A urinary calcium-citrate index for the evaluation of nephrolithiasis

Pharmacologic treatment of kidney stones: Current medication and pH monitoring

Nephrolithiasis is a globally prevalent urologic condition associated with significant morbidity and patient discomfort. Current management of kidney stones includes both surgical and pharmacologic interventions. Though surgery may be necessary under certain circumstances, pharmacologic treatment is a more affordable, readily available, and a less invasive option for patients. A comprehensive scoping review was conducted to summarize the available literature on the pharmacologic strategies for managing the predominant stone types including calcium oxalate, calcium phosphate, uric acid, struvite, and cystine stones. Central to these therapeutic approaches is the regulation of factors such as urine pH, stone crystallization, and patient metabolics that precipitate stone development and growth. This review highlights the pharmacological options available for treating each kidney stone type, emphasizing the importance of patient tailored medical management that should be considered by every physician.

Urolithiasis Problems in Finishing Pigs

This paper describes cases of urolithiasis in fattening pigs on two farms (A and B). Bladder rupture due to urethral obstruction with calculi was the principal finding during the necropsy of the pigs. An in-depth diagnostic examination was performed to elucidate possible pathophysiological mechanisms, namely Fourier-transform infrared spectrophotometry (FT-IR) analysis of the uroliths, blood analysis (farm A: 5 samples, farm B: 10 samples) for assessing concentrations of minerals, the bone resorption marker cross-linked C-telopeptide of type 1 collagen (CTX), parathyroid hormone (PTH), and vitamin D components, biochemical urinalysis (farm A: 5 samples, farm B: 7 samples), microscopic examination of urinary sediment (Farms A and B: 7 samples each), mineral composition of the feed, and analysis of the drinking water. Calcium carbonate was the main component found in stones from both farms, and calcium carbonate and struvite were the main components found in crystals from farms A and B, respectively. On farm A, urinary calcium excretion and urinary pH were high; on farm B, urinary phosphorus was high and urinary calcium was low with a normal urinary pH. The mineral compositions of the feed and drinking water were similar on both farms and could therefore not explain the difference between the two farms. Disturbances in calcium and phosphorus absorption and homeostasis might have been involved in these problems. Further research should focus on the calcium, phosphorus, and vitamin D levels in the feed and take into account other factors, such as the absorption and excretion of minerals due to gut and urinary microbiota.

Numerical characterization of astronaut CaOx renal stone incidence rates to quantify in-flight and post-flight relative risk

Changes in urine chemistry potentially alter the risk of renal stone formation in astronauts. Quantifying spaceflight renal stone incidence risk compared to pre-flight levels remains a significant challenge for assessing the appropriate vehicle, mission, and countermeasure design. A computational biochemistry model representing CaOx crystal precipitation, growth, and agglomeration is combined with a probabilistic analysis to predict the in- and post-flight CaOx renal stone incidence risk ratio (IRR) relative to pre-flight values using 1517 astronaut 24-h urine chemistries. Our simulations predict that in-flight fluid intake alone would need to increase from current prescriptions of 2.0–2.5 L/day to ~3.2 L/day to approach the CaOx IRR of the pre-flight population. Bone protective interventions would reduce CaOx risk to pre-flight levels if Ca excretion alone is reduced to <150 mg/day or if current levels are diminished to 190 mg/day in combination with increasing fluid intake to 2.5–2.7 L/day. This analysis provides a quantitative risk assessment that can influence the critical balance between engineering and astronaut health requirements.

Do Infection-Associated Stone Subtypes Behave the Same Clinically? A Retrospective Bi-center Study

Introduction and Objectives Infection associated renal stones are commonly composed of magnesium-ammonium-phosphate (MAP) and carbonate apatite (CA). The clinical implications of these two different, but closely related stone types, are unknown. We sought to compare the clinical, microbiologic, and metabolic characteristics of patients with MAP and CA stone types. Methods We retrospectively reviewed the medical records of patients from two centers (one in the USA and one in Israel) who underwent ureteroscopy or percutaneous nephrolithotomy between 2012 and 2020 and identified patients with a predominant stone analysis component of CA or MAP and clinical data supporting an infection stone. We analyzed and compared demographic data, medical history, post-operative fever, stone and urinary microbiology, and 24-hour urine studies. Results A total of 79 and 75 patients met the inclusion criteria for the MAP and CA cohorts, respectively. No significant difference was found in patient demographics or comorbidities between the MAP and CA cohort. Female predominance was noted in both. Though there were no significant differences in 24-hour urine parameters between the cohorts, hypercalciuria was common in both cohorts (38% and 32% of patients in the MAP and CA cohorts, respectively). Gram negative bacteria were more common in the MAP stone cultures. Post-operative fever was significantly more common in the MAP cohort (14.7% vs 3.8%, p<0.016). Conclusions: MAP and CA stone formers share similar demographic characteristics with a clear female predominance. MAP stones patients appear more likely to develop postoperative fever, possibly related to a higher occurrence of gram-negative bacteria in the stone cultures of the MAP cohort. Although there were no significant differences amongst metabolic parameters, hypercalciuria was noted in approximately a third of the cohort. The clinical significance of this finding is yet to be determined.

Urine osmolality predicts calcium-oxalate crystallization risk in patients with recurrent urolithiasis

Our aim was to investigate the validity of osmolality from 24-h urine collection in examining the risk for calcium-oxalate (CaOx) kidney stone formation in patients with recurrent urolithiasis. Three hundred and twelve subjects (males/females: 184/128) from France with a history of recurrent kidney stones from confirmed or putative CaOx origin were retrospectively included in the study (46 ± 14 years, BMI: 25.3 ± 5.0 kg·m^-2). Tiselius' crystallization risk index (CRI) was calculated based on urinary calcium, oxalate, citrate, magnesium, and volume from 24-h samples. The diagnostic ability of 24-h urine osmolality to classify patients as high risk for kidney stone crystallization was examined through the receivers operating characteristics analysis. High risk for CaOx crystallization was defined as CRI > 1.61 and > 1.18, for males and females, respectively. The accuracy of urine osmolality to diagnose risk of CaOx stone formation (AUC, area under the curve) for females was 84.6%, with cut-off point of 501 mmol·kg^-1 (sensitivity: 83.3%, specificity: 76.0%). Males had AUC of 85.8% with threshold of 577 mmo·kg^-1 (sensitivity: 85.5%, specificity: 77.6%). A negative association was found between 24-h urine volume and osmolality (r = - 0.63, P < 0.001). Also, a positive association was found between 24-h urine osmolality and CRI (r = 0.65, P < 0.001), as well as urea excretion with CRI (r = 0.37, P < 0.001). In conclusion, urine osmolality > 501 and > 577 mmol·kg^-1, in female and in male, respectively, was associated with a risk for CaOx kidney stone formation in patients with a history of recurrent urolithiasis. Thus, when CaOx origin is confirmed or suspected, 24-h urine osmolality provides a simple way to define individualized target of urine dilution to prevent urine crystallization and stone formation.

