Editorial Comment on: Age,Body Mass Index,and Gender Predict 24-Hour Urine Parameters in Recurrent Idiopathic Calcium Oxalate Stone Formers by Otto et al . (From: Otto BJ,Bozorgmehri S,Kuo J,et al. J Endourol 2017;31:1335–1341)

In this article, Brandon and colleagues have shown that age, gender, and body mass index can be used to predict 24-hour urine abnormalities in a cohort of recurrent calcium oxalate stone formers. The intent of the study was to determine whether these data could be used to develop a risk prediction tool that may obviate the need for formal 24-hour urine testing. This is not the first study to question the utility of 24-hour urine testing. Hsi et al. ¹ recently published an article examining the role of 24-hour urine collection in the prevention of kidney stone recurrence. They evaluated cited evidence for the American Urological Association (AUA) and European Association of Urology (EAU) guidelines on metabolic stone prevention, conducted a MEDLINE search of controlled studies of dietary and pharmacologic intervention, and specifically examined the placebo arms of these studies. Several limitations of 24-hour urine testing were reported including complexity of interpretation, the need for repeat collection, and the inability of individual urine and supersaturation parameters to predict stone recurrence. Ultimately, the authors concluded that the benefit of 24-hour urine testing is not well established in recurrent stone formers. If this is true, then maybe it is a good thing because a recent population-based study found that the prevalence of metabolic testing in high-risk kidney stone formers was only 7.4%. ²

So, with this new information, can we advocate abolition of 24-hour urine testing? I would suggest we may be throwing the baby out with the bath water. The 2014 AUA guidelines on the medical management of kidney stones state “Clinicians should perform additional metabolic testing in high-risk or interested first-time stone formers and recurrent stone formers” (evidence strength Grade B). ³ This guideline statement is based, in part, on a prospective trial that demonstrated that selective dietary recommendations based on 24-hour urine data were more effective than general dietary measures in preventing stone recurrence. ⁴ I often wonder whether the poor compliance we see with 24-hour urine testing is more because of the patient or the provider. In my own practice, a stone clinic environment, where the potential benefits of 24-hour urine testing are emphasized, patients not only seem interested but more often than not actually complete the testing. We take a “know your numbers” approach that has demonstrated effectiveness in other chronic diseases such as diabetes mellitus and hypertension. Sure, not every patient will be this engaged and it is for these patients that the investigations by Brandon and colleagues make a lot of sense.

So back to the question again, should we advocate against formal 24-hour urine testing? I believe the answer is no. Just as the guidelines recommend, 24-hour urine testing should be offered to high-risk stone formers and interested first-time stone formers. However, exploring alternative strategies to help the individuals who are either unwilling, unable, or uninterested in this testing is not only novel but also progressive. It is difficult to know whether the results in this study can be generalized to the entire population as there are clearly regional differences in diet, climate, and environment. Furthermore, these results would need to be validated before using them to recommend pharmacologic intervention. In the end, exploring the question as to the utility of 24-hour urine testing is worthwhile because it underscores the need for the funding of further research and comparative effectiveness trials surrounding dietary and medical management of nephrolithiasis.