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Introduction

Recent epidemiologic studies have shown an increased prevalence of kidney stones in patients with metabolic syndrome (MetS). We have reported that the clustering of MetS traits is associated with greater severity of kidney stone disease (Am J Kidney Dis 61: 923-929, 2013). The aim of the present study is to clarify which stone composition is associated with MetS.

Methods

We retrospectively analyzed detailed clinical data from 30,448 patients with urolithiasis enrolled in the 6th Nationwide Survey on Urolithiasis in Japan conducted in 2005. Patients with lower urinary tract stones, struvite stones, cystine stones, other types of rare stone composition, unknown stone composition, or hyperparathyroidism and those younger than 15 years were excluded. According to the types of stone composition, the severity of kidney stone disease, assessed by the number of existing stones (single/multiple) and number of stone episodes (first time/recurrent), and abnormalities in urine constituents were examined by the number of MetS traits (obesity, hypertension, dyslipidemia, and diabetes).

Results

A total of 4,440 patients included in the final analyses were classified into four groups: calcium oxalate (CaOx) (n=3213), CaOx + calcium phosphate (CaP) (n=881), CaP (n=115), uric acid (UA) (n=191). The proportions of patients with recurrent and/or multiple stones significantly increased with the number of MetS traits only in patients with CaOx stone (P < 0.01, table 1). However, similar associations were not observed in patients with other stone compositions. In patients with CaOx stone, there was a significant and stepwise increase in the odds of recurrent and/or multiple stones after adjustment for age and sex. In patients with 3 or 4 MetS traits, the odds was 1.8-fold greater compared with patients with 0 traits (OR, 1.78; 95% CI, 1.29-2.42). In addition, the presence of MetS traits was associated with significantly increased odds of having hypercalciuria in patients with CaOx stone after adjustment for age and sex.

Conclusions

In patients with CaOx stone, MetS trait clustering is associated with greater severity of the disease and increased urinary calcium excretion. These results suggest that CaOx stone disease should be regarded as a systemic disorder linked to MetS.

Funding

none