Effect of parathyroidectomy on renal stone recurrence

Parathyroidectomy (PTX) is routinely performed in hypercalciuric renal stone patients with primary hyperparathyroidism (PHPT). However, some data indicate a persistent stone activity following PTX, raising the issue of the link between PHPT and stone disease. We performed an observational study on 30 renal stone patients diagnosed with PHPT. Patients were selected among 1448 hypercalciuric patients referred in our department for a diagnostic evaluation. Patients with no parathyroid surgery or any biological follow-up were excluded. Clinical and biological data (including 24-h urine collection and a calcium load test) were collected before and within 12 months following surgery. Stone recurrence was evaluated by direct phone contact (median 43 months). Comparison of biological data before and after surgery showed a significant decrease of ionized calcium and serum parathyroid hormone after PTX. All stones contained calcium-dependent species such as carbapatite, brushite or dihydrate calcium oxalate. Urine saturation indexes and calciuria significantly decreased after surgery (from 9.9 to 5.9 mmol/d, p < 0.0001), but a persistent hypercalciuria was detected in 47% of patients. The other stone risk factors including diuresis stayed similar. Stone activity that was increasing (from 0.20-0.30 to 0.50-0.75/year) the 2 years before PTX, significantly decreased after surgery [0.05-0.15/year (p < 0.001)]. PTX in calcium-dependent renal stone formers with PHPT significantly decreases both stone recurrence and urine saturation indexes. However, PTX unmasked an underlying renal stone disease related to idiopathic hypercalciuria in half of patients with a remaining stone activity, testifying the need for patient's follow-up to prevent stone recurrence.

Association of urinary sex steroid hormones with urinary calcium, oxalate and citrate excretion in kidney stone formers

BACKGROUND

Sex-specific differences in nephrolithiasis with respect to both distribution of prevalence and stone composition are widely described and may be influenced by sex hormones.

METHODS

We conducted a cross-sectional analysis of the relationship between 24-hour urinary sex hormone metabolites measured by gas chromatography-mass spectrometry with urinary calcium, oxalate and citrate excretion in a cohort of 628 kidney stone formers from a tertiary care hospital in Switzerland, taking demographic characteristics, kidney function and dietary factors into account.

RESULTS

We observed a positive association of urinary calcium with urinary testosterone and 17β-estradiol. Positive associations of urinary calcium with dehydroepiandrosterone, 5α-DH-testosterone, etiocholanolone, androsterone, and estriol were modified by net gastrointestinal alkali absorption or urinary sulfate excretion. As the only sex hormone, dehydroepiandrosterone was inversely associated with urinary oxalate excretion in adjusted analyses. Urinary citrate correlated positively with urinary testosterone. Associations of urinary citrate with urinary androsterone, 17β-estradiol and estriol were modified by urinary sulfate or sodium, or by sex.

CONCLUSIONS

Urinary androgens and estrogens are significantly associated with urinary calcium and citrate excretion, and associations are in part modified by diet. Our data furthermore reveal dehydroepiandrosterone as a novel factor associated with urinary oxalate excretion in humans.

Mechanisms for falling urine pH with age in stone formers

One of the main functions of the kidney is to excrete an acid load derived from both dietary and endogenous sources, thus maintaining the pH of other fluids in the body. Urine pH is also of particular interest in stone formers, since it determines the presence of either calcium phosphate or uric acid content in stones. Others have noted in epidemiological studies a rise in incidence of low pH-dependent uric acid stones with age, coinciding with a decrease in the incidence of high pH-dependent phosphate stones. Taken together, these trends are suggestive of a longitudinal decline in urine pH in stone-forming patients, and, if true, this could explain the observed trends in stone incidence. We studied 7,891 stone formers, all of whom collected a 24-h urine sample and matching serum. Multivariate modeling revealed that urine pH did indeed fall with age and particularly between the ages of 20 and 50 yr old in both men and women. We sought to explain this trend through the inclusion of traditionally understood determinants of urine pH such as urinary buffers, estimates of glomerular filtration, and dietary acid load, but these, taken together, accounted for but a small fraction of the pH fall. Gastrointestinal anion absorption was the strongest predictor of urine pH in all age groups, as we have previously reported in middle-aged normal men and women. However, we found that, despite a decreasing urine pH, gastrointestinal anion absorption increased monotonically with age. In fact, after adjustment for gastrointestinal anion absorption, urine pH declined more markedly, suggesting that bicarbonate-producing anion absorption is regulated in a manner that offsets the decline of urine pH.

Insights about urinary hippuric and citric acid as biomarkers of fruit and vegetable intake in patients with kidney stones: The role of age and sex

OBJECTIVES

Urinary hippuric acid (HA) and citrate can represent useful biomarkers of fruit and vegetable (FAV) intake in nephrolithiasis. However, their clinical significance across the life span has been poorly investigated. The aim of this study was to investigate the association between the two biomarkers with FAV intake across different age groups and sexes in a large group of stone formers (SFs).

METHODS

SFs undergoing baseline 24-h urinary collection for metabolic profile of lithogenic risk at our institution were consecutively enrolled for a 6-y time span (N = 1185; 625 men). HA and citrate excretions were determined by ion chromatography and ultraviolet method, respectively. SFs completed a food frequency questionnaire on the intake of FAV. Stepwise logistic regression was applied to investigate factors associated with very low FAV (≤1 servings/d) and analysis of covariance to compare citrate and HA excretion across age groups and sexes.

RESULTS

Very low FAV intake prevalence declined with age (P_trend < 0.001), and was inversely associated with HA and citrate excretion (P < 0.001) in a stepwise logistic regression model. A significant increasing trend was verified for both biomarkers across age groups until the age of 65 for HA (P < 0.001) and 55 for citrate (P < 0.001). Citrate excretion significantly declined after the age of 65, and was higher in women than men in adult age groups, regardless of FAV intake.

CONCLUSIONS

Both urinary citrate and HA were positively associated with FAV intake in SFs. However, unlike HA, citrate excretion was significantly influenced by the female sex and by older age.

