Urinary calcium-to-citrate ratio predicts kidney stone risk in children under the age of two years

The urinary calcium-to-citrate (Ca/Cit) ratio has emerged as a useful indicator of lithogenic risk in older children; however, no reference data exist for infants and toddlers. This study aimed to evaluate whether the spot Ca/Cit ratio can distinguish stone-forming from non-stone-forming children under 24 months of age and to assess its diagnostic performance compared with conventional urinary markers.

This retrospective single-center study included 181 children aged 1-24 months who underwent metabolic evaluation and ultrasonography at their first presentation to a tertiary pediatric nephrology clinic between 2012 and 2024. Based on urinary calcium excretion and ultrasonographic findings, participants were categorized as normocalciuric stone-free controls (n = 57), hypercalciuric stone-formers (n = 29), or non-hypercalciuric stone-formers (n = 95). Spot urine calcium, citrate, and related biochemical ratios were analyzed. The diagnostic accuracy of the Ca/Cit ratio for predicting stones was assessed using receiver operating characteristic (ROC) analysis.

The Ca/Cit ratio differed significantly across groups, with the highest levels observed in hypercalciuric stone-formers (0.46 mg/mg) compared with controls (0.17 mg/mg; p < 0.001) and non-hypercalciuric stone-formers (0.31 mg/mg; p < 0.001). A Ca/Cit threshold > 0.23 mg/mg (≈ 1.10 mmol/mmol) demonstrated moderate diagnostic ability for stone detection (AUC 0.695; 95% CI 0.613-0.785), yielding 66.1% sensitivity and 63.2% specificity. Age showed no meaningful correlation with Ca/Cit values. Normocalciuric stone-free children provided an age-appropriate reference distribution for Ca/Cit ratios.

In infants and toddlers evaluated for suspected urinary stone disease, the Ca/Cit ratio offers moderate discriminatory power and may serve as a practical adjunctive marker of stone risk. A ratio > 0.23 mg/mg (≈ 1.10 mmol/mmol) appears to indicate increased lithogenic potential. Larger prospective studies are needed to validate reference intervals and refine clinically applicable cut-off values for this young age group.