Elsevier

Clinica Chimica Acta

Volume 263, Issue 1, 4 July 1997, Pages 43-55
Clinica Chimica Acta

Simple test to evaluate the risk of urinary calcium stone formation

https://doi.org/10.1016/S0009-8981(97)06554-6Get rights and content

Abstract

A simple test to evaluate the capacity of a urine to crystallize calcium salts is presented. The test is based on the fact that if a non-protected non-renewed surface remains in contact with a urine, sooner or later the contained supersaturated substances crystallize on it. Thus, by using an adequate surface, it is possible to derive a period within which a normal urine does not crystallize whereas a lithogenic urine induces the growth of calcium salts. The test was applied to urines of oxalocalcic stone-formers and healthy people and showed an excellent discrimination between clearly abnormal and healthy urines. Semiologic analysis of the data is also included.

Introduction

The formation of renal calculi in practically all cases, must be attributed to a combination of diverse factors. These factors may be classified into two main groups: (1) factors related to urine composition and (2) factors related to renal morphoanatomy.

Urine is a metastable system in which several substances capable of crystallizing and generating renal calculi coexist. Normally, these substances are in supersaturated conditions and the ease of crystallization depends on the degree of supersaturation, the presence of promoter substances (heterogeneous nucleants) and the level of inhibitors of crystallization. On the other hand, the presence of cavities with low urodynamic efficacy that, as a consequence, retain the urine for a long time, and alterations of the epithelium that covers the renal papillae (damaged anti-adherent glycosaminoglycan layer, necrosis, etc.), are the main factors linked to the renal structure that favour the calculi formation. Usually, to develop renal calculi, the coexistence of factors from both main groups is necessary.

Several procedures have been previously established to evaluate the crystallization properties of a urine 1, 2, 3, 4. Here a very simple test to evaluate the capacity of a urine to crystallize calcium salts is presented. The test is based on the fact that urines which tend to form renal calculi have a higher capacity to generate calcium salts than non-lithogenic urines. Thus, a healthy urine does not produce crystals in the proposed test whereas a lithiasic one does.

Section snippets

Materials and methods

The test is based on the fact that if a non-protected non-renewed surface remains in contact with a urine, sooner or later the contained supersaturated substances crystallize on it. The ease of crystallization depends on the balance of the forces that drive it (supersaturation and heterogeneous nucleants) and those that appose it (crystallization inhibitors). Thus, by using an adequate surface, it is possible to derive a period within which a normal urine does not crystallize whereas a

Results

A total of 32 healthy people and 92 patients with oxalocalcic urolithiasis were selected to evaluate the suitability of the proposed test. Results are shown in Table 2, Table 3, where biochemical measurements are also included.

Between 75% (urine 1) and 83% (urine 2) of the healthy group gave negative results (Table 2), 100% of healthy people with normal urine gave a negative result when the test was applied, whereas between 50% (urine 2) and 100% (urine 1) of healthy people with hypercalciuric

Discussion

The test is based on the fact that when a non-renewed, non-protected surface remains in contact with urine, sooner or later the contained supersaturated substances crystallize on it 6, 7. Several substances (different calcium phosphate salts and paraffin) were tested as substrates to induce the crystallization of salts when in contact with urine and showed similar results. Paraffin was selected as the optimum substrate because it permits an easier evaluation of the calcium crystallized on it by

Acknowledgements

Financial support by the D.G.I.C.Y.T. (grant PB 92-0249) is gratefully acknowledged.

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