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[Value of infrared spectrophotometry morpho-constitutional analysis of double J stent encrustations for indirect determination of urinary stone composition].

INTRODUCTION
A single stone analysis is necessary during the patient's clinical history in order to institute specific drug treatment and health and dietary measures to prevent stone recurrence. In practice, only one in every two stones is recovered for morpho-constitutional analysis. The objective of this study was to determine the place of double J stent encrustation analysis for indirect determination of stone composition.


MATERIAL AND METHODS
Double J stents and stones from all patients treated in the same centre over 24 months were consecutively analysed by infrared spectrophotometry. The correlation coefficient 1, evaluating the concordance between the composition of stones and double J stent encrustation was estimated statistically by SPSS 12.0 software (0<1<1; 1=0: no concordance; 1=1: perfect concordance).


RESULTS
45 males and 27 females with a mean age of 45.3 years (range: 29-70) were included Double J stents were placed for: febrile obstruction (N=52; 72%), acute renal colic (N=15; 21%) and impaired renal function (N=5; 7%). Calculated values for 1 were: 0.78 for the concordance between the predominant constituent of the stone and the encrustation (N=72; p < 0.0005); 0.91 for the concordance between the nature of the encrustation of the upper loop and that of the lower loop of the stent (N=30, p < 0.0005).


CONCLUSION
The composition of mineral encrustation of double J stents is a good marker of stone formation. This constitutes an alternative method that can be used by urologists when no stone is available for spectrophotometric analysis.