Mechanism for higher urine pH in normal women compared with men

Regulation of acid-base metabolism maintains the pH of body fluids within a tight range. Urine pH (UpH) is also regulated under normal conditions. Median pH of 24-h urines is ~6, but others have noted that UpH in women is higher than men, which has been attributed to differences in diet. If true, it would help to explain the fact that calcium phosphate stones, which form at higher urine pH, are much more common in women than in men. We studied 14 normal subjects (7 men and 7 women) fed identical meals in a Clinical Research Center. Urine and blood samples were collected during fasting and after meals. UpH of women (6.74 ± 0.11) exceeded that of men (6.07 ± 0.17) fed, but not fasting, and UpH rose significantly with meals in women but not men. Serum and urine total CO₂ rose with meals in women but not men, and in women net acid excretion fell to zero during the fed period. In a general linear model adjusted for age, sex, and weight, net gastrointestinal anion uptake was the main predictor of UpH and was significantly higher in women (3.9 ± 0.6) than men (1.8 ± 0.7) in the fed period. Urine citrate, an anion absorbed by the gastrointestinal tract, was higher in women than men in the fed state, and fractional excretion of citrate was higher in women than men. The higher fed UpH in women is related to a greater absorption of food anions and raises 24-h UpH.

Possible role of elevated serum testosterone in pathogenesis of renal stone formation

Background:

Urolithiasis or renal stone formation occurs with three times higher frequency in males and decreases with age in parallel with the serum testosterone levels, suggesting a role played by male sex hormones. Androgens appear a promotion action and estrogens an inhibitory action on kidney stone formation in several animal models suggesting a study to be carried out to deduce the role played by serum testosterone in the formation of renal stones.

Aim:

The aim of this study is to define the involvement of serum total testosterone, free testosterone, and dihydrotestosterone in the pathogenesis of urolithiasis in males by comparing the results with healthy males with no present or past history of urolithiasis as controls.

Materials and Methods:

A case–control study was undertaken with 108 participants: 78 males diagnosed with urolithiasis and 30 age-matched healthy males.

Results:

The difference between mean age and body mass index of patients and controls were found to be nonsignificant. The total serum testosterone levels, serum dihydrotestosterone levels, were found to be higher in patients when compared to controls, and the difference was found to be significant. The levels of free testosterone and serum estradiol were also found to be higher in urolithiatic patients.

Conclusion:

The study demonstrates that elevated levels of serum testosterone and serum dihydrotestosterone might be involved in increased incidences of stone formation. The higher levels of estradiol do not seem to be a protective factor in males with urolithiasis with higher serum testosterone levels.

Induced urinary crystal formation as an analytical strategy for the prediction and monitoring of urolithiasis and other metabolism-related disorders

Crystal formation reflects the entire composition of the surrounding solution. In case of urolithiasis, induced crystal formation in native urine has led to the development of the Bonn-Risk-Index (BRI), a valuable tool to quantify an individual's risk of calcium oxalate urolithiasis. If the progression of a disease is associated with characteristic changes in the activities of urinary components, this leads to an altered urinary crystallisation capacity. Therefore, the results of induced urinary crystal formation can be used to detect and monitor any disease linked to the altered urinary composition. Since crystal formation inherently takes into account the entire urinary composition, the influence of the disease on individual urinary parameters does not have to be known in order to monitor the consequent pathologic alterations. In this paper, we review the background of urinary crystal formation analysis and describe its established application in urolithiasis monitoring as well as potential further fields of clinical application.

Clinical and metabolic evaluation of patients with history of renal calculi in Qazvin, Iran

BACKGROUND

Nephrolithiasis is a common clinical disorder with significant health and economic burden. We conducted this study to evaluate clinical and metabolic parameters in adult patients with history of renal calculi.

MATERIALS AND METHODS

A total of 213 patients with history of nephrolithiasis participated in this study. Evaluation included the measurement of serum calcium, uric acid, parathormone, renal function tests, urinalysis, and urinary tests for cystinuria. Also, parameters such as volume, creatinine, calcium, uric acid, citrate, and oxalate levels were measured on 24-h urine. All patients underwent urinary tract system sonography.

RESULTS

Of total patients, 52% were males and 48% females. The mean age was 45.16 ± 13.16 years. Also, 51.2% of subjects had positive family history of nephrolithiasis. The mean body mass index was (26.8 ± 4.2) kg/m(2). The mean 24-h urine biochemical profiles were volume (1,748 ± 860 ml), Ca (183 ± 115), uric acid (544 ± 220), citrate (490 ± 351), and oxalate (17.1 ± 15.3) mg/day; urine calcium to creatinine ratio (0.15 ± 0.10) mg/mg, and urine calcium to weight ratio (2.4 ± 1.7) mg/kg. While there were weak positive correlations between the body mass index and urinary calcium (r = 0.101, P < 0.001) and uric acid (r = 0.200, P < 0.001), a weak negative correlation with urine pH (r = -0.104, P < 0.001) was found.

CONCLUSIONS

Urine calcium, uric acid, and oxalate excretion were low in our patients while urine citrate was relatively high. Higher BMI maybe a risk factor for nephrolithiasis.

Serum estradiol and testosterone levels in kidney stones disease with and without calcium oxalate components in naturally postmenopausal women

Objective

Epidemiological data reveal that the overall risk for kidney stones disease is lower for women compared to age-matched men. However, the beneficial effect for the female sex is lost upon menopause, a time corresponding to the onset of fall in estrogen levels. The aim of this study was to describe the serum estradiol (E2) and testosterone (T) characteristics of naturally postmenopausal women with kidney stones.

Methods

113 naturally postmenopausal women with newly diagnosed kidney stones (aged 57.4±4.98 years) and 84 age frequency matched stone-free controls (56.9±4.56 years) were validly recruited in the case-control study. The odds ratios (ORs) for the associations between sex hormones and kidney stones were estimated with logistic regression models, adjusting for demographic data and medical history. Patients were also stratified analyzed according to stone components (calcium oxalate stones [COS]; non-calcium oxalate stones [NCOS]).

Results

Serum E2 (21.1 vs. 31.1 pg/ml) was significantly lower in kidney stones patients compared to controls. Post-hoc analysis demonstrated that this effect was driven by COS patients (p<0.001). According to tertiles of the E2 levels, a significant higher frequency of COS was seen in the lowest E2 group (p <0.001). Multiple logistic regression analysis identified E2 level as a strong factor that was independently associated with the risk for COS (per 1 SD increase, OR=0.951, 95% confidence interval [CI] = 0.919-0.985; highest: lowest tertile, OR=0.214, 95%CI = 0.069-0.665). However, serum T levels did not significantly differ among the groups.

Conclusions

Naturally postmenopausal women with higher remaining estradiol levels appear less likely to suffer from kidney calcium oxalate stones. However, no correlation was found between serum T level and kidney stones. These findings support the hypothesis that higher postmenopausal endogenous estrogens may protect against kidney stones with ageing.

Effects of Sex on Intra-Individual Variance in Urinary Solutes in Stone-Formers Collected from a Single Clinical Laboratory

Background/Aims

Our work in a rodent model of urinary calcium suggests genetic and gender effects on increased residual variability in urine chemistries. Based on these findings, we hypothesized that sex would similarly be associated with residual variation in human urine solutes. Sex-related effects on residuals might affect the establishment of physiological baselines and error in medical assays.

