<p><strong>In adult patients with a history of struvite stones, clinicians should recommend a fluid intake sufficient to produce a urinary volume of at least 2.5 L (85 oz) daily. (<em>Expert Opinion</em>)</strong></p>
Discussion
Discussion
<p>It is not clear that metabolic evaluation with 24-hour urine testing is of benefit in patients with pure struvite or struvite/carbonate apatite stones, as stone formation presumably derives from the urinary changes induced by repeated infection with urease-producing bacteria. On the other hand, mixed stones containing a struvite component may reflect a nidus of metabolic stone crystals in which struvite crystal formation occurs within the appropriate milieu promoted by repeated infection with urease-producing bacteria. Lingeman et al. found that among 21 patients with “infection stones,” only 2 of 14 patients (14%) with pure struvite (struvite with or without carbonate apatite) stones versus 7 of 7 patients (100%) with mixed stones (struvite with or without carbonate apatite plus calcium oxalate) had metabolic abnormalities identified on 24-hour urine testing, suggesting that metabolic evaluation of patients with pure infection stones may be unnecessary.<sup>222</sup> However, Iqbal et al. reported metabolic abnormalities in 4 of 7 patients (57%) with pure struvite stones versus 26 of 32 patients (81%) with mixed struvite stones, concluding that metabolic evaluation in all patients with pure or mixed infection stones may be warranted.<sup>223</sup></p>
<p>Regardless of stone composition, higher urine volumes reduce urinary saturation of stone-forming salts and likely reduce the risk of stone recurrence. Although no clinical trials have evaluated the benefit of high fluid intake in reducing struvite stone recurrence, and struvite stone formation is primarily driven by urease production associated with recurrent UTIs due to urease-producing bacteria, the Panel extrapolated the benefit of high fluid intake and urine volume to include patients with struvite stones.</p>