[Determination of urinary citrates by an alternative of Millan's method]

the physiopathological interest of the determination of urinary citrate lies primarily in its relationships to the lithiasic processes. Indeed, the citrate is a powerful complexing agent of calcium able to lower urinary supersaturation of oxalate and phosphate of calcium.

this study describes a revaluation of the determination of urinary citrates by the colorimetric method of Millan.

the principle of the method rests on the quantification of the yellow complex formed with iron chloride III and the urinary citric acid, measurable at 390 nm in acidic medium. All the conditions were combined to optimize it, while covering a satisfying field of measurement.

the evaluation of the modified method showed a good precision (repeatability: CV from 0,18 to 3,42%; intraserial reproducibility: CV from 1,87 to 3,44 %; interserial reproducibility: CV from 2,15 to 5,52%) and a very good accuracy. The field of measurement extends up to 17,0 mmol/L, with a limit of detection (L(D)) lowered to 0,2 mmol/L (Vs 1,48 mol/L for the original method). All analytical performances are improved by automation with a L(D) = 0,09 mmol/L and a limit of linearity extended to 18 mmol/L.

this modified, simple, fast, inexpensive and easily automatizable technique, seems to be reliable and especially more sensitive, adapting particularly to the detection of subjects suffering a deficit of citrate secretion, one of most significant inhibiting agent of lithiasis kidney formation.