Document Detail

Citric acid or citrates in urine: which should we focus on in the prevention of calcium oxalate crystals and stones?
MedLine Citation:
PMID:  12389124     Owner:  NLM     Status:  MEDLINE    
In order to distinguish between normocitraturia and hypocitraturia, the 24 h urine excretion value of citric acid is evaluated in relation to the established limit value of 2.5 mmol/day. We propose changing this widely-used excretion value to a "minimum contribution" of citric acid to the total urine's ionic strength, since the inhibitory effect of citric acid on crystallization depends on citrate anions being available to complex calcium ions or to associate with the crystal surface. A total of 71424 h-urine samples, taken from 74 healthy persons and 58 calcium stone formers, were investigated for pH, citric acid concentration ([CA]), and related relative calcium oxalate supersaturation (RS). Based on the Henderson-Hasselbalch-equation, the individual concentrations of the differently charged citrate anion species in each of the urines were calculated from the urinary pH and [CA]. From the anion concentrations determined, the contribution of the urine's citric acid to the total urine's ionic strength, ISCA, was calculated. Referring to the limit value of 2.5 mmol/day and assuming an average urine volume of 1.5 l/day, a hypothetical concentration limit of 1.67 mmol/l can be obtained. Grouping the samples into "stone-formers" and "non-stone-formers" as well as into three different ranges of RS revealed: (1). that the groups' median [CA]-values were below 1.67 mmol/l, and (2). that [CA] was not inversely associated with the risk of stone formation. Within the pH-range of 5 and 7, the ISCA-values which are related to, for example, [CA]=1.67 mmol/l, vary considerably by a factor of nearly three between 2.48 mmol/l and 6.64 mmol/l. The use of a fixed citric acid excretion level for the distinction of normocitraturia from hypocitraturia does not take into account the different citrate species which actually modify the urine's crystallization behaviour. The proposed ISCA approach takes this fact into consideration. From this parameter, a desirable "minimum impact of citric acid" can be derived. In a first approach, a potential ISCA-limit value, which currently distinguishes between urines indicated by a "normo-protective" impact and those indicated by a "hypo-protective" impact with respect to calcium oxalate precipitation, may be set at 2.48 mmol/l.
Norbert Laube; Brigitte Jansen; Albrecht Hesse
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2002-08-30
Journal Detail:
Title:  Urological research     Volume:  30     ISSN:  0300-5623     ISO Abbreviation:  Urol. Res.     Publication Date:  2002 Oct 
Date Detail:
Created Date:  2002-10-21     Completed Date:  2003-06-25     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0364311     Medline TA:  Urol Res     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  336-41     Citation Subset:  IM    
Division of Experimental Urology, Department of Urology, Bonn University, Sigmund-Freud-Strasse 25, 53105 Bonn, Germany,
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MeSH Terms
Anions / urine
Calcium Oxalate / chemistry*,  urine
Case-Control Studies
Citrates / urine*
Citric Acid / urine*
Hydrogen-Ion Concentration
Osmolar Concentration
Urinary Calculi / prevention & control*
Reg. No./Substance:
0/Anions; 0/Citrates; 25454-23-3/Calcium Oxalate; 77-92-9/Citric Acid

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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