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Licensed Unlicensed Requires Authentication Published by De Gruyter July 5, 2005

Effects of urine dilution on quantity, size and aggregation of calcium oxalate crystals induced in vitro by an oxalate load

Angela Guerra , Franca Allegri , Tiziana Meschi , Giuditta Adorni , Beatrice Prati , Antonio Nouvenne , Almerico Novarini , Umberto Maggiore , Enrico Fiaccadori and Loris Borghi


Increasing urinary volume is an important tool in the prevention of calcium renal stones. However, the mechanism of how it actually works is only partially understood. This study aimed at assessing how urine dilution affects urinary calcium oxalate crystallization. A total of 16 male idiopathic calcium oxalate (CaOx) stone-formers and 12 normal male subjects were studied and 4 h urine samples were taken twice, under low (undiluted urine) and high hydration conditions (diluted urine). An equal oxalate load (1.3mmol/L) was added to both types of urine and the crystallization parameters were assessed. In both stone-formers and normal subjects, the crystallization processes were significantly (p<0.05 or less) more marked in the undiluted urine than in the diluted urine in terms of: a) total quantity of calcium oxalate dihydrate (COD) and calcium oxalate monohydrate (COM) crystals; b) total quantity of crystalline aggregates; and c) aggregation index (i.e., ratio between the area occupied by crystalline aggregates and the area occupied by all the crystals present). The comparison between stone-formers and normal subjects showed that the greatest difference was for the size of COD crystals, which were larger in the urine of the stone-formers. A further important finding was an inverse relationship between changes in urinary volume and in the aggregation index (r=–0.53, p=0.004). In conclusion, urine dilution considerably reduces crystallization phenomena induced in vitro by an oxalate load in both calcium stone-formers and normal subjects.

Corresponding author: Loris Borghi MD, Dipartimento di Scienze Cliniche, Università di Parma, Via Gramsci 14, 43100 Parma, Italy Phone: +39-0521-702007, Fax: +39-0521-940993,


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Received: 2005-1-24
Accepted: 2005-3-30
Published Online: 2005-7-5
Published in Print: 2005-6-1

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