Non-infectious phosphate renal calculi: Fine structure, chemical and phase composition

Abstract

Background. Chemical composition of internally non-homogeneous phosphate stones should be related to the conditions prevailing during the formation of each individual part. Objective. The object of this paper was to provide a detailed study of phosphate stone composition on the micro- and macro-scales. Methods. Fine inner structure, chemical and phase composition of 10 phosphate calculi from different patients were determined by chemical (wet) analysis, observation by scanning microscope, semi-quantitative determination of Ca, Mg, P and C by energy dispersive X-ray and by X-ray diffraction. Results. Eight calculi are formed by amorphous calcium phosphate and two by hydroxyapatite. Magnesium was inversely related to Ca/P ratio. Point chemical composition of solid phase varies in wide limits, i.e. composition of calculus interior is highly inhomogeneous on the microscale. All studied calculi contained an abundance of organic matter incorporated in their volume; the content of carbon was double the calcium content in molar quantities. Conclusions. Phosphate renal calculi with the low Ca/P molar ratio predominantly consist of amorphous calcium phosphate whereas those with a high Ca/P molar ratio are composed of poorly crystalline hydroxyapatite which can be partially carbonated. Magnesium may be an inhibitor of HAP formation from urine. Abundant organic matter incorporated into the calculus volume indicates its decisive role at stone formation. Variable point composition of stones implies widely varying conditions during their development.

Key Words::

• Kidney calculi
• hydroxyapatite
• fine structure
• composition
• EDX
• x-ray diffraction

Acknowledgements

This work was supported by Fundació Barceló (Ref. 1458/2007) and project grant CTQ 2010-18271 from the Ministerio de Ciencia e Innovación del Gobierno de España. I.G. expresses her appreciation to the Conselleria d'Innovació i Energia del Govern de les Illes Balears (Spain) for a fellowship supporting her work. O.S. is grateful to the University of the Balearic Islands for a grant which made this cooperation possible.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.