Critical Reappraisal of Methods for Measuring Urine Saturation with Calcium Salts

Background: Metabolic and physicochemical evaluation is recommended to manage the condition of patients with nephrolithiasis. The estimation of the saturation state (β values) is often included in the diagnostic work-up, and it is preferably performed through calculations. The free concentrations of constituent ions are estimated by considering the main ionic soluble complexes. It is contended that this approach is liable to an overestimation of β values because some complexes may be overlooked. A recent report found that β values could be significantly lowered upon the addition of new and so far neglected complexes, [Ca(PO₄)Cit]^4- and [Ca₂H₂(PO₄)₂]. The aim of this work was to assess whether these complexes can be relevant to explaining the chemistry of urine. Methods: The Ca-phosphate-citrate aqueous system was investigated by potentiometric titrations. The stability constants of the parent binary complexes [Cacit]^- and [CaPO₄]^-, and the coordination tendency of PO₄^3- toward [Ca(cit)]^- to form the ternary complex, were estimated. β_CaOx and β_CaHPO4 were then calculated on 5 natural urines by chemical models, including or not including the [CaPO₄]^- and [Ca(PO₄)cit]^4- species. Results: Species distribution diagrams show that the [Ca(PO₄)cit]^4- species was only noticeable at pH > 8.5 and below 10% of the total calcium. β values estimated on natural urine were slightly lowered by the formation of [CaPO₄]^- species, whereas [Ca(PO₄)cit]^4- results were irrelevant. Conclusions: While [CaPO₄]^- species have an impact on saturation levels at higher pHs, the existence of ternary complex and of the dimer is rejected.

Sex Differences of Kidney Stone Urine Risk Factors after Roux-en-Y Gastric Bypass

INTRODUCTION

Roux-en-Y gastric bypass (RYGB) is a bariatric surgical procedure that is associated with higher risk of kidney stones after surgery. We examined urine composition in 18 men and women before and after RYGB to examine differences in kidney stone risk.

METHODS

Three 24-h urine collections were performed before and 1 year after RYGB. We analyzed mean urinary values for pre- and post-RYGB collections and compared men and women.

RESULTS

Seven men and eleven women completed pre- and post-RYGB urine collections. Pre-RYGB, men had higher calcium oxalate supersaturation (CaOx SS) (7.0 vs. 5.0, p = 0.04) compared with women. Post-RYGB, women had higher urine CaOx SS (13.1 vs. 4.6, p = 0.002), calcium phosphate supersaturation (1.04 vs. 0.59, p = 0.05), and lower urine volumes (1.7 vs. 2.7L, p < 0.001) compared with men.

DISCUSSION/CONCLUSION

There are important differences in urine composition by sex that may contribute to higher kidney stone risk in women after RYGB compared with men.

[Metabolic effects of Cholecalciferol supplementation in kidney stone formers with vitamin D deficiency]

INTRODUCTION

In this paper we investigated whether cholecalciferol supplementation, prescribed to treat vitamin D deficiency in patients with nephrolithiasis, increased the risk of stone recurrence.

METHODS

Calcium excretion and urine supersaturation with calcium oxalate (βCaOx) and brushite (βbsh) were evaluated in 33 kidney stone formers (aged 56±17; 12 males), both before and after therapy with cholecalciferol, prescribed as oral bolus of 100.000-200.000 UI, followed by maintenance doses, repeated every week (5.000-10.000 UI) or month (25.000-50.000 UI). During the study, patients followed a dietary regimen which included a daily calcium intake of about 800-1000 mg.

RESULTS

Urinary nitrogen, sodium and ash-acid excretion did not significantly change during the study. After cholecalciferol supplementation, the main results were as follows: both serum calcium and phosphate did not vary significantly; 25(OH)VitD₃ increased from 11,8±5,5 to 40,2±12,2 ng/mL (p<0,01); 1,25(OH) ₂ VitD₃ increased from 41,6±17,6 to 54,0±16,0 pg/mL (p<0,01); PTH decreased from 75,0±27,2 to 56,7±21,1 pg/mL (p<0,01); daily urinary calcium increased from 2,7±1,5 to 3,6±1,6 mg/Kg b.w. (p<0,01), whereas fasting urinary calcium did not change significantly. After therapy, βbsh increased from 0,9±0,7 to 1,3±1,3 (p=0,02) and βCaOx did not vary significantly. Before cholecalciferol supplementation, 6/33 patients (18.2%) were hypercalciuric, whereas 13/33 patients (39,4%) showed hypercalciuria after supplementation (pX²=0,03).

CONCLUSIONS

Cholecalciferol supplementation for vitamin D deficiency may increase both urinary calcium and urine supersaturation in stone formers. If vitamin D supplements are needed in these patients, a careful monitoring of urine metabolic profile is warranted, in order to customize the metaphylaxis accordingly (hydration, potassium citrate, thiazides).

Impact of Potassium Citrate vs Citric Acid on Urinary Stone Risk in Calcium Phosphate Stone Formers

PURPOSE

To our knowledge no medication has been shown to be effective for preventing recurrent calcium phosphate urinary stones. Potassium citrate may protect against calcium phosphate stones by enhancing urine citrate excretion and lowering urine calcium but it raises urine pH, which increases calcium phosphate saturation and may negate the beneficial effects. Citric acid can potentially raise urine citrate but not pH and, thus, it may be a useful countermeasure against calcium phosphate stones. We assessed whether these 2 agents could significantly alter urine composition and reduce calcium phosphate saturation.

MATERIALS AND METHODS

In a crossover metabolic study 13 recurrent calcium phosphate stone formers without hypercalciuria were evaluated at the end of 3, 1-week study phases during which they consumed a fixed metabolic diet and received assigned study medications, including citric acid 30 mEq twice daily, potassium citrate 20 mEq twice daily or matching placebo. We collected 24-hour urine specimens to perform urine chemistry studies and calculate calcium phosphate saturation indexes.

RESULTS

Urine parameters did not significantly differ between the citric acid and placebo phases. Potassium citrate significantly increased urine pH, potassium and citrate compared to citric acid and placebo (p <0.01) with a trend toward lower urine calcium (p = 0.062). Brushite saturation was increased by potassium citrate when calculated by the relative supersaturation ratio but not by the saturation index.

CONCLUSIONS

Citric acid at a dose of 60 mEq per day did not significantly alter urine composition in calcium phosphate stone formers. The long-term impact of potassium citrate on calcium phosphate stone recurrence needs to be studied further.

Association of Body Mass Index, Waist Circumference, and Waist-Stature Ratio With Urine Composition in Patients With Urolithiasis

INTRODUCTION

This study was aimed to evaluate the correlation of body mass index (BMI), waist circumference (WC), and waist-stature ratio (WSR) with urinary composition in urolithiasis patients.

MATERIALS AND METHODS

Medical reports of 1410 urolithiasis patients referred to a tertiary in Tehran, from 2010 to 2015, were reviewed. Collected data included WC, BMI, and WSR, 24-hour urine composition, and the first-morning urine pH. Urinary relative supersaturation of calcium oxalate, calcium phosphate, and uric acid were calculated. Linear correlation and logistic regression models were used for study analyses.

RESULTS

A total of 511 records were reviewed. In the women, supersaturation of calcium oxalate significantly correlated with BMI, WC, and WSR. Supersaturation of uric acid significantly correlated with WC. Using regression analyses, BMI and WSR were associated with greater supersaturation of calcium oxalate abnormality, which persisted after adjustment for confounding factors (odds ratio, 1.080; 95% confidence interval, 1.001 to 1.166 for BMI; odds ratio, 1.053; 95% confidence interval, 1.001 to 1.108 for WSR). Larger WC accompanied abnormal values for supersaturation of calcium oxalate; however, the model was marginally significant (odds ratio, 1.032; 95% confidence interval, 1.000 to 1.065; P = .05) in multivariable analysis. In the men on the other hand, none of the obesity indexes were associated with the supersaturation measures.

CONCLUSIONS

Although both obesity and abdominal obesity correlated with supersaturation of calcium oxalate, mostly by changes in urine volume and pH in women, none of those indexes showed significant correlation with urine composition in the men population of our study.

Fourier Transform Infrared Analysis of Urinary Calculi and Metabolic Studies in a Group of Sicilian Children

INTRODUCTION

Prevalence of urinary calculi in children has been increasing in the past years. We performed an analysis of the chemical composition of stones formers of the pediatric population in our geographical area over the years 2005 to 2013.

MATERIALS AND METHODS

Fourier transform infrared spectroscopy was employed for the determination of the calculus composition of a group of Sicilian children, and metabolic studies were performed to formulate the correct diagnosis and establish therapy.

