BERKELEY, CA (UroToday.com) - 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: (a) factors related to urine composition and (b) 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 papilla (calcium phosphate deposits as Randall’s plaques, necrosis, etc.), are the main factors linked to the renal structure that favor calculi formation. Usually, to develop renal calculi, the coexistence of factors from both main groups is necessary.
There are diverse methodologies to evaluate the global lithogenic capacity of a given urine. Several of these procedures are based on the combination of a number of particular biochemical urinary parameters previously evaluated (Tiselius, World J Urol 1997; 15:176-85). Other methods imply the use of more or less complex instrumentation (Berg et al., Urol Res 2009;37:55-6 ). In fact crystalluria also constitutes a measure of the overall crystallization capacity of urine. Nevertheless when conditions are not extreme, variations in sample handling can greatly affect crystalluria test results and errors and irreproducibility may result.
The proposed test permits the easy identification of the clearly altered urine, i.e. the urines that undoubtedly have an important implication on calculus development due to their high crystallization risk. This test evaluates the overall crystallization risk of urine through a very simple procedure using 30 mL of fresh urine. Urine was considered lithogenic when at least one of the four conditions summarized in Table I was present. These biochemical findings corresponded to previous studies that demonstrated that practically 100% of urine meeting such conditions belonged to stone-formers (Galan et al., Urol Int 1996;56:79-85 and Grases et al., Clin Chim Acta 1997; 263:43-55). Thus positive test values were clearly associated with urines that have been considered as lithogenic. Interestingly, a majority of bilateral stone-formers exhibited urines whose biochemical parameters fell within the criteria for lithogenic urine.
The test will be especially useful for fast, low-cost screening of urine of calcium stone-formers and to detect individuals whose urine is clearly altered; such patients should be scheduled for ulterior complete urine analysis, since this test evaluates the global crystallization capacity of urine without evaluation of individual parameters (calciuria, oxaluria, phosphaturia, etc.). Also, the test will be useful to identify any tendency toward development of calcium calculi in individuals at high lithogenic risk, to detect periods of high lithogenic activity, and also to evaluate the efficacy of therapy chosen to reduce the levels of urinary lithogenic factors.
| (1) | [Calcium] | > 270 mg/L |
| (2) | [Oxalate] | > 40 mg/L |
| (3) | [Calcium]/[Citrate] ratio | > 0.33 and [Calcium] > 170 mg/L |
| (4) | Three or more simultaneously altered urinary lithogenic risk parameters: | |
| pH | < 5.5 | |
| pH | > 6.0 | |
| [Calcium] | > 170 mg/L | |
| [Phosphorus] | > 1000 mg/L | |
| [Urate] | > 600 mg/L | |
| [Citrate] | < 230 mg/L | |
| [Oxalate] | > 30 mg/L |
Written by:
Félix Grases, Antonia Costa-Bauzá, and Rafel M. Prietoas as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
Urinary lithogenesis risk tests: Comparison of a commercial kit and a laboratory prototype test - Abstract
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