Improved 24-hour urine parameters associated with reduced symptomatic kidney stone recurrence

On-treatment 24-h urine testing rates are low outside of tertiary care centers. A common criticism is the paucity of evidence demonstrating the optimization of urinary parameters correlates with reduced stone recurrence. Using standard and novel analytic approaches, we sought to evaluate whether improvements in 24-h urine parameters associated with decreased symptomatic stone recurrence. Kidney stone patients who underwent multiple 24-h urine tests and had an initial parameter abnormality were identified from a prospective database. A novel 24-h urine severity score was calculated at both the initial and subsequent tests and used to stratify patients. Negative binomial regression was used to evaluate the impact of analyte changes on stone recurrence. Two hundred patients met inclusion criteria. Low voided volume, hypercalciuria, hyperoxaluria, hypocitraturia and low pH were identified in 56%, 28%, 40%, 49% and 35% respectively. Patients with hypercalciuria and hypocitraturia who consistently normalized these values showed decreased recurrence (p < 0.001). Increasing initial 24-h urine severity scores associated with increased stone recurrence (0.09, 0.18 and 0.31 stone events per year for the lowest, 25-75th and highest quartiles, p < 0.001). On multivariable analysis, severity score improvement or stabilization was associated with reduced risk of recurrence across all quartiles (RRR 0.319 to 0.591, all p < 0.001). Consistent control of 24-h urine parameters was associated with decreased stone recurrence. Not only did novel 24-h urine composite severity scores based on initial 24-h urines independently predict stone recurrence, improvements in this score over time also predicted decreased recurrence.