwan . This may also explain the decreasing male-to-female ratio. In our study cohort, we also noted the prevalence of diabetes is higher in the female population. Previous studies [5–7, 21, 22] also focused on the relationship between sex hormones and physiologic changes affecting stone formation. Postmenopausal status, either natural or surgical menopause, is associated with higher risk of kidney stone incidence . Estrogen treatment is reported to decrease the risk of stone recurrence in postmenopausal women by decreasing urinary calcium and calcium oxalate saturation . The mean age at menopause was 50.2 years in Taiwanese women . We find that women in this series predominantly aged > 50 years compared to men (67.3% and 45.9%, p < 0.001, respectively). They may currently under the postmenopausal stage. This matching menopausal status for women may also explain the increase of female stone diseases rate.
Urolithiasis has been associated with several serious outcomes including development of renal function deterioration and even end-stage renal disease [3, 10–13]. One meta-analysis showed that a history of kidney urolithiasis was associated with an increased adjusted risk estimate for CKD (risk ratio, 1.47; 95% CI [1.23–1.76]) based on analyzing seven studies . A large study with a mean follow-up of 12 years showed recurrent symptomatic kidney stone formers were at higher risk for ESRD compared with non-stone formers both before and after adjustment for other comorbid conditions . They concluded that the stone events are associated with kidney injury. A recent study  assessed whether urinary oxalate excretion is a risk factor for more rapid CKD progression toward kidney failure. They found higher oxalate excretion was independently associated with greater risks of both CKD progression and ESRD, and results were similar when treating death as a competing event. Higher urinary oxalate level is known to be associated not only with nephrocalcinosis and kidney oxalate stones but also progressive renal function deterioration in patients with enteric hyperoxaluria and primary hyperoxaluria . Our previous report  showed patients with uric acid stones had higher age (P < 0.001), much lower urine pH (P < 0.001), and higher serum uric acid level (P = 0.002). Remarkably, those with uric acid stones had worse GFR than those with nonuric acid stones. We concluded that uric acid stones are associated with higher prevalence of CKD and especially in female patients with uric acid stones.
The prevalence of infection stone, composed of struvite and/or apatite, among women in our study was 1.7 times of that in men (30.6% vs. 18.1%, p < 0.001). Women are prone to suffer from urinary tract infection, which will lead to the elevation of urinary pH level and promote growth of urease-producing organisms . In our institute, PCNL was more frequently performed in the female population, which oftentimes suffered from more complex stones than that in the male population. In other words, female patients who underwent PCNL are thought to have more severe renal stones than those who did not. In addition, due to anatomical differences, men are more likely to suffer from benign prostatic hyperplasia and intravesical prostatic protrusion, which may subsequently obstruct the urethra, resulting in bladder stone formation . Our result also showed that cystolithotripsy was more frequently in men.