Urinary inhibitors of crystallization in hypercalciuric children with hematuria and nephrolithiasis

Evolution of bone mineral density in patients with idiopathic hypercalciuria: a 20-year longitudinal study

BACKGROUND

Several recent studies reported bone mineral density (BMD) reduction in pediatric patients with idiopathic hypercalciuria (IH). This longitudinal study aimed to evaluate BMD evolution in IH patients through three bone densitometry studies conducted over 20 years on average. A second objective was to evaluate urine calcium and citrate excretion during this period.

METHODS

Case notes of 34 patients diagnosed with IH at age 7.9 ± 3, alongside results of two bone densitometry studies, performed at 10.5 ± 2.7 (BMD1) and 14.5 ± 2.7 (BMD2) years of age, were reviewed. Patients underwent a third densitometry study in adulthood (BMD3) aged 28.3 ± 2.9. Mean follow-up duration (time-lapse between BMD1 and BMD3) was 17.7 ± 1.4 years.

RESULTS

Statistically significant differences were found between z-BMD3 (- 0.85 ± 1.10) and z-BMD1 (- 1.47 ± 0.99) (P = 0.001) as well as between z-BMD3 and z-BMD2 (- 1.33 ± 1.20) (P = 0.016). At the end of follow-up, z-BMD3 was superior to z-BMD2 in 23 adult patients (67.6%) and lower in 11 patients (5M, 6F; 32.3%). Both men and women showed increased bone mass over time, although such increases were significant only for women. The gradual decrease observed in calcium/creatinine and citrate/creatinine ratios could be related to improvement in osteoblastic activity and especially reduction in osteoclastic activity.

CONCLUSIONS

In patients with IH, BMD improves, which may be related especially to female sex, increment of body mass, and reduction in bone resorption. Upon reaching adulthood, urine calcium and citrate excretion tend to decrease so lithogenic risk still remains. The cause of the latter is unknown, although it likely relates to changes in bone activity.

The idiopathic hypercalciuria reviewed. Metabolic abnormality or disease?

Idiopathic hypercalciuria (IH) is defined as that clinical situation in which an increase in urinary calcium excretion is observed, in the absence of hypercalcemia and other known causes of hypercalciuria. In recent years, its diagnosis in pediatric age has been more frequent because it has been known that it can debut with very different symptoms, in the absence of kidney stone formation. The discovery of genetic hypercalciuric stone-forming rats has allowed us to glimpse the pathophysiological mechanism of IH since they show many data in common with humans with IH as normal levels of blood calcium, intestinal calcium hyperabsorption, increased bone resorption and a defect in the renal tubular calcium reabsorption. In 1993, it was shown that in these animals there is an increase in the number of vitamin D receptors (VDR) in the intestine, which favors an increase in the functional capacity of calcitriol-VDR complexes that explains the increase in intestinal transport of calcium. The same happens at the bone level producing a greater resorption. In our opinion, IH is a 'metabolic anomaly' or, better, an inheritable constitutive metabolic characteristic. In this sense, what patients with IH would inherit is the availability of having a greater number of VDRs in their cells than those with normal urinary calcium excretion. IH cannot be considered a sensu stricto disease, so pharmacological treatment must be individualized.

Does hydrochlorothiazide prevent recurrent urinary tract infection in children with idiopathic hypercalciuria?

OBJECTIVE

Idiopathic hypercalciuria (IHC) has been recognized as a common disorder in childhood, and is a major factor in the formation of renal stones and urinary tract infections (UTIs). Since hydrochlorothiazide ameliorates hypercalciuria, we assessed its efficacy in preventing recurrent UTIs in hypercalciuric girls.

MATERIALS AND METHODS

This research was a single blind randomized clinical trial. One hundred 1‒12-year-old girls, who were followed in pediatric nephrology outpatient clinics of two referral hospitals in Markazi Province of Iran, were recruited. All patients had IHC and at least two UTIs in 1 year, without any underlying anatomic or functional abnormality of urinary tract. Patients were randomly divided into two equal groups. One group received instructions regarding general preventive measures for UTI and the other group, in addition to these measures, received 1 mg/kg/day hydrochlorothiazide as morning dose. Then recurrence of UTI in the two groups was evaluated.

RESULTS

The mean age was 7.28 ± 1.9 years. In both groups, the incidence of UTI recurrence was 66%.

CONCLUSION

On the basis of these results, we reject the hypothesis that treating hypercalciuria is beneficial in preventing repeated UTIs. The association between UTIs and IHC needs to be more closely studied and attention to eliminating confounding factors is necessary.

