Clinical and Metabolic Factors Affecting the Proportion of Calcium Oxalate Monohydrate and Dihydrate in Pure Calcium Oxalate Stone Formers

Abstract

Abstract Objective: To investigate the association of different clinical and metabolic factors on the presence of calcium oxalate (CaOx) subtypes - CaOx monohydrate (COM) and dihydrate (COD) - in pure CaOx stone formers. Material and Methods: We assessed patients with pure CaOx nephrolithiasis found after endourological stone removal at a single center between January 2017 and December 2019. Inclusion criteria comprised patients who had a 24-hour urinary stone risk profile within three months of their stone analysis and before initiating any medical management. Two correlational analyses were performed: linear regression to predict the COD percentage in the specimen, and logistic regression to predict the presence or absence of ≥ 20% COD. Predictor variables included age, body mass index (BMI), gender, race/ethnicity, chronic medical conditions, and 24-hour urinary metabolic abnormalities. Results: Of 120 patients with CaOx stones, 38 (31.7%) contained ≥ 20% COD. We found significant associations between percentage of COD and several variables, including age (p=0.015), BMI (p=0.034), 24-hour urinary pH (p=0.001), as well as supersaturation of CaOx (p=0.019), brushite (p<0.001), and uric acid (p=0.011). Additionally, we found a significant association between younger patients (p=0.012), BMI (p=0.039), urine pH (p=0.027), potassium in urine (p=0.015), CaOx supersaturation (p=0.046), and brushite supersaturation (p=0.001) with the presence of significant percentage (≥ 20%) of COD. Conclusion: Patients with elevated proportion of COD are often younger and have a lower BMI. Additionally, as urinary pH becomes more alkaline, or the supersaturations of CaOx or brushite increase the relative proportion of dihydrate increases.