Urinary metabolic evaluations in solitary and recurrent stone forming children. J Urol. 2008;179:2369-2372. [PMID: 18433777 DOI: 10.1016/j.juro.2008.01.151]

Enteral nutrition and the risk of nephrolithiasis in complex pediatric patients

PURPOSE

Medically complex, non-ambulatory children can often suffer from nephrolithiasis. The purpose of this study is to determine risk factors which are predictive for recurrent stone formation in this patient population.

MATERIAL AND METHODS

A retrospective cohort study was performed on non-ambulatory patients with cerebral palsy and/or severe developmental delay presenting to a high-volume Pediatric Stone Center from 2015 to 2019. Two 24-hour urine collections were performed as a baseline prior to pharmacotherapeutic and/or dietary intervention. Healthy stone-forming children served as a control group.

RESULTS

28 non-ambulatory subjects and 38 healthy controls were evaluated. The study group had a higher rate of bilateral nephrolithiasis but a similar history of previous surgical procedures. 89% of the non-ambulatory children were fed via a gastrostomy. The median calcium excretion was the same in both groups (3.0 mg/kg/day). The median 24-hour excretion of oxalate was significantly increased in the study group (54 vs 31 mg/1.73 m²/day, p = 0.0001). Urinary citrate and phosphorus excretions, and the supersaturations of calcium oxalate and calcium phosphate were similar between study subjects and controls. Calcium oxalate stones were noted in 57% of those with known stone composition in the study group. Enteral feeding formulas were primarily based on soy protein, a known high oxalate food.

CONCLUSIONS

Urinary oxalate excretion is significantly increased in a cohort of medically complex, non-ambulatory stone-forming children. Urinary calcium excretion was not elevated between study subjects and healthy controls. Further analysis is needed to assess if dietary intervention to limit oxalate excretion results in decreased stone formation.

Analysis of urine composition from split 24-h samples: use of 12-h overnight samples to evaluate risk factors for calcium stones in healthy and stone-forming children

INTRODUCTION

The analysis of 24-h urine is the gold standard to diagnose metabolic abnormalities in the stone-forming patient. However, urinary composition changes throughout the day and analyzing the whole 24-h urine may mask peaks of increased risk of crystallization.

OBJECTIVE

To examine variations of stone-promoting and stone-inhibiting factors in urine using split 24-h samples from healthy and stone-forming children.

STUDY DESIGN

Urine was collected from 87 healthy and 26 stone-forming children using a split collection procedure (12-h daytime urine and 12-h overnight urine). Urine volume, pH, calcium (Ca), magnesium (Mg), phosphate (P), citrate (Cit), uric acid (Ur), and oxalate (Ox) were determined, and the Ca/Cit ratio was calculated.

RESULTS

The overnight urine samples in both groups had higher levels of P and Mg, lower volume, lower pH, and less citrate and uric acid. As can be seen in the table, higher percentages of healthy and stone-forming children had altered 12-h night urine than 24-h urine with regards to Ca/Cr, Cit/Cr and Ca/Cit ratios. All healthy subjects and all stone-forming children (except one) with altered Cit/Cr ratios or Ca/Cit ratios in the 24-h sample also had altered ratios in the 12-h overnight sample.

DISCUSSION

This study indicates that urine composition changes throughout the day, and that there is daily variability in most of the parameters related to kidney stone formation. Furthermore, 12-h overnight samples seem to be more sensitive than 24-h samples in detecting the most common urinary abnormalities. The main limitation of this study is the relative low sample size of stone-forming children, owing to the low prevalence of nephrolithiasis in childhood.

CONCLUSIONS

We observed a higher excretion of stone-promoting substances and a lower citrate in urine at night. However, the study results do not provide enough evidence to conclude that the use of a 12-h overnight sample collection can replace 24 h urine analysis in the metabolic evaluation of children with lithiasis.

Stone recurrence among childhood kidney stone formers: results of a nationwide study in Iceland

OBJECTIVES

To examine the stone recurrence rate among childhood kidney stone formers in the Icelandic population.

MATERIALS AND METHODS

We retrospectively examined kidney stone recurrence in a recently reported population-based sample of 190 individuals who experienced their first stone before 18 years of age in the period 1985-2013. Of these 190 individuals, 112 (59%) were females and the median (range) age at the incident stone diagnosis was 15.0 (0.2-17.9) years. Stone recurrence was defined as an acute symptomatic episode with imaging confirmation or self-reported stone passage, new stone detected by imaging in asymptomatic patients, and suspected clinical stone episode without verification. The Kaplan-Meier method was used to assess stone-free survival and the Chi-square, Fisher's exact, Wilcoxon rank-sum and the log-rank tests to compare groups.

