WCE 2019: Urinary Metabolic Abnormalities in Patients with Pure vs. Mixed Uric Acid Stones

Abu Dhabi, United Arab Emirates (UroToday.com) Dr. Mantu Gupta wanted to compare patients who make pure uric acid stones to those who make mixed stones, defined as uric acid and calcium oxalate stones. The main aim of this study was to determine if these patient cohorts were similar or different, and what their metabolic abnormalities are. Uric acid stones can occur in three to four different combinations, and the association of calcium oxalate with urinary metabolic abnormalities has been extensively investigated.  However, little is known about the association between metabolic disturbances and pure uric acid stone formers. Dr. Gupta sought to better understand the differences between patients who formed pure uric acid stones and those who formed mixed stones by evaluating clinical and metabolic factors.

WCE 2019 pure UA stone and mixed UA stone formers

Dr. Gupta’s group prospectively collected on patients with urinary tract stones between 2012 and 2016. Patients were divided into two groups based on the degree of uric acid composition of their stones. Variables such as the diagnosis of metabolic syndrome and 24-hour urine collections were compared between the two groups. 81 patients were identified with 100% pure uric acid stones. No statistical difference was found between gender, age, BMI, and prior stone history. However, pure uric acid stone formers had a higher incidence of metabolic syndrome (23.1% vs 12.1%, respectively) and a higher incidence of diabetes (42.3% vs 35.8%, respectively).

Furthermore, there was a statistically significant difference in urinary pH between pure uric acid stones formers (5.43) versus mixed uric acid stone formers (5.72 (p =0.03). Urinary ammonia (39mg vs. 30mg, p = 0.02) and sulfate levels (53mg vs 43mg, p =0.05) were also statistically higher in the pure uric acid cohort.

In conclusion, Dr. Gupta and his team found that pure uric acid stone formers had higher incidences of metabolic syndrome, more acidic urine and higher urinary ammonia and sulfate levels. These findings likely reflect greater acidosis and protein intake in pure uric acid stone formers. Interestingly enough, the majority of pure uric acid stone formers did not demonstrate other metabolic factors such as hypercalciuria or hyperoxaluria that would inform stone prevention management. Dr. Gupta stressed that treatment with potassium citrate and diet modifications should address underlying issues of these patients’ calculus growth kinetics, mainly urine pH and hypercitraturia.

Presented by: Mantu Gupta, MD, Department of Urology, Icahn Mount Sinai School of Medicine, New York

Written by: Lillian Xie, BA, Department of Urology, University of California, Irvine, California at the 37th World Congress of Endourology (WCE) – October 29th-November 2nd, Abu Dhabi, United Arab Emirates