Methods

We tested the effects of sex on residual variation in urine chemistry by estimating coefficients of variation (CV) for urinary solutes in paired sequential 24-h urines (≤72 hour interval) in 6,758 females and 9,024 males aged 16–80 submitted to a clinical laboratory.

Results

Females had higher CVs than males for urinary phosphorus overall at the False Discovery Rate (P<0.01). There was no effect of sex on CV for calcium (P>0.3). Males had higher CVs for citrate (P<0.01) from ages 16–45 and females higher CVs for citrate (P<0.01) from ages 56–80, suggesting effects of an extant oestral cycle on residual variance.

Conclusions

Our findings indicate the effects of sex on residual variance of the excretion of urinary solutes including phosphorus and citrate; differences in CV by sex might reflect dietary lability, differences in the fidelity of reporting or genetic differentiation in renal solute consistency. Such an effect could complicate medical analysis by the addition of random error to phenotypic assays. Renal analysis might require explicit incorporation of heterogeneity among factorial effects, and for sex in particular.

Renal function and kidney length in preterm infants with nephrocalcinosis: a longitudinal study

Renal injury in early life may lead to hypertension and renal disease in adulthood. In this prospective study, we estimated renal glomerular and tubular function and kidney length (KL) during the first 2 years of life of preterm infants with nephrocalcinosis (NC) associated with prematurity. The study cohort comprised 107 preterm children, 63 with NC and 44 control subjects without NC who were matched for gender, gestational age and birth weight. Kidney function was estimated based on measurements of serum creatinine (Scr), estimated glomerular filtration rate (eGFR), fractional excretion (FE) of sodium (Na), potassium (K), phosphate (P), magnesium (Mg) and uric acid (UA) and on the ratios of urinary Ca, oxalate (UOx) and citrate (UCit) to urinary creatinine (UCa/Ucr, UOx/Ucr and UCit/Ucr, respectively) calculated from morning urine collections. KL was measured by ultrasonography. Measurements were made at 40 weeks postmenstrual age and at 3, 6, 12 and 24 months of age. At 3 and 6 months, the NC group had higher UCa/Ucr, FEK and FEUA than the control group; at 12 months, only the UCa/Ucr and FEUA was still higher. The UCa/UCit ratio was higher in the NC group. Scr and eGFR did not differ between the groups at any time point. The NC group had a shorter KL up to 12 months of life (left kidney) or 24 months (right kidney). Based on these results, we conclude that NC in the preterm infants enrolled in our study was associated with impaired renal tubular function and a shorter KL in the first year of life.

Localization, etiology and impact of calcium phosphate deposits in renal allografts

Hypercalcemia, hypophosphatemia and renal phosphate wasting are common after kidney transplantation. Animal data suggest that these alterations in mineral metabolism may contribute to calcium phosphate (CaPhos) deposition in the kidney and renal dysfunction. We tested the hypothesis that CaPhos deposition is highly prevalent in the early posttransplant period and is related to a disturbed mineral metabolism. For this purpose, biomarkers of mineral metabolism and renal calcium and phosphorus handling were prospectively assessed in 201 renal transplant recipients. CaPhos deposits were observed in 4.6, 30.4 and 24.7% of protocol biopsies obtained at the time of engraftment, and 3 and 12 months thereafter, respectively. In multivariate logistic regression analysis, high calcium and low serum phosphorus levels were independently associated with renal CaPhos deposition at month 3. The extent of CaPhos deposition correlated significantly with the severity of mineral metabolism disturbances. Renal function after a mean follow-up of 33 months was similar in patients with and without CaPhos deposition at month 3. In conclusion, our data demonstrate that CaPhos deposition is highly prevalent in the early posttransplant period and suggest that a disordered mineral metabolism is implicated in its pathogenesis. The clinical relevance of CaPhos deposition remains to be established.

Assessment of crystallization risk formulas in pediatric calcium stone-formers

The pathogenesis of calcium urolithiasis involves complex interactions of urinary promoters and inhibitors of crystallization. A variety of risk formulas have been established to approximate these interactions for clinical evaluation, and the aim of our study was to determine their usefulness as predictors of stone formation. The study cohort comprised 126 patients (63 boys and 63 girls) aged 6.7-18 years (mean age 14.1 +/- 2.9 years) with calcium urolithiasis (61 with chemically confirmed calcium oxalate stones and 65 children with a strong clinical suspicion of this type of urolithiasis). Of these, 36 children were classified as recurrent stone-formers, whereas the remaining 90 had experienced only one stone episode. The values obtained were compared to those of a control group of 60 age- and gender- matched healthy children. A number of crystallization risk indices were calculated from analytes obtained in 24-h urine: calcium/magnesium ratio (Ca/Mg), calcium/citrate ratio (Ca/Cit), (calcium x oxalate)/(magnesium x citrate) ratio (CaOx/MgCit), relative urinary CaOx supersaturation (RS(CaOx)), CaOx activity product index (AP(CaOx)), and standardized CaOx activity product index (AP(CaOx stand)). All indices, except for the AP(CaOx) index, were significantly higher in stone-formers than in the controls. The Ca/Mg, Ca/Cit, CaOx/MgCit, AP(CaOx), and AP(CaOx stand) indices were significantly higher in recurrent stone-formers than in first-episode ones. However, the determination of precise cutoffs between pathological and non-pathological values was problematic due to a considerable overlap of individual values. Based on our results, we conclude that calculation of the majority of risk indices may play a rather supplementary role in the evaluation of children with calcium urolithiasis.

Urine calcium/citrate ratio in children with hypercalciuric stones

Hypercalciuria is a common cause for stone formation in children. The aim was to delineate the role of urinary citrate in hypercalciuric children for protection against calcium stone formation. We evaluated random urine calcium, citrate, and creatinine in 149 controls, 78 hypercalciuric nonstone formers, and 34 hypercalciuric children with stone. Urine citrate/creatinine was highest in hypercalciuric nonstone formers 899 +/- 351 compared with controls 711 +/- 328 and stone formers 595 +/- 289 (p < 0.01 vs. both). Calcium/creatinine ratio was similar in hypercalciuric stone and nonstone formers, but significantly higher than controls. Consequently, urine calcium/citrate ratio (mg/mg) increased from control 0.17 +/- 0.17 to 0.41 +/- 0.23 (p < 0.001) in hypercalciuric nonstone formers, and to 0.65 +/- 0.46 in stone formers (p < 0.001 compared with other groups). Area under receiver operating characteristic curve combined with multilevel risk analyses found calcium/citrate ratio of 0.326 to provide good discrimination between control and stone formers. We found 5th percentile for random urine citrate/creatinine ratio in school-aged children to be 176 mg/g, elevated urinary citrate excretion in hypercalciuric children to be protective against stone formation, and urine calcium/citrate ratio to be a good indicator for risk of stone formation. Whether intervention in hypercalciuric children to lower urine calcium/citrate <0.326 will provide protection against stone formation needs to be studied.