RESULTS

A total of 68 (35%) individuals experienced a second stone event, 1.7 (0.9-18.9) years after the initial diagnosis. The recurrence rate was 26%, 35%, 41% and 46% after 5, 10, 15 and 20 years of follow-up, respectively. The 5-year recurrence rate increased with time and was 9%, 24% and 37% in the periods 1985-1994, 1995-2004 and 2005-2013, respectively (P = 0.005). No difference in stone recurrence was observed between the sexes (P = 0.23).

CONCLUSIONS

In our population-based sample of childhood kidney stone formers, the stone recurrence rate is similar to that reported for adults. The observed rise in stone recurrence with time may be related to closer patient follow-up in recent years or increased stone risk in general.

Association Between Daily Water Intake and 24-hour Urine Volume Among Adolescents With Kidney Stones

OBJECTIVE

To determine the association between daily water intake and 24-hour urine volume among adolescents with nephrolithiasis in order to estimate a "fluid prescription," the additional water intake needed to increase urine volume to a target goal.

METHODS

We conducted a secondary analysis of an ecological momentary assessment study that prospectively measured daily water intake of 25 adolescents with nephrolithiasis over 7 days. We identified 24-hour urine volumes obtained for clinical care within 12 months of water intake assessment. A linear regression model was fit to estimate the magnitude of the association between daily water intake and 24-hour urine volume, adjusting for age, sex, race, and daily temperature.

RESULTS

Twenty-two participants completed fifty-seven 24-hour urine collections within 12 months of the study period. Median daily water intake was 1.4 L (IQR 0.67-1.94). Median 24-hour urine volume was 2.01 L (IQR 1.20-2.73). A 1 L increase in daily water intake was associated with a 710 mL increase in 24-hour urine output (95%CI 0.55-0.87). Using the model output, the equation was generated to estimate the additional fluid intake needed fluid prescription (FP) to produce the desired increase in urine output (dUOP): FP = dUOP/0.71.

CONCLUSION

The FP equation (FP = dUOP)/0.71), which reflects the relationship between water intake and urine volume, could be used to help adolescents with nephrolithiasis achieve urine output goals to decrease stone recurrence.

CLINICAL-EPIDEMIOLOGICAL PROFILE OF 106 PEDIATRIC PACIENTS WITH UROLITHIASIS IN RIO DE JANEIRO, BRAZIL

Objective:

To describe the frequency, clinical profile and treatment of patients with urolithiasis in the Pediatric Nephrology Department of a public state hospital in Rio de Janeiro, Brazil.

Methods:

Retrospective study. Data from pediatric patients (age: 1 month - 18 years) with urolithiasis admitted between January/2012 and December/2014 were reviewed from hospital charts. The studied variables were: demographic and anthropometric data, clinical status, family history of urolithiasis, urinary tract infection and use of lithogenic drugs, diagnostic procedures, associated abnormalities, metabolic disorders, treatment and recurrence.

Results:

The frequency of urolithiasis was 13.6%. Main characteristics of the patients: male gender, white race, eutrophy, aged between 5 and 10 years, family history of urolithiasis, previous urinary infection and spontaneous stone passage. Abdominal and flank pain and macroscopic hematuria were the most common complaints. The most frequent metabolic disorders were hypercalciuria, hyperuricosuria and hypocitraturia. Hypocitraturia was associated with previous urinary infection (p=0.004). Abdomen/urinary tract ultrasonography was the most commonly used diagnostic test. Hydronephrosis occurred in 54.4% of the cases, 81.1% of the stones were in the kidneys, and bilateral stones were associated to a family history of urolithiasis (p=0.030). Recurrence rate was 29.3% (most patients had a metabolic disorder). In 12.3%, the patients underwent lithotripsy, 24.5% were surgically treated (mainly pyelolithotomy), and only 7.6% had their stones analyzed (calcium oxalate was the main finding in the examined stones).

Conclusions:

The frequency of urolithiasis in these pediatric patients was similar to that reported by the literature. A metabolic evaluation is required and the composition of stones should be better evaluated.

