title: Biochemical and dietary factors of uric acid stone formation.
abstract: The aim of this study was to compare the clinical characteristics of "pure" uric acid renal stone formers (UA-RSFs) with that of mixed uric acid/calcium oxalate stone formers (UC-RSFs) and to identify which urinary and dietary risk factors predispose to their formation. A total of 136 UA-RSFs and 115 UC-RSFs were extracted from our database of renal stone formers. A control group of 60 subjects without history of renal stones was considered for comparison. Data from serum chemistries, 24-h urine collections and 24-h dietary recalls were considered. UA-RSFs had a significantly (p = 0.001) higher body mass index (26.3 ± 3.6 kg/m2) than UC-RSFs, whereas body mass index of UA-RSFs was higher but not significantly than in controls (24.6 ± 4.7) (p = 0.108). The mean urinary pH was significantly lower in UA-RSFs (5.57 ± 0.58) and UC-RSFs (5.71 ± 0.56) compared with controls (5.83 ± 0.29) (p = 0.007). No difference of daily urinary uric acid excretion was observed in the three groups (p = 0.902). Daily urinary calcium excretion was significantly (p = 0.018) higher in UC-RSFs (224 ± 149 mg/day) than UA-RSFs (179 ± 115) whereas no significant difference was observed with controls (181 ± 89). UA-RSFs tend to have a lower uric acid fractional excretion (0.083 ± 0.045% vs 0.107+/-0.165; p = 0.120) and had significantly higher serum uric acid (5.33 ± 1.66 vs 4.78 ± 1.44 mg/dl; p = 0.007) than UC-RSFs. The mean energy, carbohydrate and vitamin C intakes were higher in UA-SFs (1987 ± 683 kcal, 272 ± 91 g, 112 ± 72 mg) and UC-SFs (1836 ± 74 kcal, 265 ± 117, 140 ± 118) with respect to controls (1474 ± 601, 188 ± 84, 76 ± 53) (p = 0.000). UA-RSFs should be differentiated from UC-RSFs as they present lower urinary pH, lower uric acid fractional excretion and higher serum uric acid. On the contrary, patients with UC-RSFs show urinary risk factors more similar to those for calcium oxalate stones. The dietary approach in patients forming uric acid stones should be reconsidered with more attention to the quantity and quality of carbohydrate intake.
authors.affiliation: Urology Unit, Manzoni Hospital, Via dell'Eremo 9/11, 23900, Lecco, Italy. a.trinchieri@asst-lecco.it.
authors.forename: Alberto
authors.initials: A
authors.lastname: Trinchieri
authors.affiliation: IRCCS Ca' Granda Ospedale Maggiore Policlinico-University of Milan, Milan, Italy.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Montanari
mesh_terms: D000328:Adult; D000368:Aged; D015992:Body Mass Index; D002118:Calcium / Q000097:blood / Q000652:urine; D002129:Calcium Oxalate / Q000378:metabolism* / Q000652:urine; D000070601:Diet, Carbohydrate Loading / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007669:Kidney Calculi / Q000097:blood / Q000737:chemistry / Q000209:etiology* / Q000652:urine; D008297:Male; D008875:Middle Aged; D065667:Renal Elimination; D012189:Retrospective Studies; D012307:Risk Factors; D014527:Uric Acid / Q000097:blood / Q000378:metabolism* / Q000652:urine
chemical_list: D002129:Calcium Oxalate; D014527:Uric Acid; D002118:Calcium
keywords: Diet; Uric acid; Urinary calculi; Urinary pH