Linking Stone Mineral Composition to 24-Hour Urinary Metabolic Profiles: An Episode-Based Cohort Study

Stone composition reflects the urinary environment in which calculi form, whereas 24 h urine testing identifies modifiable lithogenic abnormalities. This study examined component-specific urinary metabolic profiles and evaluated whether routine clinical and urinary variables could distinguish common stone minerals.

This retrospective study included 256 patients undergoing 297 stone surgeries, consolidated into 256 treatment episodes. Fourier-transform infrared spectroscopy identified stone minerals, which were linked to preoperative 24 h urine profiles. Calcium oxalate monohydrate (COM), calcium oxalate dihydrate (COD), carbonate apatite, and anhydrous uric acid were evaluated using multivariable logistic regression. Mutually exclusive calcium oxalate-calcium phosphate phenotypes, nested cross-validated prediction models, and unsupervised clustering were also examined.

COM, COD, carbonate apatite, and anhydrous uric acid were present in 78.5%, 73.0%, 39.5%, and 9.8% of episodes, respectively. Higher urine pH was associated with carbonate apatite (odds ratio [OR] per standard deviation, 1.78; 95% confidence interval [CI], 1.33-2.38), whereas lower pH was associated with anhydrous uric acid (OR, 0.26; 95% CI, 0.11-0.58). Higher urinary citrate was associated with COM, but phenotype analysis showed that hypocitraturia increased from 45.3% in calcium oxalate-only episodes to 60.7% in mixed calcium oxalate-calcium phosphate episodes and 89.5% in calcium phosphate episodes without calcium oxalate. Lower urine volume was associated with COD. Cross-validated areas under the curve ranged from 0.654 to 0.712, and metabolic clusters showed substantial mineral overlap.

Urine pH provided the clearest component-specific signal, whereas citrate associations depended on accompanying minerals. Routine 24 h urine testing complemented but did not replace direct stone analysis.