RESULTS

The prevalence of stone formation was much higher for boys than for girls, with a sex ratio of 1.9:1. The single most frequent component was found to be calcium oxalate monohydrate, and calcium oxalates (pure or mixed calculi) were the overall most frequent components. Calcium phosphates ranked 2nd for frequency, most often in mixed calculi, while urates ranked 3rd. The metabolic disorder most often associated with pure calcium oxalate monohydrate calculi was hypocitraturia, while hyperoxaluria was predominantly associated with calcium oxalate dihydrate calculi.

CONCLUSIONS

Mixed calculi had the highest prevalence in our pediatric population. Our data showed that Fourier transform infrared spectroscopy was a useful tool for the determination of the calculi composition.

Crystalluria

Crystalluria is a marker of urine supersaturation with substances deriving from metabolic disorders, inherited diseases or drugs. The investigation of crystalluria must be done according to a protocol which includes the delivery to the laboratory of a proper urine sample, the use of a microscope equipped with polarized light, the accurate knowledge of urine pH, and a comprehensive examination of the crystals, which is based on their identification, quantification and size measurement. For unusual crystals, infrared spectroscopy may also be needed. The main urinary crystalline categories include: calcium oxalates, calcium phosphates, uric acids and urates, struvite, aminoacids (cystine), purines (2,8-dihydroxyadenine and xanthine) and drugs (e.g. sulfamethoxazole, amoxycillin, ceftriaxone, atazanavir). The investigation of crystalluria is a cheap and valuable tool for the detection and the monitoring of inherited and acquired diseases associated with urinary stone formation or renal function impairment - either acute or chronic - due to intrarenal crystal precipitation.

Impact of Increasing Dietary Calcium Levels on Calcium Excretion and Vitamin D Metabolites in the Blood of Healthy Adult Cats

Background

Dietary calcium (Ca) concentrations might affect regulatory pathways within the Ca and vitamin D metabolism and consequently excretory mechanisms. Considering large variations in Ca concentrations of feline diets, the physiological impact on Ca homeostasis has not been evaluated to date. In the present study, diets with increasing concentrations of dicalcium phosphate were offered to ten healthy adult cats (Ca/phosphorus (P): 6.23/6.02, 7.77/7.56, 15.0/12.7, 19.0/17.3, 22.2/19.9, 24.3/21.6 g/kg dry matter). Each feeding period was divided into a 10-day adaptation and an 8-day sampling period in order to collect urine and faeces. On the last day of each feeding period, blood samples were taken.

Results

Urinary Ca concentrations remained unaffected, but faecal Ca concentrations increased (P < 0.001) with increasing dietary Ca levels. No effect on whole and intact parathyroid hormone levels, fibroblast growth factor 23 and calcitriol concentrations in the blood of the cats were observed. However, the calcitriol precursors 25(OH)D₂ and 25(OH)D₃, which are considered the most useful indicators for the vitamin D status, decreased with higher dietary Ca levels (P = 0.013 and P = 0.033). Increasing dietary levels of dicalcium phosphate revealed an acidifying effect on urinary fasting pH (6.02) and postprandial pH (6.01) (P < 0.001), possibly mediated by an increase of urinary phosphorus (P) concentrations (P < 0.001).

Conclusions

In conclusion, calcitriol precursors were linearly affected by increasing dietary Ca concentrations. The increase in faecal Ca excretion indicates that Ca homeostasis of cats is mainly regulated in the intestine and not by the kidneys. Long-term studies should investigate the physiological relevance of the acidifying effect observed when feeding diets high in Ca and P.

Short-Term Tolvaptan Increases Water Intake and Effectively Decreases Urinary Calcium Oxalate, Calcium Phosphate and Uric Acid Supersaturations

PURPOSE

Some patients cannot effectively increase water intake and urine volume to prevent urinary stones. Tolvaptan, a V2 receptor antagonist, blocks water reabsorption in the collecting duct and should decrease urinary supersaturation of stone forming solutes, although this action has never been proved.

MATERIALS AND METHODS

We conducted a double-blind, randomized, placebo controlled, crossover study of 21 calcium urinary stone formers stratified into majority calcium oxalate (10 patients) and calcium phosphate (11) groups. Patients received 45 mg tolvaptan per day or placebo for 1 week, followed by a washout week and crossover to tolvaptan or placebo for week 3. A 24-hour urine sample was collected at the end of weeks 1 and 3.

RESULTS

Tolvaptan vs placebo decreased urinary osmolality (mean ± SD 204 ± 96 vs 529 ± 213 mOsm/kg, p <0.001) and increased urinary volume (4.8 ± 2.9 vs 1.8 ± 0.9 L, p <0.001). The majority of urinary solute excretion rates, including sodium and calcium, did not change significantly, although oxalate secretion increased slightly (from mean ± SD 15 ± 8 to 23 ± 8 mg per 24 hours, p = 0.009). Mean ± SD urinary calcium oxalate supersaturation (-0.01 ± 1.14 vs 0.95 ± 0.87 dG, p <0.001), calcium phosphate supersaturation (-1.66 ± 1.17 vs -0.13 ± 1.02 dG, p <0.001) and uric acid supersaturation (-2.05 ± 4.05 vs -5.24 ± 3.12 dG, p = 0.04) all dramatically decreased. Effects did not differ between the calcium oxalate and calcium phosphate groups (p >0.05 for all interactions).

CONCLUSIONS

Tolvaptan increases urine volume and decreases urinary supersaturation in calcium stone formers. Further study is needed to determine if long-term use of V2 receptor antagonists results in fewer stone events.

Mechanism by which shock wave lithotripsy can promote formation of human calcium phosphate stones

Human stone calcium phosphate (CaP) content correlates with higher urine CaP supersaturation (SS) and urine pH as well as with the number of shock wave lithotripsy (SWL) treatments. SWL does damage medullary collecting ducts and vasa recta, sites for urine pH regulation. We tested the hypothesis that SWL raises urine pH and therefore Cap SS, resulting in CaP nucleation and tubular plugging. The left kidney (T) of nine farm pigs was treated with SWL, and metabolic studies were performed using bilateral ureteral catheters for up to 70 days post-SWL. Some animals were given an NH4Cl load to sort out effects on urine pH of CD injury vs. increased HCO3 (-) delivery. Histopathological studies were performed at the end of the functional studies. The mean pH of the T kidneys exceeded that of the control (C) kidneys by 0.18 units in 14 experiments on 9 pigs. Increased HCO3 (-) delivery to CD is at least partly responsible for the pH difference because NH4Cl acidosis abolished it. The T kidneys excreted more Na, K, HCO3 (-), water, Ca, Mg, and Cl than C kidneys. A single nephron site that could produce losses of all of these is the thick ascending limb. Extensive injury was noted in medullary thick ascending limbs and collecting ducts. Linear bands showing nephron loss and fibrosis were found in the cortex and extended into the medulla. Thus SWL produces tubule cell injury easily observed histopathologically that leads to functional disturbances across a wide range of electrolyte metabolism including higher than control urine pH.

Nanouric acid or nanocalcium phosphate as central nidus to induce calcium oxalate stone formation: a high-resolution transmission electron microscopy study on urinary nanocrystallites

PURPOSE

This study aimed to accurately analyze the relationship between calcium oxalate (CaOx) stone formation and the components of urinary nanocrystallites.

METHOD

High-resolution transmission electron microscopy (HRTEM), selected area electron diffraction, fast Fourier transformation of HRTEM, and energy dispersive X-ray spectroscopy were performed to analyze the components of these nanocrystallites.

RESULTS

The main components of CaOx stones are calcium oxalate monohydrate and a small amount of dehydrate, while those of urinary nanocrystallites are calcium oxalate monohydrate, uric acid, and calcium phosphate. The mechanism of formation of CaOx stones was discussed based on the components of urinary nanocrystallites.

CONCLUSION

The formation of CaOx stones is closely related both to the properties of urinary nanocrystallites and to the urinary components. The combination of HRTEM, fast Fourier transformation, selected area electron diffraction, and energy dispersive X-ray spectroscopy could be accurately performed to analyze the components of single urinary nanocrystallites. This result provides evidence for nanouric acid and/or nanocalcium phosphate crystallites as the central nidus to induce CaOx stone formation.