The ability of a limited metabolic assessment to identify pediatric stone formers with metabolic abnormalities

INTRODUCTION

American Urological Association guidelines recommend a urinary metabolic evaluation after the first stone event in all pediatric stone patients. Prior studies identified hypercalciuria and urine hypovolemia as the most common abnormalities in children with urolithiasis. Recent data suggest that hypocitraturia is most prevalent. It was hypothesized that a limited evaluation would detect the majority of clinically significant metabolic abnormalities in pediatric stone formers.

MATERIAL AND METHODS

A retrospective analysis of all children (<18 years of age) with renal/ureteral calculi evaluated at the study institution from 2005 to 2015 was performed. Children with ≥ one 24-h urinary metabolic profile after a clinical visit for renal/ureteral calculi were included. Those with bladder stones and those with undercollection or overcollection or missing urinary creatinine were excluded. Demographics and data from the first urinary metabolic profile and stone analyses were collected. The sensitivity, specificity, and positive and negative predictive value (NPV) of a limited urinary metabolic evaluation consisting of four parameters (24-h calcium, citrate, and oxalate and low urinary volume) were compared to a complete urinary metabolic profile. The number and type of metabolic abnormalities that would have been missed with this limited evaluation weredetermined.

RESULTS

Of 410 patients, 21 were excluded for age ≥18 years, 13 for bladder stones, 248 for overcollections, 38 for undercollections, and 10 for missing creatinine. This left 80 patients for inclusion: median age 11.4 years, 60% female, and 96.3% white. Of the entire cohort, 69.6% had hypocitraturia, 52.5% had low urine volume, and 22.5% had hypercalciuria. Sensitivity was 87.5%. Specificity could not be calculated because no patients had a normal complete metabolic evaluation. The NPV was zero, and the positive predictive value was 100%, but these are artifacts resulting from the absence of patients with a normal complete metabolic evaluation. Of the 80 patients, 10 had at least one abnormality missed by a limited metabolic evaluation (Table 1). The missed abnormalities were high pH (n = 6), abnormal 24-h phosphorus (low in 1 patient and high in 1 patient), low 24-h magnesium (n = 3), low 24-h potassium (n = 3), and high 24-h sodium (n = 4).

DISCUSSION

A limited urinary metabolic evaluation would have detected the vast majority of clinically significant metabolic abnormalities in the study sample. Approximately two-thirds of the study patients submitted inadequate 24-h urine specimens.

CONCLUSIONS

A simplified approach to metabolic evaluation in first-time stone formers with a stone analysis available was proposed. This streamlined approach could simplify the metabolic evaluation and reduce health care costs.

24 Hour urine metabolic differences between solitary and multiple stone formers: Results of the Collaboration on Urolithiasis in Pediatrics (CUP) working group

INTRODUCTION

Specific factors associated with the risk of developing pediatric urinary stone disease remain unclear, especially those that may be associated with recurrent stone disease.

OBJECTIVE

We compared the results of 24-h urine collections in children with a solitary stone episode to those with multiple stone episodes to determine if there is a difference that may be associated with multiple stone formation in children.

STUDY DESIGN

A multi-institutional retrospective analysis was completed to assess 24-h urinary metabolic profiles in children with urolithiasis aged 2-18 years old. Differences in mean urine collections between the two groups were assessed using chi-square tests to test the associations among gender, stone type, and multiple stone status, as well as multivariate analyses using general linear models.

RESULTS

We analyzed 142 solitary stone patients and 136 multiple stone patients from four centers were included. Multiple stone patients were older than solitary stone patients (mean 13.4 ± 3.6 years vs. 12 ± 3.9 years, p = 0.002). Females were more likely to have multiple stones (58% vs. 39%, p = 0.002). BMI was not associated with multiple stones (p = 0.8467). Multiple stone formers had lower urine volumes, although this did not reach statistical significance when compared with solitary stone formation (20.4 mL/kg/day ± 11.5 vs. 22.9 ± 13.0, p = 0.0880). Higher values for super-saturation of calcium oxalate were associated with multiple stone disease in univariate (p = 0.0485) and multivariate analysis (p = 0.0469) (Figure). Centers located in the Southeast of the United States saw a higher proportion of children with multiple stones (Tennessee 62.7%, Virginia 44.4%, Oregon 31.6%, Michigan 27.3%, p < 0.0001).

DISCUSSION

In a large multi-institutional retrospective analysis we found that multiple stone disease was associated with higher super-saturations of calcium oxalate. Many urinary parameters changed with patient age, highlighting that the values should be interpreted with respect to patient age. The inability to comment on follow-up because of the nature of our dataset is a limitation of this study.

