How many 24-hour urine collections does it take to screw in a proper therapeutic plan to prevent recurrent urolithiasis? One.

In this study of 777 urolithiasis patients, the authors note that the difference among sodium, calcium, and oxalate in two 24-hour urine samples spaced 3 days apart was only 2-4% - not enough to really alter a diagnosis. These findings concur with earlier recommendations from Dr. Pak's laboratory at Southwestern Medical School, albeit on a smaller sample size of 225 patients, reported in 2001.1 I fully concur with the authors' recommendations, and for the past decade have obtained only a single 24-hour sample. Based on the results of that sample, my routine is to begin therapy (which can vary from dietary to medications) and then obtain a follow-up 24-hour urine sample in 6 weeks. If that shows the desired beneficial effect, then follow-up is with low dose noncontrast CT of the kidneys at 6 months and then annually. Only if there is evidence of new stone formation or growth of a pre-existing stone will I obtain any further 24-hour urine samples.

Reference:

1Pak, C. Y., Peterson, R., and Poindexter, J.R.: J. Urol. 165: 378, 2001.

Castle SM, Cooperberg MR, Sadetsky N, Eisner BH, Stoller ML
J Urol. 2010 Aug;184(2):579-83 doi: 10.1016/j.juro.2010.03.129

UroToday Medical Editor Ralph V. Clayman, MD

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