Urine is a saturated equilibrium and not a metastable supersaturated solution: evidence from crystalluria and the general composition of calcium salt and uric acid calculi

LITHOSCREEN: a comprehensive screening program and database for the assessment and treatment management of patients with kidney stones

The aim of the LITHOSCREEN project was to construct a comprehensive screening program and database for recording and assessing the various risk factors for stone-formation in patients with urolithiasis. It is intended for use in Stone Clinics and is now being made available free of charge to researchers in the field who wish to maintain a comprehensive record of their patients' medical histories, demographic backgrounds, lifestyle activities, metabolic abnormalities, biochemical risk of forming stones of various types, diet histories, stone analysis and long-term treatment records. From the recorded data for each patient, the program automatically calculates numerous functions important in the understanding of the clinical and chemical risk factors for stone-formation, including the renal handling of the ions involved, various metabolic functions, the biochemical risk of forming kidney stones (P_SF), the Tiselius Indices of the supersaturation of urine with respect to calcium oxalate and calcium phosphate, the projected effects of changing the composition of each patient's urinary composition on the risk of stone recurrence, and a program for analysing the diet of patients. It automatically produces one-page Summaries of each patient's biochemical and dietary records with abnormal values highlighted according to a "traffic-light" colour-coding system and generates charts designed to improve patient compliance with treatment in the form of colour-coded "Target Diagrams" showing (a) the patient's 24-h urine composition, (b) the patient's biochemical risk of forming stones of different types and (c) the composition of the patient's diet. The Summary pages and "Target Diagrams" are suitable for inclusion in the patient's Case Notes. LITHOSCREEN also produces charts projecting the effect of changing the composition of urine on the patient's biochemical risk of forming further stones. These graphs provide clues as to which urinary risk factors to target to reduce the patient's risk of stone recurrence.

Structural Biology of Calcium Phosphate Nanoclusters Sequestered by Phosphoproteins

Biofluids that contain stable calcium phosphate nanoclusters sequestered by phosphopeptides make it possible for soft and hard tissues to co-exist in the same organism with relative ease. The stability diagram of a solution of nanocluster complexes shows how the minimum concentration of phosphopeptide needed for stability increases with pH. In the stable region, amorphous calcium phosphate cannot precipitate. Nevertheless, if the solution is brought into contact with hydroxyapatite, the crystalline phase will grow at the expense of the nanocluster complexes. The physico-chemical principles governing the formation, composition, size, structure, and stability of the complexes are described. Examples are given of complexes formed by casein, osteopontin, and recombinant phosphopeptides. Application of these principles and properties to blood serum, milk, urine, and resting saliva is described to show that under physiological conditions they are in the stable region of their stability diagram and so cannot cause soft tissue calcification. Stimulated saliva, however, is in the metastable region, consistent with its role in tooth remineralization. Destabilization of biofluids, with consequential ill-effects, can occur when there is a failure of homeostasis, such as an increase in pH without a balancing increase in the concentration of sequestering phosphopeptides.

Urinary saturation: casual or causal risk factor in urolithiasis?

OBJECTIVE

To assess (i) the extent to which urinary supersaturation (SS) has successfully discriminated between stone formers and healthy individuals (N), (ii) whether absolute SS has diagnostic worth and (iii) whether high SS is the fundamental cause of stone formation per se.

MATERIALS AND METHODS

Google Scholar was used to identify studies in which urinary compositional data had been determined. In those cases where SS values were not given, or where other risk indices had been reported, they were (re-)calculated. Collected data were termed 'global' but were then 'filtered' according to stone type and protocols used for SS calculations. SS distribution plots for calcium oxalate, brushite and uric acid were constructed. Data were statistically analysed using the unpaired t-test and Mann-Whitney test.

RESULTS

In all, 47 studies yielded 123 SS values for healthy individuals and 122 values for stone formers. The mean and median SS values were significantly greater in stone formers compared with healthy individuals in all but one of the comparisons. Wide variations in SS occurred for healthy individuals and stone formers. The two groups could not be separated.

CONCLUSIONS

Absolute SS has no diagnostic worth. It is impossible to quantify the meaning of a 'high' SS value. Urines cannot be identified as originating from healthy individuals or stone formers based on their SS. SS should be determined in clinical and research settings for relative comparisons during the assessment of treatment efficacies. This study provides a compelling argument for SS being a casual factor rather than a causal one.

Methods for diagnosing the risk factors of stone formation

OBJECTIVE

To compare various systems for assessing the risk of recurrent stones, based on the composition of urine.

METHODS

The relative supersaturation (RSS) of urine, the Tiselius Indices, the Robertson Risk Factor Algorithms (RRFA) and the BONN-Risk Index were compared in terms of the numbers of variables required to be measured, the ease of use of the system and the value of the information obtained.

RESULTS

The RSS methods require up to 14 analyses in every urine sample but measure the RSS of all the main constituents of kidney stones. The Tiselius Indices and the RRFA require only seven analyses. The Tiselius Indices yield information on the crystallisation potentials (CP) of calcium oxalate and calcium phosphate; the RRFA also provide information on the CP of uric acid. Both methods provide details on the particular urinary abnormalities that lead to the abnormal CP of that urine. The BONN-Risk Index requires two measurements in each urine sample but only provides information on the CP of calcium oxalate. Additional measurements in urine have to be made to identify the cause of any abnormality.