A proposed method for approximate estimates of the ion-activity products of calcium oxalate and calcium phosphate in spot-urine samples or in urine samples collected during less well defined periods of time

The purpose of this study is to derive approximate estimates of ion-activity products of CaOx (APCaOx) and CaP (APCaP) useful for spot urine or other less well defined short-term urine collections. In accordance with previously applied and described principles for estimating ion-activity products, the intention was to derive simplified estimates of AP(CaOx)CONC and AP(CaP)CONC by using urine concentrations of the most important determinants of APCaOx and APCaP. A comparison thus was made between estimates derived in that manner and AP(CaOx) index and AP(CaP) index obtained from calculations based on analysis of 24 h urine samples. The best fit between estimates of AP(CaOx) index in 24 h urine and AP(CaOx) indexCONC was obtained with the following formula (r = 0.99; p = 0.0000): [Formula in text] The corresponding formula for AP (CaP) indexCONC was derived from comparison with the corresponding calculations of AP(CaP) index in 24 h urine (r = 0.91; p = 0.0000): [Formula in text] The proposed simplified formulas enable calculation of approximate estimates of APCaOx and APCaP in spot-urine samples or any kind of urine collection for which duration of the collection period is less well known and by using the concentrations (c) of the variables in mmol/L in the two formulas.

Effect of Ramadan fasting on urinary risk factors for calculus formation

INTRODUCTION

Even though dehydration could aggravate formation of urinary calculi, the effects of fluid and food restriction on calculus formation is not thoroughly defined. The purpose of this study is to evaluate the effects of fluid and food restriction in Ramadan fasting on urinary factors in kidney and urinary calculus formation.

MATERIALS AND METHODS

Fifty-seven men aged 30 to 55 years old, including 37 recurrent calcium calculus formers and 20 with no history of kidney calculi were evaluated for blood tests, ultrasonography investigations, urinalysis, urine culture, and also 24-hour urine collection test. Metabolites including calcium, oxalate, citrate, uric acid, magnesium, phosphate, potassium, sodium, and creatinine were measured before and during Ramadan fasting. The values of calculus-precipitating solutes as well as inhibitory factors were documented thoroughly.

RESULTS

Total excretion of calcium, phosphate, and magnesium in 24-hour urine and also urine volume during fasting were significantly lower than those in the nonfasting period. Urine concentration of calcium during fasting was significantly lower than nonfasting (P < .001). Urine concentrations of uric acid, citrate, phosphate, sodium, and potassium during fasting were significantly higher than nonfasting. Uric acid supersaturation was accentuated, and calcium phosphate supersaturation was decreased significantly during fasting. There was no significant increase in calcium oxalate supersaturation during the fasting period.

CONCLUSIONS

Fasting during Ramadan has different effects on total excretion and concentrations of urinary precipitate and inhibitory factors contributing to calculus formation. We did not find enough evidence in favor of increased risks of calculus formation during Ramadan fasting.

[State of bone structures in children with acute leukemia, experiencing unfavorable factors from Chernobyl accident]

The authors present an assessment of bone structure condition in children with acute leukemia. The changes in the collagen molecule, amino acid composition of urine and proteins reparation processes were revealed. Calcium phosphate excretion in the patients urine were increased. The serum osteocalcin level and colony formation efficiency of bone marrow fibroblasts in acute leukemia patients are lower than in control group. In the initial period of the disease 32% of patients have disturbancies in their endocrine status. The bone structure violation is combined with unfavorable disease outcome. The effectiveness of the treatment and prevention steps in acute leukemia patients depends on the leukemic process stage.

The most important metabolic risk factors in recurrent urinary stone formers

PURPOSE

To evaluate different urinary factors contributing to idiopathic calcium stone disease for determining appropriate medical treatments.

MATERIALS AND METHODS

Two 24-hour urine samples were collected from 106 male recurrent idiopathic calcium stone formers and another 109 randomly selected men as the control group matching for age.

RESULTS

Cases had significantly higher mean urine oxalate, calcium, uric acid, and chloride in comparison with the healthy controls (P < .001). After necessary adjustment, only mean urine levels of oxalate and uric acid were higher in stone formers than those in controls. The mean value of supersaturation for calcium oxalate was significantly higher in patients than the controls (P = .001); whereas supersaturation for calcium phosphate and uric acid did not reach statistical significance (P = .675 and P = .675, respectively). Hyperoxaluria and hypercalciuria were among the most frequent abnormalities. After categorizing urine parameter values into four quartiles, the risk of stone formation was found to increase as the urine calcium, oxalate, uric acid, chloride, and citrate rise. In contrast, the risk of stone formation decreased with the increase of urine potassium.

CONCLUSION

Oxalate seems to play the most important role as urinary stone risk factor in our population followed by calcium and uric acid. In addition to the risk factors, it seems that supersaturation as the sum of all risk factors probably has a high predictive value.

Mutation analysis and serum FGF23 level in a patient with pulmonary alveolar microlithiasis

Pulmonary alveolar microlithiasis (PAM) is a rare, hereditary disorder characterized by ectopic formation of calcium-phosphate microliths in the alveolar space. PAM has been reported to arise from inactivating mutations in SLC34A2, encoding a sodium-dependent phosphate co-transporter essential for phosphate transport in the lungs and small intestine. Serum levels of the phosphaturic hormone fibroblast growth factor-23 (FGF23) in PAM have not been determined. Our objectives were to investigate the genetic etiology and circulating level of FGF23 in a 50-year-old male with clinical characteristics of PAM and extra-pulmonary calcifications. The SLC34A2 and FGF23 genes were sequenced for mutations and serum FGF23 analyzed by ELISA. We found no disease-causing mutations or single nucleotide polymorphisms in the genes investigated. Importantly, repeated measurements revealed undetectable or markedly low serum FGF23 (<3-11 RU/ml). Surprisingly, in the face of low serum FGF23, 1,25-dihydroxy vitamin D₃ level was low-normal and parathyroid hormone mildly elevated. Total 24-h urinary excretion of phosphate and calcium were low, as was fractional urinary excretion of calcium. In contrast, fractional excretion of phosphate was above normal, likely due to elevated PTH. Collectively, PAM may be a polygenic disorder that arises from mutations other than in SLC34A2. The low FGF23 level in our PAM patient supports an intestinal-bone axis, leading to decreased FGF23 expression when intestinal phosphate absorption is compromised.

Phosphate balance in phosphate supplemented and unsupplemented health subjects during and after hypokinesia

OBJECTIVE

To demonstrate the effect of hypokinesia (HK) and post-HK on phosphate (Pi) imbalance and use of Pi with different Pi imbalance and different Pi consumption: were measured Pi balance, plasma Pi level and Pi loss during HK.

METHODS

Experiments were conducted during the pre-experimental period of 30 days, and the HK period of 364-days and post-HK period of 30-days. Forty healthy male volunteers 24.2 +/- 2.0 yr, were divided into four groups: unsupplemented active control subjects (UACS), unsupplemented hypokinetic subjects (UHKS), supplemented active control subjects (SACS), and supplemented hypokinetic subjects (SHKS). All SACS and SHKS were supplemented with 0.6 mmol dicalcium-phosphate per kg body weight daily.

RESULTS

During HK, Pi imbalance, serum Pi and calcium (Ca2+) levels, fecal Pi loss, and urine Ca2+ and Pi loss increased (P < 0.05) in SHKS and UHKS compared with pre-experimental values and the values in their respective active controls (SACS and UACS). The measured parameters were changed (P < 0.05) more in SHKS than in UHKS. During the initial 20-days of post-HK, serum Pi and Ca2+ levels, fecal P loss, and urine Pi and Ca2+ losses decreased (P < 0.05), while Pi imbalance remained (P < 0.05) depressed in SHKS and UHKS compared with UACS and SACS. The measured parameters were changed (P < 0.05) more in SHKS than in UHKS.

CONCLUSION

The greater Pi imbalance with than without Pi supplementation shows that the risk of higher Pi imbalance is directly related to the magnitude of Pi intake. The higher Pi loss with higher than lower Pi imbalance shows that the risk of greater Pi loss is directly related to the magnitude of Pi imbalance. It is concluded that Pi imbalance increases more when the Pi consumption is higher and that Pi loss increases more with higher than lower Pi imbalance indicating that during HK Pi imbalance is due to the inability of the body to use Pi but not to the Pi shortage in the diet.

Ethnic differences in relative risk of idiopathic calcium nephrolithiasis in North America

PURPOSE

Data on susceptibility to kidney stone disease are sparse in individuals of nonEuropean ancestry residing in North America. We determined the relative risk of calcium nephrolithiasis among people of different ethnic backgrounds living in the same geographic region.

