The purpose of the study was to evaluate urinary citrate/creatinine (U Ci /U Cr ) and urinary calcium/citrate (U Ca /U Ci ) ratios for distinguishing stone formers (SF) from non-stone formers (NSF) in an at-risk population. This was a retrospective study that included all pediatric patients who underwent urinary citrate testing from April 2017 to March 2018. The urinary levels of citrate, calcium, sodium, potassium, creatinine, oxalate, urate, pH, and specific gravity (SG) were measured in our clinical laboratory. Diagnosis of kidney stones was obtained through chart review. A total of 97 patients were included (46 NSF and 51 SF). The U Ci /U Cr ratio was not significantly different between NSF and SF. Median U Ca /U Cr ratio was higher in SF (0.67) compared with NSF (0.21, p < 0.0001). The median ratio of U Ca /U Ci was also higher in SF (1.30) than in NSF (0.65, p = 0.001). Oxalate, urate, pH, SG, and urinary sodium/potassium ratio did not differentiate between the SF and NSF. Positive correlation was seen between U Ca /U Cr and urinary sodium/creatinine U Na /U Cr (p < 0.0001), as well as between U Ca /U Cr and U Ci /U Cr (p < 0.0001). The study has demonstrated significantly higher U Ca /U Ci and U Ca /U Cr in SF compared with NSF, while the use of urinary oxalate, urate, pH, and SG did not differentiate between SF from NSF. We also confirmed a positive correlation between U Na /U Cr and U Ca /U Cr . While the utility of U Ca /U Cr is well established, our data suggest that U Ca /U Ci rather than U Ci /U Cr may be more predictive in the clinical setting when evaluating for nephrolithiasis.
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