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Differences in 24-hour urine composition between white and Asian/Pacific Islander stone-formers
Brian H. Eisner, MD1, Sima P. Porten, MD2, Seth Bechis, BA2, Marshall L. Stoller, MD2.
1Massachusetts General Hospital, Boston, MA, USA, 2University of California, San Francisco, San Francisco, CA, USA.

BACKGROUND: Little is known about the relationship between race and 24-hour urine composition. The purpose of this study was to examine the differences in 24-hour urine composition between white and Asian/Pacific Islander stone-formers who presented to a metabolic stone clinic.
METHODS: A retrospective review of a database of 24-hour urinalyses from a metabolic stone clinic was performed. Patients who marked “white” or “Asian/PI” as their race on demographic survey and were ≥ 18 years of age were included in the study. Outpatient clinic and hospital records and 24-hour urine chemistry data were analyzed. Univariate analysis and multivariate linear regression was performed to determine the relationship between race and 24-hour urine composition. Multivariate analysis adjusted for potential confounders including age, gender, body mass index, hypertension, diabetes, thiazide use, potassium citrate use, and 24-hour urine constituents (calcium, oxalate, citrate, uric acid, potassium, magnesium, phosphate, and sulfate). Patients with inadequate urine collections (males with urine creatinine < 800 mg/day, women with urine creatinine < 600 mg/day) were excluded.
RESULTS: Three-hundred seventy-one (371) white patients and 91 Asian/PI patients were included for analysis. On univariate analysis, compared with white patients, Asian/PI patients excreted significantly greater amounts of uric acid (0.77 versus 0.68 g/day, p=0.01) and significantly lower amounts of citrate (438.6 versus 604.1 mg/day, p<0.001), magnesium (97.2 versus 111.0 mg/day, p=0.003), and phosphate (0.85 versus 1.02 g/day, p<0.001). Twenty-four hour urine volume, pH, and excretion of calcium, oxalate, potassium, sodium, and sulfate were not different between the 2 groups.Multivariate linear regression results were as follows: compared with white patients, Asian/PI patients excreted 0.1 g/day more uric acid (95% CI 0.06 - 0.13), 151.4 mg/day less citrate (95% CI -234.5 - -68.2), 8.7 mg/day less magnesium (95% CI -17.1 - -0.2), 0.09 g/day less phosphate (95% CI -0.14 - -0.04), and voided 0.21 L/day less volume (95% CI -0.40 - 0.01). Twenty-four hour urine pH, and excretion of calcium, oxalate, potassium, sodium, and sulfate were not different between the 2 groups.
CONCLUSIONS: Significant differences in 24-hour urine composition exist between white and Asian/PI stone-formers. Specifically, Asian/PI patients excreted significantly more uric acid and significantly less volume, citrate, and magnesium than white patients. These racial differences are important when considering medical and dietary therapy for patients with nephrolithiasis.


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