Biochemical risk factors for stone formation in a Scottish paediatric hospital population

Background

Renal stones in children, although rare, may be associated with morbidity and renal damage. Scottish children have a different ethnic composition and diet compared with paediatric populations previously studied. Urinary stone promoters include calcium, oxalate and urate. Postulated inhibitors include citrate and glycosaminoglycans (GAGs). We tested the hypothesis that Scottish paediatric stone-formers have higher excretion of urinary stone promoters (calcium/oxalate/urate) and/or lower excretion of stone inhibitors (citrate/GAGs) than children with isolated haematuria and controls.

Methods

In this case-controlled study, we measured creatinine, calcium, oxalate, urate, citrate and GAGs in random urine samples from 24 stone-formers (excluding inherited metabolic disorders), median age 10.2 (range 1.0–17.2) y; 25 patients with isolated haematuria, 6.3 (0.6–13.7) y; and 32 controls, 7.5 (0.8–14.7) y.

Results

Excretion of urinary promoters and inhibitors differed among stone-formers, haematuria and control groups for (median (range)): calcium (0.82 (0.02–2.19), 0.43 (0.08–2.65), 0.31 (0.04–2.12) mmol/mmol creatinine, respectively, P = 0.005), citrate (0.42 (0.13–0.72), 0.33 (0.05–0.84), 0.61 (0.11–1.75) mmol/mmol creatinine, P = 0.001), calcium:citrate ratio (1.68 (0.19–4.81), 1.30 (0.19–9.57), 0.54 (0.10–2.27) mmol/mmol, P < 0.0001) and the promoter:inhibitor ratio (calcium × oxalate)/(citrate × GAGs) (8.3 (1.0–82.5), 4.3 (1.2–69.5), 2.8 (0.3–13.2) mmol/g, P < 0.0001).

Conclusions

Scottish paediatric stone-formers had lower urinary citrate excretion and higher urinary calcium excretion, calcium:citrate ratio and promoter:inhibitor ratio compared with controls. Urinary calcium excretion and promoter:inhibitor ratio was also higher than children with isolated haematuria. Nevertheless, marked overlap between the stone-former and haematuria groups for promoter:inhibitor and calcium:citrate ratios suggests that some patients with isolated haematuria may be at future risk of urolithiasis.

The relationship of magnesium intake to serum and urinary calcium and magnesium levels in Trinidadian stone formers

BACKGROUND

The present study was undertaken to investigate the relationship between the dietary intake of magnesium and the serum and urinary levels of calcium and magnesium in a group of Trinidadian stone formers.

METHODS

A group of 102 confirmed stone formers presenting to urological clinics were interviewed using a questionnaire designed to obtain a semi-quantitative estimate of their oral magnesium intake. Patients were invited to give blood samples for serum calcium and magnesium levels and to provide 24-h urine specimens for the measurement of urinary levels of these minerals, as well as total urinary volumes. A group of 102 controls was subjected to a similar interview and blood and urinary testing. Chi-square tests and Student's t-tests were used to examine group demographic differences. The Mann-Whitney test investigated differences in biochemical indices. Binary logistic regression was used to identify predictors of stone formation.

RESULTS

Blood samples were obtained from 60 patients and 98 controls. Urine samples were returned by 34 patients and 97 controls. Only 10 stones were retrieved from patients. Patients had a significantly lower magnesium intake, but higher median serum and urinary calcium levels, and higher serum calcium to magnesium ratios than controls. Independent variables capable of predicting stone formation included total magnesium intake and serum and urinary calcium levels.

CONCLUSIONS

Increased serum and urinary calcium levels, calcium to magnesium ratios, and a low magnesium intake were predictive of stone formation in this Trinidadian population.

[Evaluation of renal stone disease: metabolic study]

Renal stone formation is a multifactorial process in which all the information obtained from the patient (medical history, imaging tests, stone analysis, metabolic study and physicochemical urine analysis) shows a different facet of the same process. Consequently, all these investigations should be evaluated together. In half of all patients, stone formation is secondary to the presence of metabolic alterations in urine, of which the most frequent is idiopathic hypercalciuria. The second most frequent cause is infection and/or urinary malformations, while hereditary enzyme defects are highly unusual. Reference values for urinary excretion of lithogenic metabolites (calciuria, uricosuria, oxaluria, citraturia, etc.) are essential for an adequate metabolic study, since urinary excretion depends on multiple factors, which have been described in the various publications in the literature. Physicochemical study evaluating saturation of the various salts dissolved in urine should be performed. These saturations are currently considered to be a highly useful index for determining the risk of crystallization and stone formation in patients with lithiasis and for evaluating the effectiveness of treatment. Lastly, the metabolic profile of renal lithiasis in children resembles that in adults, suggesting that predisposition to renal lithiasis begins in childhood. The early detection of the metabolic alterations observed in these patients will reduce the incidence of this disease in both children and adults.

