Purpose: Hypercalciuria is a risk factor for nephrolithiasis. We hypothesized that children with recurrent stones in 1 but not both kidneys and a normal 24-hour bladder urine calcium-to-creatinine ratio might exhibit isolated hypercalciuria of the affected kidney. Materials and Methods: Patients 18 years or younger with symptomatic urolithiasis who had undergone ureteroscopic stone removal were included. All subjects underwent 24-hour bladder urinalysis. Subjects with an increased urine calcium-to-creatinine ratio from the 24-hour urine collection were excluded. The 4 subject cohorts defined were 1) single stone episode in 1 kidney, 2) single stone episode in both kidneys, 3) recurrent stone episodes on 1 side and 4) recurrent stone episodes on both sides. All urine collections were obtained at ureteroscopy. Urine was obtained from the bladder and from the renal pelvis of the kidney forming the stone. Spot urine calcium-to-creatinine ratio was determined from these samples. Results: A total of 329 patients were included. Nine of 74 subjects (12%) with recurrent stone episodes on 1 side had increased spot urine calcium-to-creatinine ratio from the affected kidney. No patients in the other cohorts had increased spot urine calcium-to-creatinine ratio. Patients who formed recurrent stones in 1 kidney had increased spot urine calcium-to-creatinine ratio in the affected kidney vs other stone formers (ANOVA p <0.001). Conclusions: Unilateral hypercalciuria can occur in children with normal calcium levels in bladder urine. Unilateral hypercalciuria should be considered as a risk factor for nephrolithiasis in children with recurrent stone episodes in 1 kidney only.
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