MATERIALS AND METHODS

Using a cross-sectional design 1,128 consecutive patients with idiopathic calcium nephrolithiasis 18 to 50 years old were recruited from a population based Kidney Stone Center in Toronto. Age and gender adjusted odds ratios and 95% confidence intervals were calculated by logistic regression using the 2001 Canada Census population data.

RESULTS

Compared to Europeans the relative risk of calcium nephrolithiasis was significantly higher in individuals of Arabic (OR 3.8, 2.7-5.2), West Indian (OR 2.5, 1.8-3.4), West Asian (OR 2.4, 1.7-3.4) and Latin American (OR 1.7, 1.2-2.4) origin, and significantly lower in those of East Asian (OR 0.4, 0.3-0.5) and African (OR 0.7, 0.5-0.9) background. Several ethnic groups had kidney stone risk factors that were significantly different from those of the European group including higher urinary uric acid, urea excretion and estimated protein intake, and lower urinary citrate, potassium, magnesium and phosphate excretion. However, none was consistent with the variation in relative risk of stone disease overall.

CONCLUSIONS

The propensity for the development of calcium nephrolithiasis differed markedly among ethnic groups in North America. While environmental factors could not be completely ruled out, this variability may reflect the influence of genetic susceptibility because there was no dominant environmental factor to account for the differences in relative risk of stone disease.

Biochemical characterization of primary hyperparathyroidism with and without kidney stones

The exact metabolic-physiological background for kidney stone formation in primary hyperparathyroidism (PHPT) is unclear. To obtain clarification, this retrospective data analysis was conducted in 131 patients with PHPT who had undergone a detailed ambulatory evaluation on a random diet since 1980. The baseline biochemical presentation of 78 patients with PHPT with stones was compared with that of 53 patients without stones. Compared to those without stones, the stone-forming patients had a more marked hypercalciuria (343 +/- 148 vs. 273 +/- 148 mg/day, P < 0.01). Urinary saturation of calcium oxalate and brushite was significantly higher in stone-formers. Serum PTH and fasting urinary calcium were similar between the two groups, but serum phosphorus was significantly lower in stone-formers. Serum calcitriol (available in some patients) showed a slightly higher mean value in stone-formers but the difference was not significant. The increment in urinary calcium after oral load of 1-g calcium was twofold higher among stone-formers. Radial shaft and L2-L4 bone mineral densities resided within the normal ranges. Stone-formers with PHPT display exaggerated urinary calcium excretion due to intestinal hyperabsorption of calcium, contributing to a greater enhancement of the saturation of stone-forming calcium salts.

Physiology of acid-base balance: links with kidney stone prevention

Two processes permit the urine pH and the medullary interstitial pH to remain in an "ideal range" to minimize the risk of forming kidney stones. First, a medullary shunt for NH(3) maintains the urine pH near 6.0 to minimize uric acid precipitation when distal H(+) secretion is high. Second, excreting dietary alkali excreting alkali as a family of organic anions--including citrate--rather than as bicarbonate maintains the urine pH near 6.0 while urinary citrate chelates ionized calcium, which minimizes CaHPO(4) precipitation. In patients with idiopathic hypercalciuria and recurrent calcium oxalate stones, the initial nidus is a calcium phosphate precipitate on the basolateral membrane of the thin limb of the loop of Henle (Randall's plaque). Formation of this precipitate requires medullary alkalinization; K(+) -depletion and augmented medullary H(+)/K(+) -ATPase may be predisposing factors.

Clinical study on the effect of mineral waters containing bicarbonate on the risk of urinary stone formation in patients with multiple episodes of CaOx-urolithiasis

Investigations in healthy persons have shown that drinking mineral water containing HCO(3) has a positive effect on urine supersaturated with calcium oxalate (SS(CaOx)). The present study evaluates in a common setting whether these effects are also relevant in patients with multiepisodic urinary stone formation. A total of 34 patients with evident multiepisodic CaOx-urolithiasis were included in the study. Patients with hyperparathyroidism, renal tubular acidosis, Wilson's disease, Cushing disease, osteoporosis and malignant diseases were excluded. In a cross-over design and double-blinded the patients received 1.5 l of a mineral water with 2.673 mg HCO(3)/l (test water) or the same amount of water with a low mineral content (98 mg HCO(3)/l) (control water) daily for 3 days. During the study period the patients diet was recorded in a protocol, but not standardised. The main target parameter was SS(CaOx )in 24 h urine. In addition, urinary pH and the most important inhibiting and promoting factors were measured in 24 h urine (Ca, Ox, Mg, Cit). Both waters tested led to a highly significant increase in 24 h urine volume without a difference between each other. In the group, drinking the water containing HCO(3) the urinary pH increased significantly and was within a range relevant for metaphylaxis of calcium oxalate stone formation (x=6.73). This change was highly significant compared to the control group. In addition, significantly increased magnesium and citrate concentration were also observed. Supersaturation with calcium oxalate decreased significantly and to a relevant extent; however, there was no difference between the waters tested. As expected, the risk of uric acid precipitation also decreased significantly under bicarbonate water intake. However, an increase of the risk of calcium phosphate stone formation was observed. It is evident that both waters tested are able to lower significantly and to a relevant extent the risk of urinary stone formation in patients with multiepisodic CaOx-urolithiasis. In addition, the bicarbonate water increases the inhibitory factors citrate and magnesium due to its content of HCO(3) and Mg. Thus, it can be recommended for metaphylaxis of calcium oxalate and uric acid urinary stones.

Computation and modeling of the stone-growth related urinary depletion effect using "depletion V1.0"

PURPOSE

During metabolic evaluation stone patients often present with calculi in the urinary tract or are suffering from high frequent formation of small microliths passing routinely the urinary tract. These concrements are presumably in a state of continuous growth. Consequently, the concentrations of the lithogenic components in the voided urine must decrease. Thus, treatment schemes inevitably fail to focus on the true pathogenic urinary composition. Instead, they focus on underestimated concentrations. This can attain high clinical relevance. In recent publications, we introduced a complex physical approach and provided mathematical equations which can be solved analytically. However, to date, solving the equations with a pocket calculator remains cumbersome.

MATERIALS AND METHODS

Depletion V1.0 was developed to integrate the calculation of the depletion effect into the daily treatment of stone patients. Minimum requirement for Depletion V1.0 is the Java 1.2 platform runtime environment, which is supported on nearly all operation systems including Linux, MacOS X, and Windows. The program can be used directly within a Java-compliant web browser (e.g. Firefox, Mozilla, Internet Explorer) or from the program's storage location. The implemented data base provides stone type relevant parameters. Data input is performed via an easy-to-handle graphical user interface.

RESULTS

Results are given as values and interactive plots; computation and update of plots are performed in real time. Result sheets can be exported to platform-independent EPS-format or printed out directly.

CONCLUSIONS

Depletion V1.0 enables the medical practitioner to obtain an improved interpretation of the stone patient's health status. As input, only one set of easy-to-achieve clinical standard parameters is required. The program will be available from the authors as freeware.

Renal stone risk in a simulated microgravity environment: impact of treadmill exercise with lower body negative pressure

PURPOSE

Prolonged exposure to microgravity during spaceflight causes metabolic changes that increase the risk of renal stone formation. Studies during the Gemini, Apollo, Skylab and Shuttle missions demonstrated alterations in renal function, fluid homeostasis and bone resorption that result in increased urinary supersaturation of calcium oxalate, brushite, sodium urate and uric acid. Developing countermeasures to increased urinary supersaturation is an important priority as the duration of space missions increases.

MATERIALS AND METHODS

A total of 11 sets of identical twins remained on 6-degree head down, tilt bed rest for 30 days to simulate prolonged microgravity. One twin per pair was randomly selected to exercise while supine in a lower body negative pressure chamber 6 days weekly for 40 minutes, followed by 5 minutes of resting lower body negative pressure at 50 mm Hg. The other twin served as a nonexercise control. Pressure in the exercise lower body negative pressure chamber (52 to 63 mm Hg) was adjusted to produce footward forces equivalent to those for upright running on Earth at 1.0 to 1.2 x body weight. Pre-bed rest urinary stone risk profiles were done elsewhere after 5 days of a standardized diet, consisting of 170 mEq sodium, 1,000 mg calcium, 0.8 gm/kg animal protein and 2,500 kcal, and then throughout the bed rest and recovery phases of the protocol.

