ASSOCIATION OF METABOLIC SYNDROME AND ITS COMPONENT BURDEN WITH UPPER URINARY TRACT STONE COMPOSITION: A RETROSPECTIVE OBSERVATIONAL STUDY

Upper urinary tract stones are chemically heterogeneous, with compositions that reflect distinct underlying metabolic perturbations. Metabolic syndrome (MetS) comprises a cluster of interconnected metabolic abnormalities, but the relationship between the cumulative burden of these components and specific stone phenotypes remains incompletely characterized in Chinese populations. This study aimed to investigate the associations of MetS and the number of its components with upper urinary tract stone composition, with a particular focus on uric acid stones. This retrospective observational study included 800 patients with upper urinary tract stones and infrared spectroscopic stone-composition analysis at the Second Affiliated Hospital of Guilin Medical University. Patients were stratified by metabolic syndrome (MetS) status, and predominant stone composition was categorized as calcium oxalate, calcium phosphate, struvite, uric acid, or other. Overall composition differences were assessed by a chi-square test with Monte Carlo resampling. Logistic regression examined associations with uric acid stone composition after sequential adjustment for age, the female/male classification, and serum creatinine. Metabolic component burden was assessed using both categorical and linear terms; Firth penalized logistic regression was used in sensitivity analyses. Among 800 patients, 280 (35.0%) were classified as having MetS. Stone-composition distributions differed by MetS status (Monte Carlo P = 0.0058), and uric acid stones accounted for 13.2% of stones in the MetS group versus 5.6% in the non-MetS group. In the fully adjusted model, MetS was associated with greater odds of uric acid stone composition (OR = 2.65, 95% CI 1.57–4.50; P = 0.00028). Compared with the zero-component group, patients with two, three, and four components showed elevated odds of uric acid composition. The category-specific point estimate was highest in the three-component group (OR = 6.06, 95% CI 2.46–18.31); the categorical specification fitted better than the linear term (likelihood ratio P = 0.040). Firth estimates were directionally similar. Among patients with confirmed upper urinary tract stones, MetS was associated with increased odds of uric acid stone composition. A categorical analysis suggested that the association varied across metabolic component counts, although sparse events in some groups warrant cautious interpretation. These findings merit confirmation in independent patient cohorts with more complete metabolic profiling.