Background: Excessive urine calcium excretion (hypercalciuria) impacts management of calcium oxalate (CaOx) urolithiasis in dogs. Fractional excretion of calcium (FeCa) and urine calcium-to-creatinine ratios (UCaCr) estimate hypercalciuria, but more data is needed on how well they discriminate between dogs with and without CaOx urolithiasis. Hypothesis/
Objective: To determine the performance of FeCa and UCaCr in predicting CaOx status. Animals: 121 client-owned, normocalcemic dogs (42 CaOx cases, 79 controls).
Methods: Analytical, cross-sectional study. Fasting urine calcium and creatinine and blood ionized calcium and creatinine concentrations were obtained. FeCa and UCaCr were calculated and compared by CaOx status with Wilcoxon rank-sum tests. Performance was determined at multiple thresholds, and receiver operating characteristic curves were generated. Potential predictors of log-transformed FeCa and UCaCr (e.g., sex, breed, age, blood ionized calcium concentration) were evaluated with multivariable regression. Spearman’s rank correlation was run for FeCa and UCaCr.
Results: FeCa and UCaCr were greater in CaOx cases (median = 0.81% and 0.060, respectively) than controls (median = 0.50% and 0.032, respectively; P<.001 for both). Table 1 shows performance at multiple thresholds. FeCa and UCaCr were highly correlated. (rho = 0.94, P<.001), and both were lower in males (estimate = -0.70 and -0.64, P=.002 and .005 respectively). Conclusions and clinical importance: FeCa or UCaCr perform moderately well for identifying CaOx cases; those with high values might benefit from therapy to reduce hypercalciuria. Given their high correlation, determination of both appears unnecessary. Lower values in males support the need for sex-specific thresholds.
