From collection to correction: Can serial 24-hour urine collections demonstrate improved urinary stone parameters?

Objectives: To determine whether serial 24-hour urine collections from the same patient over time result in improved stone risk parameters. Patients and Methods: Using a 24-hour urinalysis database, 1832 tests from 688 patients collected over a 10-year period were retrospectively reviewed. Patients included in the analysis had a minimum follow-up of 2 years and at least three 24-hour urine collections. Changes in risk parameters were evaluated over time with each patient acting as their own control. Statistical analysis was performed using repeated measures ANOVA with a Greenhouse-Geisser correction and post-hoc analysis with Bonferroni correction. Significance level was set as p < 0.05. Results: A total of 225 patients had at least three 24-hour urine collections, of which 48% were female. From the first to the second 24-hour urine collections, volume and supersaturation of CaOx, CaP and UA all significantly improved (p < 0.05). From the second to the third collection, only the supersaturation of CaP significantly improved (p < 0.05). Approximately half of the patients continued to see improvement in stone risk parameters between the second and third urine collection. Conclusion: Serial 24-hour urine collections performed at 6-month or greater intervals were significantly associated with improvements in stone risk parameters. This study suggests that serial collections can aid in the correction of urinary stone parameters and should be considered in active stone formers.