CONCLUSION

Multiple stone disease in children is associated with higher super-saturation calcium oxalate, while lower urinary volume may also be associated with multiple stones; however, further study is required. Early metabolic evaluation may help risk stratify children likely to form multiple stones.

Co-Occurrence of Asthma and Nephrolithiasis in Children

It has been proposed that epithelial dysfunction and inflammation may predispose patients to kidney stone formation. Asthma is another chronic condition related to epithelial dysfunction and inflammation. We hypothesized that pediatric patients with asthma would have an increased prevalence of nephrolithiasis. Furthermore, we investigated if asthma patients with nephrolithiasis have clinical characteristics and urine profiles that point to mechanisms of stone formation. We evaluated 865 pediatric patients who had a diagnosis of nephrolithiasis. Clinical/demographic data and 24 hour urine samples were compared between asthma + stone (n = 142) and stone only patients. Data from asthmatics without stone were also available for evaluation of medication differences among asthma + stone and asthma only patients. The prevalence of nephrolithiasis in the pediatric population at our institution was 0.08% vs. 0.31% in our pediatric asthmatic population. The prevalence of asthma in our pediatric population was 6.8% vs. 26.7% in our pediatric stone patients. Asthma + stone patients were more likely to be on a combination inhaled corticosteroid + long acting beta agonist inhaler as compared to age/gender/BMI matched asthma patients without stone (29.7% vs. 13.7%, p = 0.0012). 259 kidney stone patients had 24 hour urine samples for comparison. There was no difference in 24 hour urine profiles between asthma + stone and stone only patients. Children with asthma have a 4-fold greater prevalence of kidney stones than the general pediatric population. Similarly, children with kidney stones have a 4-fold greater prevalence of asthma. This correlation may suggest a mechanistic link between asthma and nephrolithiasis. Further investigation is needed to elucidate the pathophysiologic origin of this relationship.

Pediatric primary urolithiasis: Symptoms, medical management and prevention strategies

In the past few decades pediatric urolithiasis has become more frequent. The reason for this increase is not completely clear but has been attributed to changes in climate, nutritional habits and possibly other environmental factors. Although less frequent than adult stone disease, urolithiasis in the pediatric age group is also related to significant morbidity, particularly since stones tend to recur, and, thus, should not be underestimated. Most children with idiopathic stone disease have an underlying metabolic abnormality substantiating the importance of metabolic evaluation already following initial diagnosis of urolithiasis. Identification of the metabolic abnormality allows for more specific prescription of non pharmacological and pharmacological interventions aimed at preventing recurrent stone formation. A better understanding of the causes of kidney stone disease will provide better strategies for stone prevention in children.

Evaluation and medical management of kidney stones in children

PURPOSE

We review the current literature on the diagnostic evaluation and dietary and pharmacological management of children with nephrolithiasis.

MATERIALS AND METHODS

We searched MEDLINE(®), Embase(®) and the Cochrane Library from their inceptions to March 2014 for published articles in English on kidney stones and therapy in children 0 to 18 years old. Based on review of the titles and abstracts, 110 of the 1,014 articles (11%) were potentially relevant to the diagnostic evaluation and medical management of nephrolithiasis in children. We summarized this literature and drew on studies performed in adult populations to augment areas in which no studies of sufficient quality have been performed in children, and to highlight areas in need of research.

RESULTS

During the last 25 years the incidence of nephrolithiasis in children has increased by approximately 6% to 10% annually and is now 50 per 100,000 adolescents. Kidney stones that form during childhood have a similar composition to those that form in adulthood. Approximately 75% to 80% of stones are composed of predominantly calcium oxalate, 5% to 10% are predominantly calcium phosphate, 10% to 20% are struvite and 5% are pure uric acid. The recurrence rate of nephrolithiasis in patients with stones that form during childhood is poorly defined. Ultrasound should be used as the initial imaging study to evaluate children with suspected nephrolithiasis, with noncontrast computerized tomography reserved for those in whom ultrasound is nondiagnostic and the suspicion of nephrolithiasis remains high. Current treatment strategies for children with kidney stone disease are based largely on extrapolation of studies performed in adult stone formers and single institution cohort or case series studies of children. Tamsulosin likely increases the spontaneous passage of ureteral stones in children. Increased water intake and reduction of salt consumption should be recommended for all children with a history of kidney stones. Potassium citrate is a potentially effective medication for children with calcium oxalate stones and concomitant hypocitraturia, as well as children with uric acid stones. However, long-term compliance with therapy and the effect on decreasing stone recurrence in children are unknown. Based largely on efficacy in adult populations, thiazide diuretics should be considered in the treatment of children with calcium based stones and persistent hypercalciuria refractory to reductions in salt intake.