RESULTS

A significant increase in urinary calcium after just 1 week of bed rest was noted in the nonexercise control group (p = 0.001). However, no such increase was noted in the exercise group. Brushite supersaturation increased significantly from bed rest in each group, although the increase was significantly higher in the nonexercise control group than in the exercise group (p = 0.006). Calcium oxalate supersaturation increased during bed rest in the exercise group (p = 0.004). It trended toward a higher level in the nonexercise control group, although this did not achieve significance (p = 0.055) Mean urine volume +/- SD was significantly higher in the nonexercise control group than in the exercise group at bed rest week 2 and at week 3 (2.01 +/- 0.21 vs 1.63 0.18 l and 2.03 +/- 0.22 vs 1.81 +/- 0.20, respectively). Urinary pH was significantly higher in the nonexercise control group than in the exercise group at week 1 and week 3 (6.62 +/- 0.7 vs 6.49 +/- 0.5 and 6.58 +/- 0.6 vs 6.49 +/- 0.8, respectively, p = 0.01).

CONCLUSIONS

Bed rest significantly alters the urinary environment to favor calculous formation. Lower body negative pressure chamber treadmill exercise offers some protection against increases in stone risk during simulated microgravity, particularly with regard to the risks of hypercalciuria and brushite stone formation. The use of lower body negative pressure to augment aerobic exercise in space may decrease the risk of stone formation in astronauts. Adjunct measures, including aggressive hydration and alkalinization therapy, should be considered.

Effect of cinacalcet on urine calcium excretion and supersaturation in genetic hypercalciuric stone-forming rats

Idiopathic hypercalciuria is the most common metabolic abnormality in patients with nephrolithiasis. Through successive inbreeding, we have developed a strain of rats whose urine calcium (UCa) excretion is approximately 8-10-fold greater than that of control rats and who spontaneously form kidney stones. We have termed these rats genetic hypercalciuric stone-forming (GHS) rats. The physiology of the hypercalciuria in the GHS rats closely parallels that of man. We have recently shown that the GHS rat kidneys have an increased number of receptors for calcium (CaR) compared to Sprague-Dawley rats, the strain of rats originally bred to develop the GHS rats. Calcimimetics, such as cinacalcet (Cin), increase the sensitivity of the CaR to Ca. The effects of Cin on UCa are complex and difficult to predict. We tested the hypothesis that Cin would alter urinary (U) Ca and supersaturation with respect to calcium hydrogen phosphate (CaHPO(4)) and calcium oxalate (CaOx). GHS or control rats were fed a normal Ca diet (0.6% Ca) for 28 days with Cin (30 mg/kg/24 h) added to the diet of half of each group for the last 14 days. The protocol was then repeated while the rats were fed a low Ca (0.02% Ca) diet. We found that Cin led to a marked reduction in circulating parathyroid hormone and a modest reduction in serum Ca. Cin did not alter UCa when the GHS rats were fed the normal Ca diet but lowered UCa when they were fed the low Ca diet. However, Cin did not alter U supersaturation with respect to either CaOx or CaHPO(4) on either diet. If these findings in GHS rats can be confirmed in man, it suggests that Cin would not be an effective agent in the treatment of human idiopathic hypercalciuria and resultant stone formation.

Effect of dietary modification on urinary stone risk factors

BACKGROUND

This study was undertaken to ascertain the effect of dietary modification on urinary stone risks, and to determine whether the response depends on the prevailing urinary calcium.

METHODS

A retrospective data analysis was conducted from our stone registry involving 951 patients with calcareous stones undergoing ambulatory evaluation, whereby 24-hour urine samples were collected during random diet and after dietary modification composed of restriction of calcium, oxalate, sodium, and meat products. Samples were analyzed for stone risk factors. Urinary calcium was also obtained after overnight fast and following a 1 g-calcium load. Changes produced by dietary modification from the random diet were evaluated in 356 patients with moderate-severe hypercalciuria (>6.88 mmol/day, group I), 243 patients with mild hypercalciuria (5.00-6.88 mmol/day, group II), and 352 with normocalciuria (<5.00 mmol/day, group III).

RESULTS

Urinary calcium postcalcium load and the percentage of patients with absorptive hypercalciuria type I were highest in group I, intermediate in group II, and lowest in group III. During dietary modification, urinary calcium declined by 29% in group I, 19% in group II, and 10% in group III. Urinary oxalate did not change. Urinary saturation of calcium oxalate declined by only 12% in group I, 6% in group II, and nonsignificantly in group III, owing to various physicochemical changes in urinary biochemistry, which attenuated the effect of the decline in urinary calcium. Urinary saturation of brushite declined in all 3 groups due to the fall in urinary calcium, phosphorus, and pH. This reduction was more marked in the hypercalciuric groups than in the normocalciuric group. Urinary saturation of monosodium urate also decreased from a decline in urinary sodium and uric acid.

CONCLUSION

Secondary rise in urinary oxalate occurring from calcium restriction can be avoided by concurrent dietary oxalate restriction. Dietary modification (restriction of dietary calcium, oxalate, sodium, and meat products) is more useful in reducing urinary saturation of calcium oxalate among patients with hypercalciuria than among those with normocalciuria.

Factors modulating the pH at which calcium and magnesium phosphates precipitate from human urine

The factors controlling the rate at which crystalline bacterial biofilms develop on indwelling bladder catheters are poorly understood. It is known that normally the pH of voided urine (pHv) is lower than the pH at which calcium and magnesium phosphates come out of urine solution (pHn). In patients who develop infections with urease producing bacteria, however, the pHv rises above the pHn and precipitation of the phosphates occurs in the urine and the biofilm. The aim of this study was to examine ways of manipulating the pHn of urine so that more of its calcium and magnesium remain in solution under alkaline conditions. The experimental data show that pHn can be elevated by decreasing the calcium, magnesium and phosphate concentrations. Increasing the fluid intake of a human subject so that the urinary calcium fell from 120 mg/l to 25 mg/l, for example, resulted in the pHn increasing from 6.48 to 8.22. The addition of citrate to urine also produced a rise in the pHn. The daily consumption of 500 ml of fresh orange juice increased urinary citrate concentrations from 0.35 to around 1.21 mg/ml and the pHn rose from 7.24 to 8.2. The pHn of urine is thus a highly variable parameter. It can be manipulated by controlling the urinary concentrations of magnesium, calcium, phosphate and citrate ions. We suggest that increasing fluid intake with citrate containing drinks would reduce the extent of encrustation on catheters in patients infected with urease producing bacteria.

RESULTS OF A PROSPECTIVE TRIAL TO COMPARE NORMAL URINE SUPERSATURATION IN CHILDREN AND ADULTS

PURPOSE

Urinary stone disease is relatively rare in children but is often due to metabolic abnormalities. Urinary supersaturation (SS) indices have been suggested as more precise predictors of stone recurrence. We previously reported urinary metabolic evaluations in stone-forming children using adult references. We now assess normal SS values in children.

MATERIAL AND METHODS

A prospective trial was performed to assess urinary metabolic profiles in children with no personal or family history of urinary calculi. The 24-hour urine collections were performed and evaluated at an outside central laboratory. Urine chemistries were adjusted for urine creatinine. Urine pH and SS for calcium oxalate, calcium phosphate and uric acid were also assessed. The data were compared to a cohort of normal adults.

RESULTS

A total of 168 samples from 168 adults (58% males) and 51 samples from 30 children (59% males) were evaluated. The mean age of the children was 8.8 years (range 5 to 18). Calcium oxalate SS was similar between children and adults, and urine pH was the major cause of differences seen in the calcium phosphate and uric acid SS indices. Children had a much higher excretion of calcium, oxalate and citrate when adjusted for creatinine.

CONCLUSIONS

There are significant differences in the normal ranges of urine chemistries in children and adults. An understanding of normal supersaturation values may allow metabolic abnormalities in stone-forming children to be more precisely diagnosed and treated.

Thiazides Reduce Brushite, but not Calcium Oxalate, Supersaturation, and Stone Formation in Genetic Hypercalciuric Stone–Forming Rats

Over 59 generations, a strain of rats has been inbred to maximize urine calcium excretion. The rats now excrete eight to 10 times as much calcium as controls. These rats uniformly form calcium phosphate (apatite) kidney stones and have been termed genetic hypercalciuric stone-forming (GHS) rats. The addition of a common amino acid and oxalate precursor, hydroxyproline, to the diet of the GHS rats leads to formation of calcium oxalate (CaOx) kidney stones. Hydroxyproline-supplemented GHS rats were used to test the hypothesis that the thiazide diuretic chlorthalidone would decrease urine calcium excretion, supersaturation, and perhaps stone formation. All GHS rats received a fixed amount of a standard 1.2% calcium diet with 5% trans-4-hydroxy-l-proline (hydroxyproline) so that the rats would exclusively form CaOx stones. Half of the rats had chlorthalidone (Thz; 4 to 5 mg/kg per d) added to their diets. Urine was collected weekly, and at the conclusion of the study, the kidneys, ureters, and bladders were radiographed for the presence of stones. Compared with control, the addition of Thz led to a significant reduction of urine calcium and phosphorus excretion, whereas urine oxalate excretion increased. Supersaturation with respect to the calcium hydrogen phosphate fell, whereas supersaturation with respect to CaOx was unchanged. Rats that were fed Thz had fewer stones. As calcium phosphate seems to be the preferred initial solid phase in patients with CaOx kidney stones, the reduction in supersaturation with respect to the calcium phosphate solid phase may be the mechanism by which thiazides reduce CaOx stone formation.

