Clinical and Metabolic Correlates of Calcium Oxalate Stone Subtypes: Implications for Etiology and Management

Introduction: Calcium oxalate (CaOx) is the predominate component within renal calculi and can be divided into two subtypes: CaOx-monohydrate (COM) and CaOx-dihydrate (COD). COM and COD form in differing urinary environments, which suggest differential underlying metabolic abnormalities associated with each subtype. We compared clinical and metabolic findings in CaOx stone formers to delineate factors differentiating COD and COM stone formers and the implication this holds in terms of etiology and treatment. Patients and Methods: We identified CaOx stone formers that had passed their stones or had undergone endoscopic extraction between October 2014 and December 2018. Only patients who had a predominant subtype (>= 80% COM or COD) and who had a 24-hour urine evaluation before medical management were included. Clinical and metabolic factors were compared in the two subgroups. Results: Out of 157 stone formers, 121 were COM and 36 were COD. COD formers were younger than COM formers with a mean age of 53 +/- 16 vs 59 +/- 15, respectively (p = 0.038). There were no observable differences in gender, body mass index, hypertension, diabetes mellitus, or hyperlipidemia. COM formers exhibited higher rates of hypocitraturia and hyperoxaluria, p = 0.022 and p = 0.018, respectively. Conversely, COD formers had significantly higher rates of hypercalciuria (47% vs 28%, p = 0.012). Multivariate analysis found hypercalciuria to independently predict COD (p = 0.043) and hyperoxaluria to predict COM stones (p = 0.016). Conclusion: COM formers are more likely to have hyperoxaluria, hypocitraturia, and elevated urinary oxalate levels compared to COD formers. COD formers exhibited higher incidence of hypercalciuria. These data suggest that all CaOx stones are not alike and that distinct metabolic and clinical etiological differences exist that may guide future management and prevention.