Urine protein markers distinguish stone-forming from non-stone-forming relatives of calcium stone formers

We have investigated urine protein inhibitors of calcium oxalate crystallization to determine whether variations in these proteins are associated with kidney stone disease and whether protein measurements improve the identification of stone formers compared with conventional risk factors (RF). Using Western blotting, we studied variations in the electrophoretic mobility patterns and relative abundances of crystallization-inhibitory proteins in urine from 50 stone-forming (SF) and 50 non-stone-forming (NS) first-degree relatives of calcium SF patients, matched by gender and age. Standard urine chemistry stone risk measurements were also made. Multivariate discriminant analysis was used to test the association of these proteins with nephrolithiasis. Differences in form and abundance of several urine proteins including inter-alpha-trypsin inhibitor (ITI), prothrombin fragment 1 (PF1), CD59, and calgranulin B (calB) were found to be associated with stone formation. By multivariate discriminant analysis, measurements of forms of PF1, ITI, and calB in men and ITI and CD59 in women, classified 84% of men and 76% of women correctly by stone status. In contrast, standard urine chemistry RF identified only 70% of men correctly and failed to distinguish female SF from NS. Thus a small subset of protein measurements distinguished SF from NS far better than conventional RF in a population of relatives of calcium SF, illustrating the significant association of these proteins with stone disease. Variations in these proteins may serve as markers of stone disease activity or vulnerability to recurrence and may provide new insights into mechanisms of stone formation.

Are changes in urinary parameters during pregnancy clinically significant?

We aimed to objectively determine changes in the various urinary parameters along with CaOx saturation level during pregnancy. The study included 15 pregnant women who had no known diseases and were taking no medication except prenatal supplements. Mean age of the patients was 26 years (range 20-30). In all of them, this study was carried out in each trimester and 3 months post partum. All participants were followed up, and blood and urine samples were obtained during the pregnancy and during 3 months post partum. All subjects collected 24-h urine samples. The pregnant women had hypercalciuria in all three trimesters. Except for the first trimester, urine calcium levels in all trimesters were significantly higher when compared with the post-partum period (P<0.01 for second trimester, P<0.05 for third trimester). Urine oxalate level in post-partum period was significantly higher than urine oxalate levels in each trimester (P<0.05). The urine citrate levels were similarly higher than normal levels in three trimesters. Urine citrate level of the post-partum period was in normal reference ranges. This difference was not statistically significant (P>0.05). We believe that hypercalciuria encountered at pregnancy is a reversible physiologic condition. Also, citrate and magnesium as urinary inhibitors increased in urine during gestation preventing stone formation. We think that long time periods are needed for hypercalciuria to be able to lead to the formation of urinary calculi in pregnant women (except women having a positive family history). Therefore, we think that the pregnancy alone does not predispose to a suitable condition for calculi.

Effect of potential renal acid load of foods on urinary citrate excretion in calcium renal stone formers

The aim of this study was to investigate the influence of the potential renal acid load (PRAL) of the diet on the urinary risk factors for renal stone formation. The present series comprises 187 consecutive renal calcium stone patients (114 males, 73 females) who were studied in our stone clinic. Each patient was subjected to an investigation including a 24-h dietary record and 24-h urine sample taken over the same period. Nutrients and calories were calculated by means of food composition tables using a computerized procedure. Daily PRAL was calculated considering the mineral and protein composition of foods, the mean intestinal absorption rate for each nutrient and the metabolism of sulfur-containing amino acids. Sodium, potassium, calcium, magnesium, phosphate, oxalate, urate, citrate, and creatinine levels were measured in the urine. The mean daily PRAL was higher in male than in female patients (24.1+/-24.0 vs 16.1+/-20.1 mEq/day, P=0.000). A significantly (P=0.01) negative correlation (R=-0.18) was found between daily PRAL and daily urinary citrate, but no correlation between PRAL and urinary calcium, oxalate, and urate was shown. Daily urinary calcium (R=0.186, P=0.011) and uric acid (R=0.157, P=0.033) were significantly related to the dietary intake of protein. Daily urinary citrate was significantly related to the intakes of copper (R=0.178, P=0.015), riboflavin (R=0.20, P=0.006), piridoxine (R=0.169, P=0.021) and biotin (R=0.196, P=0.007). The regression analysis by stepwise selection confirmed the significant negative correlation between PRAL and urinary citrate (P=0.002) and the significant positive correlation between riboflavin and urinary citrate (P=0.000). Urinary citrate excretion of renal stone formers (RSFs) is highly dependent from dietary acid load. The computation of the renal acid load is advisable to investigate the role of diet in the pathogenesis of calcium stone disease and it is also a useful tool to evaluate the lithogenic potential of the diet of the individual patient.

The use of risk indices: do they predict recurrence? Yes, they (at least some) do

A suitable and advisedly used risk index is an effective tool for improving prevention, therapy monitoring and classification of almost unmanageable amounts of analysis data and diagnoses. In contrast to statistically founded indices, causality-based risk indices can provide a fundamental insight into the mechanisms of the underlying pathology. However, understanding of stone formation as the result of many linked and often non-linear individual processes must be further improved. Only in this way can risk indices be optimized or better ones be developed. We are confident that, with consistent research efforts, science will be able to predict recurrence of stone formation more accurately within the next couple of years.

The use of risk indices: do they predict recurrence?

A risk index which would reliably predict the likelihood of stone recurrence in the patient with renal calculi would help the clinician to select appropriate preventative therapy. However, none of the indices developed to date combines easy applicability in usual clinical settings with sufficient predictive power to be useful to the clinician in making treatment decisions.

Artificial neural networks for assessing the risk of urinary calcium stone among men

The pathophysiology of idiopathic calcium oxalate nephrolithiasis involves metabolic abnormalities. Previous studies gave conflicting results about the metabolic factors in stone formers. Artificial neural networks (ANN) are new methods based on computer programming that have outperformed conventional methods in prediction of outcomes in different medical applications. The aim of our study was to compare with ANN the clinical and biochemical parameters implicated in urinary calcium stone between stone formers (SF) and controls (C). We compared 11 clinical and biochemical variables among 119 male idiopathic calcium oxalate SF and 96 C by univariate and multivariate statistical analyses. Univariate analyses included discriminant analysis, logistic regression analysis, and ANN. For multivariate analyses, stepwise discriminant analysis and ANN were performed. Variables included age, body mass index (BMI), family history of nephrolithiasis, supersaturation with respect to calcium oxalate, calcemia, and 24-h urinary calcium, oxalate, uric acid, urea, sodium, and citrate. With univariate and multivariate analyses, ANN were as efficient as classical statistical analyses in discriminating the different parameters. The sensitivity, the specificity, and the percentage of correctly classified patients were similar in all analyses. With ANN, supersaturation (receiver operating characteristic, ROC curves index 0.73) and urea (ROC 0.72) were the most discriminant followed by family history and urinary calcium (ROC 0.67). ROC index was 0.63 for citrate, 0.61 for oxalate and urate, 0.60 for sodium and calcemia, 0.58 for age, and 0.56 for BMI, but these parameters were not statistically different between SF and C. ANN gave additional information since they made it possible to determine the cut-off values of the parameters and their predictive power. Cut-off values for being a stone former were 8.9 for supersaturation and 363 mmol/day for urinary urea with a predictive power of 0.69 and 0.70, respectively. Univariate and multivariate analysis evidenced supersaturation and 24-h urinary urea excretion as the most discriminant parameters between the two populations. In addition to high supersaturation, the negative impact of protein intake was confirmed.