Clinical implications of abundant calcium phosphate in routinely analyzed kidney stones

BACKGROUND

To better portray the clinical phenotype of kidney stone patients with high calcium phosphate (CaP) stone abundance, we present here clinical and laboratory findings of large numbers of stone formers (SF) with stone CaP ranging from 0% to 100%. Our purpose was to inform clinicians and highlight areas that seem to deserve further research.

METHODS

We calculated average percent CaP (CaP%) in all stones of 1201 patients, and classified them into CaOx (N= 1011) or CaP (N= 190). Sex differences, stone formation rates, urine stone risk factors, extracorporeal shock wave lithotripsy (ESWL) treatments, and relapse during treatment were quantified in relation to stone CaP content.

RESULTS

CaP% has risen for three decades, especially among women. ESWL rates adjusted for numbers of stones and duration of stone disease were higher in CaP SF (0.6 vs. 1.86 and 0.73 vs. 1.82, CaOx vs. CaP, men and women, respectively, P < 0.001), and especially when stones contained brushite (2.90 vs. 1.02 and 3.11 vs. 1.35, brushite vs. not, males and females, respectively, P < 0.001). Urine pH and CaP supersaturation rose in proportion to CaP% in a dose response manner. Relapse rates of CaP and CaOx SF did not differ, and both did well with medical prevention.

CONCLUSION

Stone CaP% has risen for three decades. CaP SF, particularly with brushite stones, receive more ESWL treatments than CaOx SF, not explained by stone number or duration of stone disease. Urine supersaturations explain the high CaP%. High CaP% does not hamper medical stone prevention.

STONE FORMING RISK OF CALCIUM CITRATE SUPPLEMENTATION IN HEALTHY POSTMENOPAUSAL WOMEN

PURPOSE

We evaluated the effect of calcium citrate supplementation alone or in combination with potassium citrate on the stone forming propensity in healthy postmenopausal women.

MATERIALS AND METHODS

A total of 18 postmenopausal women without stones underwent a randomized trial of 4 phases comprised of 2 weeks of treatment with placebo, calcium citrate (400 mg calcium twice daily), potassium citrate (20 mEq twice daily), and calcium citrate and potassium citrate (at same doses). During the last 2 days of each phase urine was collected in 24-hour pools for complete stone risk analysis.

RESULTS

Compared to placebo, calcium citrate increased urinary calcium and citrate but decreased urinary oxalate and phosphate. Urinary saturation of calcium oxalate, brushite and undissociated uric acid did not change. Potassium citrate decreased urinary calcium, and increased urinary citrate and pH. It decreased urinary saturation of calcium oxalate and undissociated uric acid, and did not change the saturation of brushite. When calcium citrate was combined with potassium citrate, urinary calcium remained high, urinary citrate increased even further and urinary oxalate remained reduced from the calcium citrate alone, thereby marginally decreasing the urinary saturation of calcium oxalate. Urinary pH increased, decreasing urinary undissociated uric acid. The increase in pH increased the saturation of brushite despite the decrease in urinary phosphorus.

CONCLUSIONS

Calcium citrate supplementation does not increase the risk of stone formation in healthy postmenopausal women. The co-administered potassium citrate may provide additional protection against formation of uric acid and calcium oxalate stones.

[Clinical value of crystalluria study]

Crystalluria is a marker of urine supersaturation present in both normal and pathological conditions. Indeed, nature and characteristics of the spontaneous crystalluria are of clinical interest for detecting and following biological disorders involved in renal diseases. Method. Crystalluria examination should preferably be performed on first morning urine or fresh fasting voiding samples by polarised microscopy in a Malassez cell. Urine samples must be stored at 37 degrees C or at room temperature and examined within two hours following voiding. Results and discussion. Crystalluria should be interpreted according to various criteria: 1) chemical nature of crystals for abnormal crystals such as struvite, ammonium urate, cystine, dihydroxyadenine, xanthine or drugs; 2) crystalline phase of common chemical species as calcium oxalates, calcium phosphates and uric acids; 3) crystal morphology (calcium oxalates); 4) crystal size (calcium oxalates); 5) crystal abundance (calcium oxalates, calcium phosphates, uric acids, cystine); 6) crystal aggregation (calcium oxalates); 7) frequency of crystalluria assessed on serial first morning urine samples, a very useful tool for long-term surveillance of patients. Within calcium oxalate crystalluria, presence of whewellite is a marker of elevated oxalate concentration (urine oxalate > 0.3 mmol/L); a crystal number > 200/mm 3 is highly suggestive of heavy hyperoxaluria of genetic or absorptive origin. Predominant weddellite crystalluria is most often indicative of an excessive urine calcium concentration (> 3.8 mmol/L); a dodecahedric aspect of the crystals is a marker for heavy hypercalciuria (> 6 mmol/L) while an increased crystal size (>or= 35 microm) is indicative of simultaneous hypercalciuria and hyperoxaluria. Calculation of the global crystal volume, especially when applied to calcium oxalates or cystine, is a clinically useful tool for the monitoring of patients suffering from primary hyperoxaluria or cystinuria. Lastly, presence of crystalluria in more than 50% of serial first voided morning urine samples is in our experience the most reliable biological marker for detecting the risk of stone recurrence in lithiasic patients. Conclusion. Crystalluria examination is an essential laboratory test for detecting and following pathological conditions, which may induce renal stone disease or alter kidney function due to urine crystals.

Role of the urinary calcium in the growth of calcium stone

We analyzed the relationship between the rate and clinical factors. The growth rate per year of the stone was measured by Nabeshima's method in 29 male patients with renal calcium stones including 7 pure calcium oxalate (CaOx) stones and 22 mixed calcium oxalate and calcium phosphate (CaOx-CaP) stones. The 24-hour urinary excretion of calcium, phosphate, uric acid and magnesium were assayed under an ambulatory free diet in 5 patients with CaOx stones and 15 with CaOx-CaP stones. The relationship between the growth rate and the urinary excretion of stone-forming parameters was examined. We found a significant positive correlation between the growth rate of calcium stones and the urinary excretion of calcium (p<0.02). In addition, the growth rate of CaOx-CaP stone was significantly higher than that of pure CaOx stone (p<0.05). In conclusion, urinary calcium is important for the growth of renal calcium stones.

Renal response to lithogenic and anti-lithogenic supplement challenges in a stone-free population group

OBJECTIVE

In South Africa, urolithiasis is extremely rare in the black population, but is common in the white population. The objective of this study was to investigate the individual effects of 5 different dietary and supplemental challenges (high dietary calcium, calcium supplement, vitamin B6 supplement, L-glutamine supplement, and L-cysteine supplement) on the urinary risk factors for calcium oxalate urolithiasis in subjects from both race groups.

DESIGN

Complete Latin Square design.

SETTING

University research laboratory.

SUBJECTS

Subjects were recruited from the student cohort of the University of Cape Town (10 male subjects from each race group). Selection criteria were no history of renal or metabolic diseases, and no chronic or acute medication. Subjects served as their own controls.

INTERVENTION

After 7 days on a self-selected standardized diet, a 24-hour baseline urine sample was collected. A second 24-hour urine sample was collected after 5 days on the prescribed dietary or supplemental challenge. These were analyzed for biochemical and physicochemical risk factors. Additionally, 24-hour dietary recall questionnaires were recorded at baseline and after the 5-day test period, and were analyzed using a food analysis program. Statistical analysis of variance was performed on all of the data.

MAIN OUTCOME MEASURES

Urine composition, relative supersaturation of urinary salts, calcium oxalate metastable limit, and Tiselius risk index.

RESULTS

None of the protocols altered any of the urinary biochemical or physicochemical risk factors in black subjects. In white subjects, the calcium diet significantly increased urinary potassium (P =.0001) and decreased the relative supersaturation of brushite (P =.035); the calcium supplement significantly decreased the Tiselius risk index (P =.014); vitamin B6 supplement significantly decreased urinary calcium (P =.016), urinary phosphate (P =.027), and the relative supersaturation of brushite (P =.004); L-glutamine supplement significantly decreased relative supersaturation of calcium oxalate (P =.01); L-cystine supplement significantly decreased urinary calcium (P =.031) and the Tiselius risk index (P =.013).