CONCLUSIONS

The incidence of kidney stone disease in children is increasing, yet few randomized clinical trials or high quality observational studies have assessed whether dietary or pharmacological interventions decrease the recurrence of kidney stones in children. Collaborative efforts and randomized clinical trials are needed to determine the efficacy and effectiveness of alternative treatments for children with nephrolithiasis, particularly those with calcium oxalate stones and concomitant hypercalciuria and hypocitraturia. Additional areas in need of study are the optimal length of time for a trial of stone passage in children, the cost-effectiveness of medical expulsive therapy vs analgesics alone, and the size and location of stones for which medical expulsive therapy is most effective.

American and Brazilian Children With Primary Urolithiasis: Similarities and Disparities

Objectives. Considering the differences in location, socioeconomic background, and cultural background, the aim of this study was to try to identify possible factors associated with the increased incidence of urolithiasis by comparing American and Brazilian children with stones. Methods. Data of 222 American and 190 Brazilian children with urolithiasis were reviewed including age, gender, body mass index, imaging technique used (ultrasound and computed tomography), and 24-hour urine volume and chemistries. Results. There were no differences between age and gender at diagnosis. Brazilian children were leaner but in no population did obesity rate exceed that of the general population. Ultrasound was most commonly used to diagnose stones, even more so in Brazilians. Decreased urine flow was more common among Americans (P = .004), hypercalciuria among Brazilians (P = .001), and elevated Ca/citrate ratio among Americans (P = .009). There were no differences between the groups in the frequency of hypocitraturia, hyperuricosuria, absorptive hyperoxaluria, and cystinuria. Conclusions. Despite some differences between the populations, the leading causes of urolithiasis among both were “oliguria,” hypercalciuria, and high Ca/citrate ratio. In neither country was obesity the reason for the increase in incidence of urolithiasis, nor was the use of computed tomography. The similarities between the 2 populations call for combining efforts in addressing the leading causes of pediatric urolithiasis.

Urinary citrate excretion in healthy children depends on age and gender

BACKGROUND

Hypocitraturia is considered a major risk factor for calcium stone formation. However, there is no widely accepted reference database of urinary citrate excretion in children. The aim of our study was to determine the amount of citrate eliminated in the urine over a 24-h period in a pediatric cohort and to determine an optimal unit reflecting excretion.

METHODS

The study cohort comprised 2,334 healthy boys and girls aged 2-18 years. The levels of urinary citrate were assessed by an enzymatic method in 24-hour urine and expressed in absolute values, as urinary concentration, citrate/creatinine ratio, per kilogram of body weight, in relation to 1.73 m2, and as the calcium/citrate index.

RESULTS

Similar incremental age-related citraturia rates were observed in both male and female subjects until puberty during which time citrate excretion became significantly higher in girls. Urinary citrate adjusted for creatinine and for body weight showed a significantly decreasing trend with increasing age in both sexes. Urinary citrate corrected for body surface was weakly correlated with age. Thus, the assumption of 180 mg/1.73 m2/24 h for males and 250 mg/1.73 m2/24 h for females as lower cut-off values appeared to be reliable from a practical perspective.

CONCLUSIONS

We found distinct sex-dependent differences in citraturia at the start of puberty, with significantly higher values of urinary citrate in girls than in boys. Further prospective studies are warranted to elucidate whether this difference represents a differentiated risk of urolithiasis.

Pediatric urolithiasis: experience from a tertiary referral center

OBJECTIVE

Pediatric urolithiasis can cause significant morbidity and damage to the kidney, or even renal failure. We review our experience of the management of urolithiasis in pediatric patients at a tertiary referral center.

PATIENTS AND METHODS

We reviewed medical records of all children with urolithiasis who were diagnosed and managed at our center from August 2003 to October 2011. Management was planned according to stone burden and location. We noted and statistically analysed data about age, sex, stone burden, clinical features, management, metabolic abnormalities and recurrence.