CONCLUSIONS

The methods that are based on measuring RSS are work-intensive and unsuitable for the routine screening of patients. The Tiselius Indices and the RRFA are equally good at predicting the risk of a patient forming further stones. The BONN-Risk Index provides no additional information about the causative factors for any abnormality detected.

Estimating the precipitation potential in urine-collecting systems

Precipitation in urine-separating toilets (NoMix toilets) and waterless urinals causes severe maintenance problems and can strongly reduce the content of soluble phosphate. In this study, we present a computer model for estimating the precipitation potential (PP) in urine-collecting systems. Calculating the PP enables to predict the composition and mass concentration of precipitates. We used our computer model for investigating how urea hydrolysis and dilution with flushing water affect precipitation. In a previous study, we found that microbial urea hydrolysis (ureolysis) triggers precipitation and that the amount of precipitates is limited by calcium and magnesium. With the present simulations, we could confirm these findings. We determined that only a small fraction of urea has to be hydrolysed for reaching 95% of the maximum PP. Since urease-positive bacteria are abundant in urine-collecting systems, strong precipitation is very likely. In further simulations, we determined that struvite (MgNH(4)PO(4).6H(2)O) and hydroxyapatite (HAP, Ca(10)(PO(4))(6)(OH)(2)) are the main precipitate compounds. If urine is highly diluted with tapwater, calcite (CaCO(3)) occurs as well. HAP is the only calcium phosphate mineral, although several others were supersaturated. Additionally, the simulations indicated that urine dilution diminishes the risk of blockages, since the mass concentration of precipitates decreases with the volume of flushing water. Rainwater flushing is more effective than flushing with tapwater. Moreover, flushing with tapwater leads to high phosphate fixation, because the total amount of calcium and magnesium ions increases, while the total amount of phosphate keeps constant. Finally, we compared simulation results with field measurements and found good agreement at low and very high urine dilution.

[Effects of water diuresis on the urinary ph of patients under relapsing lithiasis]

INTRODUCTION

It has been observed that in healthy individuals the increase in urinary flow induced by water overload may be enough to alter the urinary Ph to obtain values considered safe in the prophylaxis of lithogenesis. The aim of the present paper is to determine the effects of water diuresis on the urinary Ph of patients suffering from relapsing lithiasis.

MATERIAL AND METHOD

26 patients were included in the present study. The urinary Ph of all patients was measured along two consecutive days, at 8.30 and again at 12.30, under normal conditions (the first day) and once they had received a water load equivalent to 1.5% of their weight (the second day).

RESULTS

The altered mean value of the Ph induced on the first day by the circadian rhythm showed a mean of 0.13 units of Ph, which lacks statistical significance (p > 0.05). However, on the second day we obtained a value of 0.42, which is statistically significant (p < 0.01). The normal tendency after the water overload was towards a positive increase of the Ph in those patients whose urine showed a preload Ph value < 6.1, whereas those individuals with a preload Ph value > 6.48 suffered negative increases.

CONCLUSIONS

The increase of diuresis induced by water load proved enough to provoke an increase of urinary Ph when its baseline value is < 6.1, or either a decrease when its baseline value is > 6.48. In both cases, Ph values ranged between 6-6.5 which are considered safe values in the prophylaxis of lithogenesis. The more separated the baseline urinary Ph is from the 6.1-6.48 range, the greater the effect of the water load.

Comparison of urine composition of healthy Labrador retrievers and miniature schnauzers

OBJECTIVE

To compare urine composition in Labrador Retrievers (LR) and Miniature Schnauzers (MS) fed the same dog food.

ANIMALS

8 healthy LR (mean [+/- SD] age, 3.1+/-1.7 years) and 8 healthy MS (mean age, 3.7+/-1.3 years).

PROCEDURE

A nutritionally complete dry dog food was fed to the dogs for 24 days. Urinary pH, volume, specific gravity, frequency of urination, and urinary concentrations of 12 analytes were measured for each dog; urinary relative supersaturation (RSS) with calcium oxalate and brushite (calcium hydrogen phosphate dihydrate) were calculated from these values.

RESULTS

MS urinated significantly less often and had a lower urine volume (ml/kg of body weight per d) and a significantly higher urine pH, compared with LR. Urinary calcium concentration and brushite RSS were significantly higher in the urine of MS. As a result of a high calorie requirement, primarily as a result of high surface area to volume ratio, MS had significantly higher intake (per kg body weight) of dietary minerals, compared with LR.

CONCLUSIONS AND CLINICAL RELEVANCE

Differences in urine composition exist between breeds fed the same diet, some of which, including lower urine volume, higher calcium concentration, and higher brushite RSS, may contribute to the high prevalence of calcium oxalate uroliths observed in MS. Differences between breeds should be considered when evaluating strategies for controlling calcium oxalate stone formation.