The Role of the 24-Hour Urine Collection in the Prevention of Kidney Stone Recurrence.

PURPOSE: Kidney stone prevention relies on the 24-hour urine collection to diagnose metabolic abnormalities and direct dietary and pharmacological therapy. While its use is guideline supported for high risk and interested patients, evidence that the test can accurately predict recurrence or treatment response is limited. We sought to critically reassess the role of the 24-hour urine collection in stone prevention. MATERIALS AND METHODS: In addition to a MEDLINE® search to identify controlled studies of dietary and pharmacological interventions, evidence supporting the AUA (American Urological Association) and EAU (European Association of Urology) guidelines for metabolic stone prevention were evaluated. Additionally, the placebo arms of these studies were examined to assess the stone clinic effect, that is the impact of regular office visits without specific treatment on stone recurrence. RESULTS: The 24-hour urine test has several limitations, including the complexity of interpretation, the need for repeat collections, the inability to predict stone recurrence with individual parameters and supersaturation values, the unclear rationale of laboratory cutoff values and the difficulty of determining collection adequacy. Only 1 prospective trial has compared selective dietary recommendations based on 24-hour urine collection results vs general dietary instructions. While the trial supported the intervention arm, significant limitations to the study were found. Placebo arms of intervention trials have noted a 0% to 61% decrease in stone recurrence rate and a remission rate during the study of 20% to 86%. CONCLUSIONS: Whether all recurrent stone formers benefit from 24-hour urine collection has not been established. Additional comparative effectiveness trials are needed to determine which stone former benefits from selective therapy, as guided by the 24-hour urine collection.