CONCLUSIONS

Because none of the challenges had an effect on the urinary risk factors in black subjects, it is speculated that a renal or gastrointestinal homeostatic adjustment occurs in this group, thereby keeping urinary concentration of substances in balance.

Is calcium oxalate nucleation in postprandial urine of males with idiopathic recurrent calcium urolithiasis related to calcium phosphate nucleation and the intensity of stone formation? Studies allowing insight into a possible role of urinary free citrate and protein

In idiopathic recurrent urolithiasis (IRCU) calcium oxalate and calcium phosphate are components of stones. It is not sufficiently known whether in urine the nucleation (liquid-solid transition) of each salt requires a different environment, if so which environment, and whether there is an impact on stone formation. Nucleation was induced by in vitro addition of oxalate or calcium to post-test meal load whole urine of male stone patients (n=48), showing normal daily and baseline fasting oxaluria. The maximally tolerated (until visible precipitates occur) concentration of oxalate (T-Ox) or calcium (T-Ca) was determined; additionally evaluated were other variables in urine, including total, complexed and free citrate (F-Cit), protein (albumin, non-albumin protein) and the clinical intensity (synonymous metabolic activity; MA) of IRCU. In the first of three trials the accumulation of substances in stone-forming urine was verified (trial-V); in the second (clinical trial 1) two strata of T-Ox (Low, High) were compared; in the third (clinical trial 2) IRCU patients (n=27) and a control group (n=13) were included to clarify whether in stone-forming urine the first crystal formed was calcium oxalate or calcium phosphate, and to identify the state of F-Cit. T-Ox was studied at the original pH (average<6.0), T-Ca at prefixed pH 6.0; the precipitates were subjected to electron microscopy and element analysis. Trial-V: Among the urinary substances accumulating at the indicated pHs were calcium, oxalate and phosphate, and the crystal-urine ratios were compatible with the nucleation of calcium oxalate, calcium-poor and calcium-rich calcium phosphate; citrate, protein and potassium also accumulated. Clinical trial 1: the two strata exhibited an inverse change of T-Ox and T-Ca, the ratio T-Ox/T-Ca and MA. The initial (before induction of Ox or Ca excess) supersaturation of calcium oxalate and brushite were unchanged, with the difference of proteinuria being borderline. Several correlations were significant (p≤0.05): urine pH with citrate and volume, protein with volume and MA, T-Ox with T-Ca and MA. Clinical trial 2: in patients with reduced urine volume and moderate urine calcium excess, the first precipitate appeared to be calcium oxalate, followed by amorphous calcium phosphate. Conversely, when the calcium excess was extreme, calcium-rich hydroxyapatite developed, followed by calcium oxalate; F-Cit, not total and complexed citrate, was decreased in IRCU vs. male controls; F-Cit rose pH-dependently, and the ratio F-Cit at original pH vs. F-Cit at pH 6.0 correlated inversely with the nucleation index T-Ox/T-Ca; MA correlated inversely with the ratio F-Cit at pH 6.0, respectively, original pH, but directly with the urinary albumin/non-albumin protein ratio. In summary 1) to study calcium oxalate and calcium phosphate nucleation in whole urine of IRCU patients is feasible; 2) at this crystallization stage the two substances, dominant in calcium stones, appear intimately linked, 3) in stone-forming urine, calcium phosphate may be ubiquitously present, likely as particles <0.22 μm; 4) together with co-precipitation of calcium oxalate and calcium phosphate, low F-Cit and alteration of proteinuria may act in concert and accelerate stones.

Synergism between the brushite and hydroxyapatite urinary crystallization inhibitors

The aim of this paper is to study possible synergic effects between crystallization-inhibitor molecules of low molecular weight on the hydroxyapatite and brushite crystal nucleation. Kinetic-turbidimetric measurements were performed to follow the nucleation process in synthetic urine at 37 degrees C. Only pyrophosphate + phytate mixture manifested synergic effects on the brushite nucleation, whereas the mixture pyrophosphate + citrate exhibited synergic effects only on the hydroxyapatite nucleation. It seems clear that synergic effects between the crystallization inhibitory capacity of some substances in urine can take place and as a consequence, the high crystallization inhibitory capacity of healthy urine could be assigned not only to the individual inhibitory capacity of each product but also to the synergic effects between different products.

Gender differences in seasonal variation of urine stone risk factors

PURPOSE

We determined whether men and women differ in urine stone risk factors during the 4 seasons of the year.

MATERIALS AND METHODS

Measurements from 28,498, 24-hour urines from stone forming patients prior to treatment were analyzed to determine whether monthly variation was significant and whether the sexes differed using ANOVA. Locations of supersaturation maxima were determined.

RESULTS

The 2 sexes showed modest sodium depletion in summer with a corresponding decrease in urine calcium but men showed a remarkable decrease in urine volume, causing high calcium oxalate supersaturation. Women had maximum calcium oxalate supersaturation in early winter because of decreasing urine volume and increasing urine calcium excretion. Urine pH was reduced in the 2 sexes during summer but the decrease was far more marked in men, who had a uric acid supersaturation spike.

PURPOSE

Overall the sexes differ markedly in the timing of stone risk. Men show a dual summer calcium oxalate and uric acid high risk, while women show a high early winter calcium oxalate high risk.

Is precipitation of calcium phosphate an important factor for the development of calcium oxalate stones in the urinary tract?

One commonly encountered problem in clinical urology is how to treat patients with calcium stone disease in a long-term perspective. At least ten per cent of the population in most parts of the world are afflicted by stone formation of which calcium stones undoubtedly dominate. The clinical problem comes from the fact that the disease is associated with a considerable recurrence rate. During a 10-year follow-up period recurrent stone formation can be expected in about half of the patients. In a Swedish epidemiological study it was shown that 30 per cent of patients who presented with their first stone had formed one or more new stones after 10 years. For those who had a history of more than one stone at the start of follow-up, the corresponding recurrence rate was 70 per cent (1). There is thus an obvious reason to provide some form of recurrence prevention at least to patients with the most severe course of the disease. Although several therapeutic alternatives today are available for such a purpose, their clinical efficacy is far from that desired. There are several explanations for our therapeutic shortcomings, but one important factor is our incomplete understanding of exactly how calcium stones form. Such knowledge is an absolute prerequisite for designing a rational effective and dynamic recurrence preventive treatment.

The diagnostic value of the phosphate levels in serum and 24-hour urine samples in patients with recurrent renal stone disease

OBJECTIVE

The aim of this study is to investigate the value of phosphate levels in serum and urine in patients with recurrent renal stone disease.

MATERIALS AND METHODS

The patients (n:60) were divided into two groups as first-time stone disease (group 1) and recurrent renal stone disease (group 2). The demographical datas and their historical information were recorded and physical examination was done. The sera and urine for 24 hr were obtained from patients to measure electrolyte levels especially phosphorus. In addition, based on presenting serum phosphate levels, patients were divided into the hypophosphatemia group, less than 2.5 mg/dl; normophosphatemia group, between 2.5-5.2 mg/dl; and hyperphosphatemia group greater than 5.2 mg/dl.

RESULTS

The mean age of study group was 45 (21-70) years. Thirty-six patients (60%) were in group 1 and 24 patients (40%) were in group 2. No statistically correlation was found between stone recurrence and phosphate levels both in serum and urine. There was only a statistical association of K levels in 24-hour urine samples between group 1 and 2.

CONCLUSION

There was no significant association between stone recurrence and initial phosphate levels in the serum or in urine. We do not propose to determine phosphate levels routinely in management of patients with stone disease.

Influence of urine pH and citrate concentration on the upper limit of metastability for calcium phosphate

PURPOSE

We determined the effects on the urine upper limit of metastability for calcium phosphate of citrate concentration and pH, and achievement of the upper limit of metastability by adding calcium or phosphate.

MATERIALS AND METHODS

The citrate concentration in aliquots of 24-hour urine samples from normal males without a history of kidney stones was increased. The upper limit of metastability was determined by the point of visible crystal formation, as confirmed by increased optical density at 620 nm. when calcium or pH was increased. In additional experiments the upper limit of metastability was determined by adding calcium or phosphate at pH 5.9 and 6.4.