RESULTS

There were 325 children with 378 stone sites. Age range was 3-17 (mean 8) years. The male to female ratio was 3:1. Most common presentation was abdominal pain in 257 children (79%), and the most common stone site was kidney in 215 (57%). Twenty-four (7%) children (stone burden ≤3 mm) were managed conservatively, while the rest received some form of intervention. Metabolic workup could be done in 154 (47%) children. A metabolic abnormality was seen in 67 (43%) children, normocalcemic hypercalciuria being the most common. Recurrence of urolithiasis was seen in 78 (24%) children after a mean follow-up of 3.2 (1-6) years, and was more common in those who had a metabolic abnormality or in whom small residual fragments were left in situ.

CONCLUSIONS

Availability of smaller instruments has led to safer use of percutaneous endoscopy and ureteroscopy in children, with results comparable to those in adults and an acceptable complication rate. The presence of a metabolic abnormality is quite common and is a cause of recurrence.

Correspondence between Ca²⁺ and calciuria, citrate level and pH of urine in pediatric urolithiasis

BACKGROUND

Hypercalciuria and hypocitraturia are considered the most important risk factors for urolithiasis. Citrate binds to urinary calcium to form a soluble complex which decreases the availability of ionized calcium (Ca(2+)) necessary for calcium oxalate formation and phosphate crystallization. The aims of this study were to assess the Ca(2+) fraction in relation to total calciuria, citraturia and urinary pH and to determine whether urinary Ca(2+) concentration is a helpful biomarker in metabolic evaluation of children with urolithiasis.

METHODS

We collected 24-h urine samples from 123 stone-forming children and adolescents with hypocitraturia and from 424 healthy controls. Total calciuria (total calcium, Catotal), Ca(2+), pH, citrate, oxalate and Bonn Risk Index (BRI) were assessed and compared between the two groups.

RESULTS

Total calciuria and Ca(2+) content were higher in stone-formers than in the healthy children. In both stone-formers and controls, Ca(2+) content was inversely related to citraturia and urinary pH, whereas the Ca(2+)/Catotal ratio differed slightly between the groups. A large variability in Ca(2+) level was found across individuals in both groups. The BRI increased with increasing calciuria and urine acidity.

CONCLUSIONS

Compared to controls, stone-formers with hypocitraturia demonstrated a higher urinary Ca(2+) concentration, but this was proportional to calciuria. The large individual variability in urinary Ca(2+) content limits its practical use in metabolic evaluation of children with urolithiasis. However, the Ca/Citrate ratio may be a useful clinical tool in evaluating children with urolithiasis.

Pediatric primary urolithiasis: 12-year experience at a Midwestern Children's Hospital

PURPOSE

Due to environmental and social changes (and possibly obesity) as new risk factors for stone formation in adults and changes in imaging techniques, we assessed whether etiologies of primary pediatric urolithiasis have changed, and if relationships exist between the condition and obesity or imaging technique.

MATERIALS AND METHODS

All pediatric patients with documented primary urolithiasis who underwent serum and 24-hour urine analyses between 1999 and 2010 were evaluated. Age at diagnosis, gender, body mass index and imaging technique were recorded.

RESULTS

Of the 222 patients (48% male) all had normal serum creatinine, electrolytes and minerals. Primary pediatric urolithiasis was diagnosed by ultrasound in 73% of cases and computerized tomography in 27%. Mean ± SD annual incidence of urolithiasis per 1,000 clinic visits increased from 2.4 ± 1.5 in the first half of the study period to 6.2 ± 2.1 in the second half (p <0.005). Mean ± SD age at diagnosis was 11.8 ± 3.8 years and body mass index was 21.7 ± 5.7 (rate of overweight 15%). A total of 140 patients had urine output less than 1.0 ml/kg per hour, with this being the only abnormality in 54. Hypercalciuria was observed in 46% of patients, hypocitraturia in 10% and high calcium-to-citrate ratio in 51%. Mild absorptive hyperoxaluria was noted in 3 patients and hyperuricosuria in 11, with all 14 exhibiting at least 1 additional abnormality. Cystinuria was present in 1 patient. No etiology was identified in 20 patients (9.0%).

CONCLUSIONS

Oliguria and hypercalciuria continue to be the most common etiologies of pediatric primary urolithiasis, followed by hypocitraturia. The recent increase in stone incidence is unlikely due to increased use of computerized tomography. Incidence of obesity was not higher than in the general population. Hyperoxaluria and cystinuria are rare, and thus might not be indicated in the initial analysis.

Pediatric urolithiasis in Taiwan: a nationwide study, 1997-2006

OBJECTIVE

To investigate the prevalence, incidence, associated risk factors, and treatment of pediatric urolithiasis in Taiwan.