Kidney stone disease

About 5% of American women and 12% of men will develop a kidney stone at some time in their life, and prevalence has been rising in both sexes. Approximately 80% of stones are composed of calcium oxalate (CaOx) and calcium phosphate (CaP); 10% of struvite (magnesium ammonium phosphate produced during infection with bacteria that possess the enzyme urease), 9% of uric acid (UA); and the remaining 1% are composed of cystine or ammonium acid urate or are diagnosed as drug-related stones. Stones ultimately arise because of an unwanted phase change of these substances from liquid to solid state. Here we focus on the mechanisms of pathogenesis involved in CaOx, CaP, UA, and cystine stone formation, including recent developments in our understanding of related changes in human kidney tissue and of underlying genetic causes, in addition to current therapeutics.

Influence of estrus status on urinary chemical parameters related to urolithiasis

The present study examines the urinary chemical parameters related to urolithiasis in healthy female volunteers during premenopause and menopause, and discusses the role of menopause in stone formation. We investigated 24-h urine parameters associated with urinary stones and focused upon estrus status. Participants comprised 30 healthy women, 15 childless, premenopausal women and 15 menopausal women without a history of urolithiasis. Our results showed that menopausal women have lower citrate and higher calcium excretion, which might enhance calcium stone crystallization. We propose that the estrus status of female patients should be considered when evaluating metabolic abnormalities.

Oral L-arginine supplementation ameliorates urinary risk factors and kinetic modulation of Tamm-Horsfall glycoprotein in experimental hyperoxaluric rats

BACKGROUND

Oral supplementation of l-arginine (l-arg) is found to be beneficial in many kidney disorders. We determined whether l-arg supplementation safeguards the renal epithelial cell damage induced by hyperoxaluria with excretion of urinary marker enzymes and lithogenic salts with special reference to Tamm-Horsfall glycoprotein (THP).

METHODS

Hyperoxaluria was induced by 0.75% ethylene glycol (EG) in drinking water. l-Arg was co-supplemented at the dose of 1.25 g/kg b.w. orally for 28 days. At the end of experimental period, 24-h urine samples were collected in all the experimental groups. Isolation and purification of THP was carried in rat urine and were subjected to spectrophotometric crystallization assay and calcium-(14)C-oxalate binding studies. Determination of the lithogenic risk factors like calcium, oxalate, phosphorus, citrate, and marker enzymes such as lactate dehydrogenase (LDH) and gamma-glutamyltransferase (gamma-GT) were carried out in the collected urine sample.

RESULTS

Urinary excretion of calcium and oxalate was significantly increased in EG-treated rats. In l-arg supplemented hyperoxaluric rats, these concentrations were significantly (p<0.001) decreased when compared to that of hyperoxaluric rats, and were moderately elevated from that of control rats. The activities of urinary marker enzymes, both LDH and gamma-GT were 2-fold increased in EG-treated rats, when compared to control rats, but these values were maintained near normal in l-arg supplemented EG-treated rats. Citrate excretion was enhanced in the l-arg co-supplemented hyperoxaluric rats. In spectrophotometric crystallization assay system, l-arg supplemented rat THP showed inhibition in nucleation and aggregation phases, whereas EG-treated rat THP showed promotion of both calcium oxalate nucleation and aggregation phases. In calcium-(14)C-oxalate binding assay, THP derived from hyperoxaluric rats exhibited 2-fold increase (p<0.001) in the Ca*Ox binding when compared to control and l-arg supplemented animals.

CONCLUSIONS

l-Arg could act as a potent antilithic agent, by increasing the level of citrate in the hyperoxaluria-induced rats and decreasing calcium oxalate binding to the THP. l-Arg also effectively prevents the deposition of calcium oxalate crystals by curtailing the renal epithelial damage and protein oxidation as evidenced by the normal activities of urinary marker enzymes in l-arg supplemented hyperoxaluric rats.

Successful treatment of hypercalcemia with cinacalcet in renal transplant recipients with persistent hyperparathyroidism

BACKGROUND

Cinacalcet lowers plasma parathyroid hormone (PTH) levels in primary and secondary hyperparathyroidism. The efficacy and safety of cinacalcet have not been examined in renal transplant patients with persistent hyperparathyroidism. The aim of this study was to evaluate the effect of cinacalcet as a novel therapy for the management of such patients.

METHODS

Eleven renal allograft recipients with persistent hyperparathyroidism were treated with cinacalcet. The total study time was 10 weeks. Individual cinacalcet doses were adjusted to obtain a serum calcium in the predefined normal target range of 2.10-2.60 mmol/l.

RESULTS

Serum calcium decreased significantly from 2.73+/-0.05 mmol/l to 2.44+/-0.05 and 2.42+/- 0.04 mmol/l after 2 and 10 weeks of treatment, respectively. All patients reached the target range rapidly and remained normocalcaemic throughout the study. Serum PTH significantly decreased 16.1 and 21.8% at study weeks 2 and 10, respectively, compared with week 0. Serum phosphate increased. Renal function remained stable and no allograft rejection was observed. From weeks 2 to 10, daily cinacalcet doses administered were 30 mg (n = 8), 15 mg (n = 1) and 60 mg (n = 1), respectively.

CONCLUSION

Cinacalcet was effective in correcting the hypercalcaemia associated with persistent hyperparathyroidism after renal transplantation. It appears to be safe. Thus, cinacalcet represents a promising alternative for parathyroidectomy in these patients.

Ethnic background has minimal impact on the etiology of nephrolithiasis

PURPOSE

Nephrolithiasis disproportionately affects white patients. However, recent studies propose an increase in the incidence of stone disease in nonwhite populations. We compared the metabolic risk factors of ethnically disparate stone formers from the same geographic region.