RESULTS

Regardless of how the upper limit of metastability was achieved increasing the citrate concentration increased the former value by about 0.4 units per mM. citrate per l. The upper limit of metastability achieved in a given urine sample by adding phosphate or calcium did not differ. Increasing urine pH increased the upper limit of metastability.

CONCLUSIONS

Treatment with alkaline citrate salts may decrease stone formation via an increase in calcium phosphate upper limit of metastability by increasing urine citrate and by directly affecting increased pH.

Metabolic evaluation of children with urolithiasis: are adult references for supersaturation appropriate?

PURPOSE

We determined the incidence of urinary stone risk factors in pediatric patients with urolithiasis.

MATERIALS AND METHODS

Between 1998 and 2001, 71 children with urolithiasis at 2 pediatric institutions underwent metabolic evaluation. The 24-hour urine samples were analyzed outside central laboratory using adult and known pediatric references. Supersaturation and traditional metabolic parameters were determined and compared.

RESULTS

All patients had metabolic abnormalities. Calcium related abnormalities were present in 92% of children, calcium oxalate supersaturation was abnormal in 69%, calcium phosphate supersaturation was elevated in 70% and traditional calcium parameters were abnormal in 80%. While 11% of the patients had abnormal calcium phosphate or oxalate supersaturation with normal traditional calcium parameters, 10% had normal calcium oxalate or phosphate supersaturation with abnormal traditional calcium parameters. Low urinary volume was identified in 75% of the children.

CONCLUSIONS

Metabolic abnormalities are extremely common in pediatric patients with urolithiasis. Calcium related abnormalities are the most common abnormality. Urinary supersaturation values are complementary to traditional metabolic parameters and may be more sensitive predictors of recurrent stone risk. It is important to establish pediatric reference ranges to interpret these data more accurately.

Etiological role of estrogen status in renal stone formation

PURPOSE

Estrogen may protect against kidney stone formation since nephrolithiasis is more common in men than in women. Moreover, the incidence of stones rises after menopause in women. We examined the contribution of estrogen to kidney stone risk by comparing outpatient evaluations in the 2 genders, and in estrogen treated and untreated postmenopausal women.

MATERIALS AND METHODS

We reviewed the results of the initial evaluation of 1,454 adult calcium oxalate stone formers, including 1,050 men and 404 women. Of the postmenopausal women 39 and 50 were estrogen treated and untreated, respectively. Samples of urine and blood were collected 1 week after the imposition of a diet restricted moderately in sodium and calcium, and modestly in oxalate and animal protein.

RESULTS

Compared with men the daily excretion of urinary calcium, oxalate and uric acid was lower in women. Women had lower saturations of calcium oxalate and brushite as well as lower excretion of undissociated uric acid. Compared with men urinary calcium was lower in women until age 50 years, when it equaled that of men. Citrate was equal in the genders until the age 60 years, when it tended to decrease in women. Compared with nontreated postmenopausal women those treated with estrogen had lower mean 24-hour calcium plus or minus SD (155 +/- 62 versus 193 +/- 90 mg. per day, p <0.02), mean 2-hour fasting urine calcium (0.08 +/- 0.05 versus 0.12 +/- 0.09 mg./mg. creatinine, p <0.01) and mean calcium oxalate saturation (5.07 +/- 2.27 versus 6.48 +/- 3.44, p <0.05).

CONCLUSIONS

The lower risk of stone formation in women may be due to the lower urinary saturation of stone forming salts. Estrogen treatment may decrease the risk of stone recurrence in postmenopausal women by lowering urinary calcium and calcium oxalate saturation.

Influence of gender and age on calcium oxalate crystal growth inhibition by urine from relatives of stone forming patients

PURPOSE

We define the relationships between urine inhibition of calcium oxalate crystal growth and age, gender, urine chemistries and stone formation among relatives of calcium stone forming patients.

MATERIALS AND METHODS

We collected 24-hour urine samples from 366 first degree relatives of calcium stone formers. Calcium oxalate crystal growth inhibition was studied using a constant amount of dialyzed urine protein in a seeded crystallization system. Standard stone risk measurements were also performed on the urine, including supersaturation for calcium oxalate, calcium phosphate and uric acid.

RESULTS

By multivariate analysis crystal growth inhibition is strongly inversely related to the amount of protein excreted per day, and the age of the subject. When corrected for protein excretion and age, urine proteins from nonstone forming male subjects inhibited crystal growth more strongly than those from corresponding female subjects. Among stone formers the sex difference was not present.

CONCLUSIONS

Inhibition of calcium oxalate crystal growth is influenced by a complex combination of gender, age, stone formation and assay conditions. The effect of daily protein excretion is most likely a consequence of using a fixed amount of urine protein per assay. The influence of age is significant and unexplained, with the urine of young people (less than 20 years) demonstrating a vigorous ability to inhibit crystallization. In addition, the urine of nonstone forming male relatives appears to have a greater ability to inhibit crystallization than that of nonstone forming female relatives. Further use of this assay in clinical investigations must take age and gender into proper account.

Quantification of proteins extracted from calcium oxalate and calcium phosphate crystals induced in vitro in the urine of healthy controls and stone-forming patients

We have previously identified proteins extracted from calcium oxalate (CaOx) and calcium phosphate (CaP) crystals generated experimentally in vitro in whole urine of healthy controls and stone formers. No significant differences were detected between protein components in matrices of crystals obtained from both groups. The aim of the present study was to estimate the amounts of six proteins identified earlier in order to investigate the differences, if any, between healthy controls and lithiasis patients. CaOx and CaP crystals were generated in the urine samples by adding an oxalate and phosphate load, respectively. Crystals were harvested, washed, dried, and analyzed. Crystal matrix protein was extracted by demineralizing crystals with EDTA solution, analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis, and identified immunochemically using Western blot analysis. The quantity of each protein was estimated by densitometric analysis. The predominant proteins found in organic matrices of CaOx crystals induced in the urine of healthy controls were prothrombin-related proteins followed by albumin and osteopontin. In matrices of CaP crystals, the principal proteins were Tamm-Horsfall protein followed by albumin, prothrombin-related proteins and osteopontin. However, when crystals were induced in the urine of stone formers, albumin was the major component of the organic matrix of both CaOx and CaP crystals. We concluded that a subset of urinary proteins is present in crystal matrix. Among them, albumin seems to play a crucial role in kidney stone formation.

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.

The risk of renal stone formation during and after long duration space flight

BACKGROUND

The formation of a renal stone during space flight may have serious negative effects on the health of the crewmember and the success of the mission. Urinary biochemical factors and the influence of dietary factors associated with renal stone development were assessed during long duration Mir Space Station missions.

METHODS

Twenty-four-hour urine samples were collected prior to, during and following long duration space flight. The relative urinary supersaturation of calcium oxalate, calcium phosphate (brushite), sodium urate, struvite and uric acid were determined.

RESULTS

Changes in the urinary biochemistry of crewmembers during long duration spaceflight demonstrated increases in the supersaturation of the stone-forming salts. In-flight hypercalciuria was evident in a number of individual crewmembers and 24-hour dietary fluid intake and urine volume were significantly lower. During flight, there was a significant increase in brushite supersaturation.

CONCLUSIONS

These data suggest acute effects of space flight and postflight changes in the urinary biochemistry favoring increased crystallization in the urine. The effects of dietary intake, especially fluid intake, may have a significant impact on the potential for renal stone formation. Efforts are now underway to assess the efficacy of a countermeasure to mitigate the increased risk.

Proportional reduction of urine supersaturation during nephrolithiasis treatment

PURPOSE

During metabolic stone therapy, urine supersaturation decreases in proportion to pretreatment levels. We gauge the quantitative contribution of regression to the mean for reducing urine supersaturation from high pretreatment to lower values during therapy.

MATERIALS AND METHODS

The 24-hour urine supersaturations for calcium oxalate, calcium phosphate and uric acid were measured on 2 pretreatment and at least 1 treatment 24-hour collection for each of the 2,667 patients in 2 networks and at a university based specialty clinic. Changes in supersaturation between the first and second pretreatment collections were an estimate of random change and compared to therapeutic changes.

RESULTS

Supersaturations decreased between the first and second pretreatment collections, proportional to the supersaturation in the first collection. However, the magnitude of this effect was minor compared to therapeutic changes. Also, mean change between pretreatment collections was 0, whereas mean change with therapy was greater than 0 for all 3 supersaturations.

CONCLUSIONS

Although regression to the mean can be detected, it cannot be responsible for the decrease in urine supersaturation with therapy or the fact that the decrease is proportional to pretreatment mean supersaturation. The mechanisms responsible for proportional reduction remain to be clarified.