Elsevier

Urology

Volume 85, Issue 2, February 2015, Pages 296-298
Urology

Endourology and Stones
100% Uric Acid Stone Formers: What Makes Them Different?

https://doi.org/10.1016/j.urology.2014.10.029Get rights and content

Objective

To identify what risk factors on 24-hour urinalysis, if any, predispose patients to have higher percentages of uric acid (UA) stone composition in their stones, with specific emphasis on patients with pure UA stones.

Methods

We retrospectively identified 308 patients from review of a kidney stone analysis database. Patients were grouped according to the percentage UA composition: 10%-20%, 30%-50%, 60%-90%, and 100% UA. Data were extracted from 24-hour urine collections and serum chemistries. Patients taking allopurinol, citrates, or thiazide diuretics were excluded.

Results

The percentage UA stone composition increased as patients became older (P = .05) or heavier (P <.001). Gender did not impact the percentage of UA in stones. Although a higher serum UA level was associated with higher UA stone composition (P <.0006), urinary UA levels did not correlate (P = .1). In contrast, urinary pH correlated significantly with higher UA stone composition (P = .03).

Conclusion

Older and heavier patients with higher serum UA levels are more likely to have a pure UA stone. This information combined with traditional predictors (urine pH, radiopacity of stone, and Hounsfield units) may help identify those most likely to respond to dissolution therapy.

Section snippets

Design

We identified patients from a retrospective review of an institutional review board–approved kidney stone database. Patients who had a UA component to their stone and who had completed a 24-hour urine stone risk profile within 3 months of their stone analysis were selected for the study. Twenty-four-hour urine profiles were performed by the Cleveland Clinic Department of Laboratory Medicine. Specimens were refrigerated before analysis, which was subsequently performed at 37°C with phosphate

Results

A total of 308 patients were identified (65% male) with a mean age of 57 ± 12 years and mean body mass index (BMI) of 31 ± 7.8 kg/m2. Overall, 91 patients had 100% UA stones, 55 had 60%-90% UA stones, 12 had 30%-50% UA stones, and 150 had 10%-20% UA stones (Table 1). The most common secondary component of non-100% UA stones was calcium oxalate. Patients with 100% UA stones were older than those with 10%-20% UA stones (60 vs 55 years; P = .05). Patients had a higher BMI if their stone was 100%

Comment

Previous studies have used a combination of radiographic and urinary parameters in an attempt to define stone composition in the absence of a direct analysis of stone composition from a stone that has been surgically removed or spontaneously passed.8, 9, 10 However, it has also been demonstrated that these measures, such as computed tomography attenuation values, vary widely depending on the scanner model used.11 These studies have used varying percentages of UA stone composition; none focused

Conclusion

Patients with 100% UA stones are older, heavier, and have a higher serum UA level and lower urinary pH than patients with mixed-stone composition. Urinary UA is not significantly different among groups. Defining associations such as these will enable development of clinical algorithms, in combination with radiographic appearance that facilitate prediction of the probability a patient has a 100%-UA stone. This will then enable the clinician to counsel them more accurately on their treatment

References (16)

There are more references available in the full text version of this article.

Cited by (21)

  • Comprehensive Nomogram for Prediction of the Uric Acid Composition of Ureteral Stones as a Part of Tailored Stone Therapy

    2022, European Urology Focus
    Citation Excerpt :

    However, the guidelines give no recommendations in most common clinical scenarios for which uric acid calculi are suspected but not yet confirmed by stone analysis. Several nomograms and screening tools have been developed to assess the probability of uric acid stone composition and to identify patients who might benefit from chemolitholysis [9–11]. Multiple combinations of factors were investigated in previous studies for the best possible prediction of uric acid stone composition.

  • Long-term Recurrence Rates in Uric Acid Stone Formers With or Without Medical Management

    2019, Urology
    Citation Excerpt :

    To qualify for inclusion into this specific study, patients from our UA subset were required to be completely stone-free bilaterally postprocedure by CT scan and have (1) stone analysis showing ≥30% UA mineral content; (2) at least 1 baseline 24-hour urine collection; (3) ≥6 months of clinic follow-up; and (4) at least 1 surveillance CT scan ≥6 months following postprocedure scan. We used the methodology of Reichard13 to categorize UA stone mineral phenotypes as “mixed” if UA content was between 30% and 89% or “pure” if UA content was 90% and 100%. We classified individuals as “adherent” if they reported adherence to medications during clinic charting and had refill documentation by hospital or pharmacy electronic medical records.

  • Medical therapy for nephrolithiasis: State of the art

    2018, Asian Journal of Urology
    Citation Excerpt :

    Combining these demographics with stone size and Hounsfield units on CT scan may contribute to better diagnostic accuracy in identifying patients with pure uric acid stones who may be successfully treated with dissolution therapy. Complete dissolution may occur in as little as 6 weeks to 6 months or more [124,125], likely due to the varying percentages of uric acid stone composition [123]. Cystinuria is a rare inherited disorder in the renal and intestinal transport of the dibasic amino acids, caused by mutations in the SLC3A1 and/or SLC7A9 genes [126].

  • Nephrolithiasis

    2016, Hospital Medicine Clinics
    Citation Excerpt :

    For patients with no urinary abnormalities but with recurrent stones, potassium citrate and thiazides should be offered.19 In the case of uric acid stones, the goal is to use medications to increase urinary pH. In these patients, the low urinary pH, rather than hyperuricosuria, precipitates uric acid stones.5 For struvite stones, the mainstay of therapy is minimally invasive stone removal.

View all citing articles on Scopus

Financial Disclosure: The authors declare that they have no relevant financial interests.

View full text