Abstract
The purpose of the study was to evaluate urinary citrate/creatinine (UCi/UCr) and urinary calcium/citrate (UCa/UCi) 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 UCi/UCr ratio was not significantly different between NSF and SF. Median UCa/UCr ratio was higher in SF (0.67) compared with NSF (0.21, p < 0.0001). The median ratio of UCa/UCi 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 UCa/UCr and urinary sodium/creatinine UNa/UCr (p < 0.0001), as well as between UCa/UCr and UCi/UCr (p < 0.0001).The study has demonstrated significantly higher UCa/UCi and UCa/UCr 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 UNa/UCr and UCa/UCr. While the utility of UCa/UCr is well established, our data suggest that UCa/UCi rather than UCi/UCr may be more predictive in the clinical setting when evaluating for nephrolithiasis.
Highlights
The prevalence of urolithiasis is increasing around the world, especially among children.[1]
Many factors contribute to nephro- or urolithiasis, the current recommended approach is the use of UCa/UCr and UCi/UCr for distinguishing stone formers (SF) from NSF
The present study suggests that elevated urinary calcium/citrate (UCa/UCi) is an independent risk factor for stone formation, rather than hypocitraturia
Summary
The prevalence of urolithiasis is increasing around the world, especially among children.[1]. The gold standard for the diagnosis of hypocitraturia is a 24-hour urine collection and it is defined as urinary citrate excretion < 320 mg (1.67 mmol) per 24 hours for adults.[6] In children, 24-hour urine collections are notoriously unreliable.[7] age-dependent reference intervals for urinary citrate to creatinine ratios (UCi/UCr) have been established,[8] our own experience of the diagnostic yield of hypocitraturia to differentiate SF from non-SF (NSF) has been low. Höbarth and Hofbauer suggested a limited value for UCi/UCr.[9]
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