Clinical and biochemical profile of patients with “pure” uric acid nephrolithiasis compared with “pure” calcium oxalate stone formers

Abstract

The purpose of the present study was to compare the clinical characteristics of "pure" uric acid (UA) stone formers with that of "pure" calcium oxalate (CaOx) stone formers and to determine whether renal handling of UA, urinary pH, and urinary excretion of promoters and inhibitors of stone formation were different between the two groups. Study subjects comprised 59 patients identified by records of stone analysis: 30 of them had "pure" UA stones and 29 had "pure" CaOx nephrolithiasis. Both groups underwent full outpatient evaluation of stone risk analysis that included renal handling of UA and urinary pH. Compared to CaOx stone formers, UA stone formers were older (53.3 +/- 11.8 years vs. 44.5 +/- 10.0 years; P = 0.003); they had higher mean weight (88.6 +/- 12.5 kg vs. 78.0 +/- 11.0 kg; P = 0.001) and body mass index (29.5 +/- 4.2 kg/m(2) vs. 26.3 +/- 3.5 kg/m(2); P = 0.002) with a greater proportion of obese subjects (43.3% vs. 16.1%; P = 0.01). Patients with "pure" UA lithiasis had significantly lower UA clearance, UA fractional excretion, and UA/creatinine ratio, with significantly higher serum UA. The mean urinary pH was significantly lower in UA stone formers compared to CaOx stone formers (5.17 +/- 0.20 vs. 5.93 +/- 0.42; P < 0.0001). Patients with CaOx stones were a decade younger, having higher 24-h urinary calcium excretion (218.5 +/- 56.3 mg/24 h vs. 181.3 +/- 57.1 mg/24 h; P = 0.01) and a higher activity product index for CaOx [AP (CaOx) index]. Overweight/obesity and older age associated with low urine pH were the principal characteristic of "pure" UA stone formers. Impairment in urate excretion associated with increased serum UA was also another characteristic of UA stone formers that resembles patients with primary gout. Patients with pure CaOx stones were younger; they had a low proportion of obese subjects, a higher urinary calcium excretion, and a higher AP index for CaOx.

Nephrolithiasis among male patients with newly diagnosed gout

“…Patients with pure calcium oxalate stones were younger; they had a low proportion of obese subjects and higher urinary calcium. 16 Conventionally, BMI was stratified as normal (<25 kg/m 2 ), overweight (25-29.9 kg/m 2 ), or obese (≥30 kg/m 2 ). In males, the proportion of uric acid stones gradually increased with BMI, from 7.1% in normal BMI to 28.7% in obese subjects.…”

An Update on the Changing Epidemiology and Metabolic Risk Factors in Pediatric Kidney Stone Disease

“…However, increasing uric acid crystallization may promote heterogeneous nucleation of CaOx, possibly leading to increased risk for CaOx stones in obese individuals (66). A number of studies have shown that overweight and obese adults may be at higher risk for kidney stones and have urine chemistry predisposing to the formation of calculi (66 -70), whereas other studies have not shown as clear a link (71)(72)(73)(74).…”

Serum uric acid in US adolescents: distribution and relationship to demographic characteristics and cardiovascular risk factors

“…It is becoming apparent that UA homeostasis and its relationship with health and disease is complex. Elevated serum UA is associated with hypertension (HTN), as well as with diabetes, cardiovascular disease, endothelial dysfunction, obesity, metabolic syndrome, nephrolithiasis, intellectual disabilities, and all-cause mortality (1)(2)(3)(4)(5)(6)(7)(8). On the other hand, some recent investigations provide evidence that UA may be beneficial as an antioxidant/freeradical scavenger in certain patient groups (9)(10)(11).…”