MATERIALS AND METHODS

A retrospective review of 1,141 patients identified 98 (9%) nonwhite stone formers. Of these individuals 60 underwent a comprehensive metabolic evaluation, comprising 44 black, 8 Asian and 8 Hispanic patients. A similar sex and age matched group of 66 white stone forming patients were also identified for comparative analysis. Stone analyses were recorded when available. Urinary metabolic abnormalities were defined as low urine volume-urine volume less than 2,000 cc, gouty diathesis-pH 5.5 or less (normal level 5.5 to 6.5), hypercalciuria-calcium greater than 200 mg, hyperoxaluria-oxalate greater than 45 mg, hyperuricosuria-uric acid greater than 600 mg, hypocitraturia-citrate less than 600 mg and purine gluttony-sulfate greater than 20 mg.

RESULTS

The incidence of metabolic abnormalities was surprisingly similar between the white and nonwhite stone formers. Whites have a higher prevalence of hypercalciuria compared with nonwhites (67% vs 25%, respectively, p <0.01). This comparison persisted when the white group was compared with individual ethnic groups (25% in each group). Whites also displayed a higher mean urinary calcium level (233 mg) than their nonwhite counterparts overall (146 mg), specifically with respect to blacks (146 mg, p <0.01). Asians had higher urine volumes with respect to whites and blacks (p <0.01) and, therefore, a decreased prevalence of low urine volumes (37.5% vs 74.2% and 79.5%, respectively). Hypocitraturia, hyperuricosuria, hyperoxaluria, gouty diathesis and high sulfate levels were equally represented among all ethnic groups.

CONCLUSIONS

Although there appears to be a predominance of stone disease among whites, all racial groups demonstrated a remarkable similarity in the incidence of underlying metabolic abnormalities. These results suggest that dietary and environmental factors may be as important as ethnicity in the etiology of stone disease.

Serial crystalluria determination and the risk of recurrence in calcium stone formers

BACKGROUND

Urinary crystal precipitation is the necessary initial step in kidney stone formation. However, clinical relevance of crystalluria in the evaluation of stone formers is disputed.

METHODS

We serially determined crystalluria in first-voided morning urine samples, together with full 24-hour urine biochemistry, in 181 patients with idiopathic calcium nephrolithiasis who had formed at least one calcium-oxalate stone and were followed for at least 3 years under our care. All stone events which occurred prior to referral, then after entry in the study were recorded.

RESULTS

As compared with 109 patients who had no evidence of stone recurrence during follow-up, the 72 patients who experienced >/= one recurrent stone event had a lower daily urine volume (1.74 +/- 0.06 vs. 2.26 +/- 0.05 L/day (mean +/- SEM) (P < 0.0001), higher urine calcium and oxalate concentrations, and daily calcium excretion, and they had more frequent crystalluria (68% vs. 23% of urine samples) (P < 0.0001). By multivariate Cox regression analysis, the hazard ratio for stone recurrence was 0.32 (95% CI 0.16-0.62) for 1 L increase in daily urine volume, 1.12 (1.09-1.24) for 1 mmol/L increase in urine calcium concentration, 1.24 (1.02-1.50) for 0.1 mmol/L increase in urine oxalate concentration and 27.8 (10.2-75.6) for crystalluria index.

CONCLUSION

These data provide evidence that crystalluria, when repeatedly found in early morning urine samples, is highly predictive of the risk of stone recurrence in calcium stone formers. Serial search for crystalluria, a simple and cheap method, may be proposed as a useful tool for the monitoring of calcium stone formers, in addition to urine biochemistry.

Determination of the calcium oxalate crystallization risk from urine samples: the BONN Risk Index in comparison to other risk formulas

PURPOSE

Regular risk evaluation and risk monitoring during stone therapy are recommended measures to ensure reduction of recurrence of crystal formation. This strategy optimizes the patient treatment by a more individual approach and decreases expensive over treatment. We evaluated the BONN Risk Index (BRI) through data actualization and evaluation refinement. The BRI was compared with the most common methods of risk evaluation, namely calculation of relative urinary calcium oxalate (CaOx) supersaturation (RS) and of the urine activity product (AP)CaOx index to estimate the urine AP with respect to CaOx.

MATERIALS AND METHODS

A total of 201, 12 and 24-hour urine samples were collected from 95 healthy volunteers and from 106 CaOx stone formers. Crystallization experiments following the BRI method were performed. RS and APCaOx were calculated from urinalysis. Data were indexed and individually grouped into 8 classes, and frequency distributions were plotted. A calculation scheme for the BRI based estimation of the statistical probability of a clinically healthy person being a (still nondetected) CaOx stone former is provided.

RESULTS

Logarithmically arranged BRI groups from healthy subject and patient data showed Gaussian frequency distributions. Compared with RS and APCaOx BRI allowed optimum distinction between healthy subjects and stone formers. The healthy subject probability of already being a CaOx stone former strongly increased with increasing BRI.

CONCLUSIONS

The BRI for evaluating CaOx crystallization risk allows reliable distinction between healthy subjects and CaOx stone formers. Although RS and APCaOx require much more analytical efforts for determination, their results do not show higher reliability.

Idiopathic calcium oxalate urolithiasis: risk factors and conservative treatment

Idiopathic calcium oxalate urolithiasis is a frequent and recurrent multifactorial disease. This review focuses on urinary and dietary risk factors for this disease and conservative strategies for rectifying them. Dietary oxalate and calcium and their respective urinary excretions have been extensively investigated during the last 10 years. Urinary oxalate has emerged as the most important determinant of calcium oxalate crystallization while the role of urinary calcium has shifted to bone balance and osteoporosis. Dietary calcium restriction increases urinary oxalate and contributes to a negative bone balance. It has therefore been abandoned as a means to reduce the risk of calcium oxalate kidney stone formation. Calcium oxalate kidney stone patients are advised to increase their fluid intake to achieve a urine volume of 2 l or more; the recommended calcium intake is 800-1200 mg/day; high oxalate foods should be restricted; daily protein intake should be between 0.8 and 1 g/kg body weight/day; essential fats should be included; vegetable and fruit (except oxalate-rich vegetables) intake should be increased. The use of calcium supplements has potential benefits but needs to be examined further.

Metabolic risk factors in patients with renal stones in KwaZulu Natal: an inter-racial study (Asian and Whites)

OBJECTIVE

To identify any differences between Whites and Indians in KwaZulu Natal province, South Africa, in the metabolic risk factors which predispose them to urinary stone formation.

PATIENTS AND METHODS

Urinary stone disease is often a manifestation of an underlying metabolic disorder in most patients. Intrinsic and extrinsic factors affect the susceptibility of an individual to develop urinary stones. Although South African-born Indians and Whites in KwaZulu Natal share some of the same extrinsic factors, diet and genetic factors differ between the groups. In a study from April 1999 until April 2001, 140 patients were included who had a radiological diagnosis of renal calculi; they were evaluated metabolically using previously recommended methods.