METHODS

The present study used a subset of the National Health Insurance Research Database, known as the Longitudinal Health Insurance Database 2005, which contains the data for all paid medical benefit claims from 1997 to 2006 for a subset of 1 million beneficiaries randomly drawn from the population of 22.72 million individuals during any part of the calendar year 2005. Our analysis included the data of all newly diagnosed pediatric patients with an "International Classification of Disease, 9th revision," diagnosis of urolithiasis from 1997 through 2006.

RESULTS

A total of 1679 pediatric subjects who had newly diagnosed urolithiasis without a previous attack were identified from 1997 to 2006 as the study sample. Of the 1679 patients, 808 were boys (48.1%) and 871 were girls (51.9%). The incidence rate of urolithiasis in 2005 was 0.047%. The peak age of pediatric stone occurrence in the study sample was 15-18 years (49.6%). The most common associated disease was urinary tract infection (34.1% of all subjects). The occurrence rate of pediatric urolithiasis correlated significantly with the urbanization level of the residence and geographic area.

CONCLUSION

Using a nationwide, population-based study provides important clinical and epidemiologic information regarding pediatric urolithiasis. Additional studies are warranted to determine the effect of geographic area and urbanization level on the occurrence of pediatric stone disease.

Urine risk factors in children with calcium kidney stones and their siblings

Calcium nephrolithiasis in children is increasing in prevalence and tends to be recurrent. Although children have a lower incidence of nephrolithiasis than adults, its etiology in children is less well understood; hence, treatments targeted for adults may not be optimal in children. To better understand metabolic abnormalities in stone-forming children, we compared chemical measurements and the crystallization properties of 24-h urine collections from 129 stone formers matched to 105 non-stone-forming siblings and 183 normal, healthy children with no family history of stones, all aged 6 to 17 years. The principal risk factor for calcium stone formation was hypercalciuria. Stone formers have strikingly higher calcium excretion along with high supersaturation for calcium oxalate and calcium phosphate, and a reduced distance between the upper limit of metastability and supersaturation for calcium phosphate, indicating increased risk of calcium phosphate crystallization. Other differences in urine chemistry that exist between adult stone formers and normal individuals such as hyperoxaluria, hypocitraturia, abnormal urine pH, and low urine volume were not found in these children. Hence, hypercalciuria and a reduction in the gap between calcium phosphate upper limit of metastability and supersaturation are crucial determinants of stone risk. This highlights the importance of managing hypercalciuria in children with calcium stones.

Medical evaluation and management of urolithiasis

Nephrolithiasis is a highly prevalent condition with a high recurrence rate that has a large impact on the quality of life of those affected. It also poses a great financial burden on society. There have been great advancements in the surgical treatment of stone disease over the past several decades. The evolution of surgical technique appears to have overshadowed the importance of prevention of stone disease despite evidence showing medical therapies significantly decreasing stone recurrence rates. Herein we review the metabolic evaluation of stone formers with the use of specific blood and urine tests. We complete our discussion with a review of the medical management of stone formers providing both general recommendations as well as reviewing focused therapies for specific metabolic abnormalities and medical conditions.

An update on the changing epidemiology and metabolic risk factors in pediatric kidney stone disease

Nephrolithiasis in children is a painful and costly disease that may also have detrimental long-term effects on kidney function. Recent data provide evidence that the incidence of nephrolithiasis in children is rising. Children who are white, female, and adolescent seem to have the highest risk for forming symptomatic kidney stones. Although the reasons for the rising incidence and demographic discrepancies in pediatric nephrolithiasis are not yet clear, recent investigations into urine chemistry provide clues regarding predisposing metabolic risk factors. As more data emerge regarding epidemiologic and metabolic characteristics of pediatric kidney stone formers, we hope to gain a better understanding of the causes of kidney stone disease and, ultimately, provide better strategies for stone prevention in children.