Analysis of calcium, oxalate, and citrate interaction in idiopathic calcium urolithiasis in children

The majority of urinary stones in children are composed of calcium oxalate. To investigate the interaction between urinary calcium, oxalate, and citrate as major risk factors for calcium stones formation, their 24-h urinary excretion was determined in 30 children with urolithiasis and 15 normal healthy children. The cutoff points between children with urolithiasis and healthy children, accuracy, sensitivity, and specificity for each risk factor alone as well as for all three taken together were determined. OneR and J4.8 classifiers as parts of the larger data mining software Weka, based on machine learning algorithms, were used for the determination of the cutoff points for differentiation of the children. The decision tree based on J4.8 classifier analysis of all three risk factors together proved to be the best for differentiating stone formers from normal children. In comparison to the accuracy of the differentiation after calcium and oxalate of 80% and 75.6%, respectively, the decision tree showed an accuracy of 97.8%. Even when its stability was tested by the leave-one-out cross-validation procedure, the accuracy remained at a very acceptable percentage of 93.2% correctly classified patients. J4.8 classifier analysis gave a look inside urinary calcium, oxalate, and citrate interaction. Urinary calcium excretion was shown as the most informative in discrimination of the children with urolithiasis from healthy children. However, it was shown that oxalate and citrate excretions might influence the stone formation in a subpopulation of the stone formers. In patients with low urinary calcium, a major role in lithogenesis belongs to oxalate, in some of them alone and in others in conjunction with citrate. Decreased urinary citrate excretion in the presence of increased oxalate excretion may lead to stone formation.

Value of the urinary stone promoters/inhibitors ratios in the estimation of the risk of urolithiasis

An imbalance between urinary-promoting and -inhibiting factors has been suggested as more important in urinary stone formation than a disturbance of any single substance. To investigate the value of promoter/inhibitor ratios for estimation of the risk of urolithiasis, urinary citrate/calcium, magnesium/calcium oxalate, and oxalate/citrate x glycosaminoglycans ratios were determined in 30 children with urolithiasis, 36 children with isolated hematuria, and 15 healthy control children. The cutoff points between normal children and children with urolithiasis, accuracy, specificity, and sensitivity for each ratio were determined and compared with those of the 24-h urine calcium and oxalate excretion and urine saturation calculated with the computer program EQUIL 2. The neural network application (aiNET Artificial Neural Network, version 1.25) was used for the determination of the cutoff points for the classification of normal children and the urolithiasis group. The best test for differentiating stone formers from non-stone formers proved the aiNET determined cutoff values of oxalate/citrate x glycosaminoglycans ratio. The method showed 97.78% accuracy, 100% sensitivity, and 93.33% specificity. Two cutoff points between normal and urolithiasis groups were found showing that the children with urolithiasis had ratio values either above 34.00 or less than 10.16. Increased oxalate excretion was linked to the first cutoff value (34.00), and decreased glycosaminoglycans excretion was typical of the second cutoff value (10.16).

Determination of urine saturation with computer program EQUIL 2 as a method for estimation of the risk of urolithiasis

To investigate the risk for the development of urolithiasis in 30 children with urolithiasis, 36 children with isolated hematuria, and 15 healthy control children, 24-h urinary excretion of calcium, sodium, oxalate, citrate, sulfate, phosphate, magnesium, urate, chloride, ammonium, and glycosaminoglycans was determined and urine saturation for calcium oxalate was calculated with the computer program EQUIL 2. Compared with controls, children with urolithiasis had significantly increased calcium excretion, oxalate excretion, and urine saturation, whereas children with isolated hematuria had significantly increased calcium excretion only. The best estimation of the relative risk of urolithiasis can be made after urine saturation, using logistic regression. The percentage of patients correctly classified after urine saturation is 85.41% in comparison with 80.95% and 73.81% when the estimation was done by calcium excretion and oxalate excretion, respectively. Using the breakpoint value of 4.29 for urine saturation, it was possible to separate children with increased risk of urolithiasis development from the group of children with isolated hematuria.