Does the Urinary Calcium/Citrate Ratio Add to the Diagnostic Workup of Children at Risk of Kidney Stones? A Cross-Sectional Study

Abstract

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.

Keywords

urinary calcium - urinary citrate - urinary creatinine - urinary oxalate - urolithiasis

Authors' Contributions

GF and ML articulated the conceptual framework for this study and obtained ethics approval. VB retrieved the urinary citrate concentrations from the laboratory information system and linked all available data. ML pulled all the charts and performed the data entry. GF developed the analytical approach and GF, ML, CIRC, and RN analyzed the data. GF and CIRC drafted the manuscript. RN, PW, and VB contributed to the interpretation of data, added intellectual content during manuscript preparation, and provided valuable feedback on various aspects of the manuscript. All authors read and approved the final manuscript.

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