Derivation of a melamine oral reference dose (RfD) and drinking-water total allowable concentration

Due to its high nitrogen content, melamine has been used to adulterate food to increase apparent protein content. In 2008, thousands of Chinese infants consumed reconstituted formula derived from melamine-adulterated milk. Urinary-tract stones (comprised of melamine and uric acid) accumulated in some victims and lead to acute renal failure or death. Premature infants and children (<2 yr) have an increased susceptibility to ingested melamine. Due to incomplete reporting, the human data were inadequate to identify a no-observed-adverse-effect level (NOAEL) for melamine-induced pediatric urolithiasis. Urolithiasis, urinary bladder cystitis, and ulcerations were observed in F344 rats after subchronic or chronic ingestion of melamine at > or =72 mg/kg-d. Bladder epithelial damage was followed by epithelial hyperplasia that progressed to bladder papillomas and carcinomas in male but not female F344 rats or male or female B6C3F1 mice. Short-term assays suggest, at best, weak genotoxic activity, and kinetic data show that melamine is not metabolized. Since reliable exposure information was lacking from the clinical reports, an oral reference dose (RfD) based on urolithiasis in male rats after 13 wk of continuous melamine ingestion was calculated as a 10% benchmark dose (38 mg/kg-d). Incorporation of 10-fold interspecies and intraspecies (for the increased susceptibility of infants) uncertainty factors and a threefold database uncertainty factor (for the lack of immunological, neurological and reproduction toxicity data) yields an oral RfD of 0.13 mg/kg-d. Assuming the 70-kg adult consumes 2 L of drinking water daily, a total allowable concentration of 0.9 mg/L (900 microg/L) was calculated for melamine in drinking water.

Intestinal colonization with Oxalobacter formigenes and its relation to urinary oxalate excretion in pediatric patients with idiopathic calcium urolithiasis

BACKGROUND AND AIM

Oxalobacter formigenes is an intestinal bacterium that utilizes oxalate as the only source of energy. It has been suggested that the lack of colonization with this organism may be a risk factor for calcium oxalate urolithiasis. Because this problem was not investigated in pediatric stone formers, we decided to assess it in our patients.

METHODS

The presence of O. formigenes in stool samples of 76 children and adolescents (aged 4.1-18 years) with idiopathic calcium urolithiasis (36 with chemically confirmed calcium oxalate stones and 40 children with a strong clinical suspicion of this type of urolithiasis) was assessed using PCR method. Simultaneously, urinary oxalate excretion was measured in this group. Fifty healthy, age- and sex-matched subjects served as controls.

RESULTS

O. formigenes was found in 21/76 patients (27.6%). In controls, frequency of colonization was similar (26%). The median 24h urinary oxalate excretion in patients colonized with O. formigenes was significantly lower in comparison with non-colonized patients, 0.319 (range 0.141-0.546) and 0.437 (range 0.198-0.967) mmol/1.73 m(2)/24h, respectively.

CONCLUSIONS

Higher urinary oxalate excretion in children with calcium urolithiasis may be a result of the absence of O. formigenes. The reasons for similarly low intestinal colonization with this bacterium in normal subjects and stone formers remain speculative. Thus, further studies are necessary to clarify this issue.

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.

Pediatric urolithiasis

PURPOSE OF REVIEW

We review the recent literature on pediatric urolithiasis and present up-to-date findings on epidemiology, diagnosis, and medical and surgical management.

RECENT FINDINGS

There are surprisingly few reliable data on pediatric urolithiasis incidence, but widespread anecdotal and single-center reports suggest that more children with stones are being seen. The contamination of Chinese infant formula with melamine caused urolithiasis and other renal problems in hundreds of thousands of infants in the region, underlining the role of environmental factors in urolithiasis. Efforts continue to determine normal metabolic parameters in children, but have been hampered by variations among regions, races, and ethnicities. The Bonn Risk Index may prove to be a useful tool for assessing risk of urolithiasis in children. Children with recurrent urolithiasis are more likely to have detectable metabolic abnormalities. Surgical approaches to urolithiasis in children continue to evolve, with robotic-assisted laparoscopy being perhaps the most significant new technique. Finally, clinicians and radiologists must be aware of the potential for dextranomer/hyaluronic acid (Deflux) implants to mimic distal ureteral stones on computed tomography (CT) scan.

SUMMARY

Pediatric urolithiasis is an expanding field, due in part to the apparent increase in cases. Research continues, seeking to refine the appropriate diagnostic and therapeutic approaches in these unfortunate children.

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.

Pediatric stone disease

Urinary stone disease is less common in children than adults. Although many aspects of pediatric stone disease are similar to that of adults, there are unique concerns regarding the presentation, diagnosis, and management of stone disease in children. We present a review of the increasing prevalence of pediatric stone disease, the diagnostic concerns specific to children, recent results from pediatric series regarding the expectant management and surgical treatment of stones, metabolic evaluation, and current research on the genetics of nephrolithiasis.