Hypercalciuria is a common cause for stone formation in children. The aim was to delineate the role of urinary citrate in hypercalciuric children for protection against calcium stone formation. We evaluated random urine calcium, citrate, and creatinine in 149 controls, 78 hypercalciuric nonstone formers, and 34 hypercalciuric children with stone. Urine citrate/creatinine was highest in hypercalciuric nonstone formers 899 ± 351 compared with controls 711 ± 328 and stone formers 595 ± 289 (p < 0.01 vs. both). Calcium/creatinine ratio was similar in hypercalciuric stone and nonstone formers, but significantly higher than controls. Consequently, urine Calcium/citrate ratio (mg/mg) increased from control 0.17 ± 0.17 to 0.41 ± 0.23 (p < 0.001) in hypercalciuric nonstone formers, and to 0.65 ± 0.46 in stone formers (p < 0.001 compared with other groups). Area under receiver operating characteristic curve combined with multilevel risk analyses found calcium/citrate ratio of 0.326 to provide good discrimination between control and stone formers. We found 5th percentile for random urine citrate/creatinine ratio in school-aged children to be 176 mg/g, elevated urinary citrate excretion in hypercalciuric children to be protective against stone formation, and urine calcium/citrate ratio to be a good indicator for risk of stone formation. Whether intervention in hypercalciuric children to lower urine calcium/citrate <0.326 will provide protection against stone formation needs to be studied.
Abbreviations: ROC, receiver operating characteristic curve
UCa/Cit, urine calcium/citrate ratio
UCa/Cr, urine calcium/creatinine ratio
UCit/Cr, urine citrate/creatinine ratio