During the initial metabolic evaluation, the need for one versus two 24-hour urine collections is debated. While data suggest that mean urine chemistry measures are similar on consecutive samples, it remains unclear how much, if any, information is lost when only one is collected.
Using analytical files from Litholink Corporation® (1995 to 2013), we identified adults with kidney stones, who underwent initial metabolic testing. Next, we determined the subset of patients that collected two 24-hour urine samples with urine creatinine varying by 10% or less during a seven-day time window. We then examined the degree of variability in urine chemistry profiles. Specifically, we calculated the mean absolute value of the difference between samples, as well as the percent difference, for individual urine parameters.
We identified 70,192 patients meeting our eligibility criteria. While the overall means for individual urine parameters did not vary between samples, the percent difference between the samples varied widely. For example, nearly one in three patients had a 30% or more difference in urine calcium and volume between two consecutive samples. We noted that inconsistencies between samples often involved multiple parameters. For instance, 29% and 25% of patients had a 20% difference in two and three or more parameters, respectively.
We observed substantial differences between consecutive 24-hour urine samples that could affect clinical decision-making. In light of these findings, clinicians must weigh the information lost from only one collection versus the burden to the patient of collecting two.
The Journal of urology. 2016 Apr 29 [Epub ahead of print]
Abdulrahman F Alruwaily, Casey A Dauw, Maggie J Bierlein, Phyllis Yan, John R Asplin, Khurshid R Ghani, J Stuart Wolf, John M Hollingsworth
Department of Surgery, College of Medicine, Al-Imam Muhammad Ibn Saud Islamic University (IMSIU), Riyadh, Saudi Arabia., Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, MI., Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, MI., Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, MI., Litholink Corp®, Laboratory Corporation of America® Holdings Chicago, IL., Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, MI., Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, MI., Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, MI. Electronic address: .