Estimates of Urinary Calcium Excretion in Dogs With and Without Calcium Oxalate Urolithiasis

ABSTRACT Background Fractional excretion of calcium (FeCa) and urine calcium‐to‐creatinine ratios (UCaCr) estimate hypercalciuria, but more data are needed on how well they discriminate between dogs with and without CaOx urolithiasis. Objective To determine the performance of FeCa and UCaCr in predicting CaOx urolith status. Animals One hundred twenty‐one client‐owned, normocalcemic dogs: 42 CaOx stone formers (cases) and 79 controls. Methods Analytical, retrospective, cross‐sectional study. FeCa (%) and UCaCr (mg/mg) were calculated using measurements from urine and blood and were compared by urolith status with Wilcoxon rank‐sum tests. Performance was determined with receiver operating characteristic curves; “optimal” thresholds were selected to maximize sensitivity and specificity. Potential predictors of FeCa and UCaCr (e.g., urolith status, sex, breed, age) were modeled with multivariable regression. Spearman's rank correlation was run for FeCa and UCaCr. Results FeCa and UCaCr were greater in cases than controls (p < 0.001 for both); medians were 0.81 (0.12–2.47) and 0.060 (0.008–0.176) in cases and 0.50 (0.08–2.61) and 0.032 (0.005–0.131) in controls. Optimal thresholds for FeCa (0.56) and UCaCr (0.056) had moderate sensitivity (74% and 60%, respectively) and specificity (58% and 75%, respectively). FeCa and UCaCr were strongly correlated (rho = 0.94, p < 0.001) and lower in males than in females (estimate = −0.70 and −0.64, p = 0.002 and 0.005, respectively). Conclusions and Clinical Importance FeCa or UCaCr perform moderately well for identifying CaOx cases; dogs with high values might benefit from therapy to reduce hypercalciuria. Their high correlation makes the determination of both unnecessary. Lower values in males support the development of sex‐specific thresholds.