title: 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.
authors.affiliation: Instituto de Investigaciones Metabólicas, Universidad del Salvador, Libertad 836 1 piso, Buenos Aires 1012, Argentina. negri@casasco.com.ar
authors.forename: Armando Luis
authors.initials: AL
authors.lastname: Negri
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Spivacow
authors.forename: Elisa
authors.initials: E
authors.lastname: Del Valle
authors.forename: Irene
authors.initials: I
authors.lastname: Pinduli
authors.forename: Alicia
authors.initials: A
authors.lastname: Marino
authors.forename: Erich
authors.initials: E
authors.lastname: Fradinger
authors.forename: Jose Ruben
authors.initials: JR
authors.lastname: Zanchetta
mesh_terms: D000328:Adult; D017668:Age of Onset; D002129:Calcium Oxalate / Q000378:metabolism* / Q000652:urine; D005260:Female; D006801:Humans; D007674:Kidney Diseases / Q000453:epidemiology / Q000378:metabolism* / Q000652:urine; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D053040:Nephrolithiasis / Q000378:metabolism*; D014527:Uric Acid / Q000378:metabolism* / Q000652:urine