RESULTS

All the patients had at least one identifiable metabolic risk factor; the prevalence of the common metabolic risk factors was similar in the two groups. The prevalence of complete renal tubular acidosis (type 1) was significantly higher in the Indian patients. The most common metabolic abnormalities were hypomagnesuria and hypocitraturia, followed by low urinary volume. Hypercalciuria was not significant in this population. While Indians had lower urine volumes than Whites, Whites had significantly higher urinary calcium excretion than Indians.

CONCLUSION

There were a few variations in the metabolic risk factors between Indians and Whites, and the differences could be attributed to genetic or dietary habits. The high incidence of renal tubular acidosis in Indian patients could explain the higher prevalence of urinary stone disease in this group than in other racial groups.

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.

Urinary lithogenic and inhibitory factors in preterm neonates receiving either total parenteral nutrition or milk formula

The aim of this study was to evaluate prospectively the influence of nutrition on certain factors which may inhibit or promote nephrocalcinosis in two groups of preterm infants, receiving total parenteral nutrition (TPN) and special preterm milk formula respectively, but not furosemide. A total of 37 preterm infants, 15 on TPN and 22 fed a special preterm formula were studied at the end of the 1st, 2nd and 3rd weeks of life, at which time serum and 8 h urine specimens were collected. High ratios of urinary calcium to urinary creatinine (UCa/cr), urinary oxalate to urinary creatinine (Uox/cr) and urinary calcium to urinary citrate (UCa/cit) indicates an increased risk for nephrocalcinosis while high urinary citrate to urinary creatinine (Ucit/cr) ratio indicates protection. Uox/cr increased significantly (P<0.05) in those infants fed preterm formula, from the end of 2nd week of life and was two-fold higher than in the TPN group of preterm infants (P<0.01). Ucit/cr was higher throughout the study period in the formula fed than in the TPN preterm infants. UCa/cit was five-fold higher (P<0.01) in the TPN group, by the end of the 3rd week. Urinary calcium and magnesium was similar in both groups during the study period. Two of the infants studied (5.4%), one from each group, developed nephrocalcinosis.

CONCLUSION

In preterm neonates on total parenteral nutrition, urinary oxalate -to-creatinine ratio (a potent lithogenic factor) was lower and urinary citrate -to-creatinine ratio (a lithoprotective factor) also lower than in formula fed neonates. The type of feeding (total parenteral nutrition or special preterm milk formula) seems to affect urinary oxalate and citrate but not calcium and magnesium in non-furosemide treated preterm infants during the first 3 weeks of life.

(Patho)physiological implications of the novel epithelial Ca2+ channels TRPV5 and TRPV6

The epithelial Ca(2+) channels TRPV5 and TRPV6 constitute the apical Ca(2+) entry mechanism in active Ca(2+) (re)absorption. These two members of the superfamily of transient receptor potential (TRP) channels were cloned from the vitamin-D-responsive epithelia of kidney and small intestine and subsequently identified in other tissues such as bone, pancreas and prostate. These channels are regulated by vitamin D as exemplified in animal models of vitamin-D-deficiency rickets. In addition, the epithelial Ca(2+) channels might be involved in the multifactorial pathogenesis of disorders ranging from idiopathic hypercalciuria, stone disease and postmenopausal osteoporosis. This review highlights the emerging (patho)physiological implications of these epithelial Ca(2+) channels.

Pathophysiology of hypocitraturic nephrolithiasis

Urinary citrate inhibits calcium stone formation by complexing calcium in a soluble form and by effects on urinary crystals to prevent growth to stones. Low urinary citrate has been recognized for several decades as a contributing factor in some stone forming patients, but recent studies have elucidated the mechanisms and derangements of the renal handling of citrate in various conditions. In addition, oral citrate as an alkalinizing agent can not only increase urinary citrate, but also favorably impact other stone-promoting conditions. This review will focus on the understanding of these concepts.

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.

Reduced crystallization inhibition by urine from women with nephrolithiasis

BACKGROUND

Human urine is known to inhibit growth, aggregation, nucleation, and cell adhesion of calcium oxalate monohydrate (COM) crystals, the main solid phase of human kidney stones. This study tested the hypothesis that low levels of inhibition are present in women with calcium oxalate stones and, therefore, could promote stone production.

METHODS

In 17 stone-forming women and 17 normal women matched in age within five years, inhibition by dialyzed urine proteins of COM growth and aggregation was examined, as well as whole urine upper limits of metastability (ULM) for COM and calcium phosphate (CaP) in relation to the corresponding supersaturation (SS).

RESULTS

Compared to normals, patient urine showed a reduced ULM in relation to SS. In contrast to men, there was no difference in growth inhibition.

CONCLUSIONS

Reduced CaP and CaOx ULM values in relation to SS are a characteristic of female stone formers. This defect could promote stones by facilitating crystal nucleation. Abnormal inhibition may well be a very important cause of human nephrolithiasis.

[Metabolic risk factors in calcium urolithiasis according to gender and age of the patients]

INTRODUCTION

Little information is available on the metabolic changes found in relation to gender and aging in patients with urolithiasis. In this study a comparison has been made of the metabolic profiles in men and women, in different groups of aging, with calcium-containing urinary stones in order to identify possibly significant differences.

MATERIAL AND METHODS

In the past five years, a total of 500 patients with calcium-containing urinary stones, 226 male (45.2%) and 274 female (54.8%), have undergone comprehensive metabolic evaluation. The mean age was 47.4 years, with a range of 20 to 75 years. The patients was included in 3 groups: 151 patients aged 20-39 years, 255 patients aged 40-59 years and 94 patients aged 60-75 years. A comparison has been made of the frequency of metabolic changes, the urinary biochemical parameters and the supersaturation index (AP(CaOx)) between a group of men and a group of women and the different groups of aging. All patients carried out in an identical manner to metabolic diagnosis. The patients with morphologic and functional abnormalities were excluded.

RESULTS

Hyperoxaluria, hyperuricosuria and hypocitraturia were more common in men than in women, whilst in women, hypercalciuria and a low urinary volume were more frequent with respect to men, though the differences in hypercalciuria were not statistically significant. Men excrete higher levels of calcium, phosphate, oxalate, uric acid and magnesium than women. On the other hand, women excrete higher levels of citrate than men. The AP(CaOx) index is significantly higher in men than in women. Hypercalciuria were more common in patients aged < 60 years, and low urinary volume were more frequent in patients aged < 40 years. Patients aged < 60 years excrete higher levels of calcium, phosphate and uric acid. The AP(CaOx) index is significantly higher in patients aged < 60 years.

CONCLUSIONS

Differences were observed between the metabolic profiles of men and women, and in different groups of aging. Men and younger patients afford a metabolic profile of upper lithogenic risk compared with women and older patients; this is consistent with the upper reported prevalence of lithiasis and the upper tendency to recurrence in men and middle-age patients.