Saudi Journal of Kidney Diseases and Transplantation

: 2013  |  Volume : 24  |  Issue : 5  |  Page : 1055--1061

Idiopathic urolithiasis in Tunisian children: A report of 134 cases

A Alaya1, R Sakly2, A Nouri3, MF Najjar4, M Belgith3, R Jouini3,  
1 Department of Biochemistry and Toxicology, University Hospital; Ecole Supérieure des Sciences et Techniques de la Santé de Monastir, Unité de Nutrition et Métaux Lourds, Monastir, Tunisia
2 Ecole Supérieure des Sciences et Techniques de la Santé de Monastir, Unité de Nutrition et Métaux Lourds, Monastir, Tunisia
3 Department of Pediatric Surgery, University Hospital, Monastir, Tunisia
4 Department of Biochemistry and Toxicology, University Hospital, Monastir, Tunisia

Correspondence Address:
A Alaya
Department of Biochemistry and Toxicology, University Hospital, Monastir


We evaluated the metabolic and the nutritional aspects of 134 urolithiasis children in order to outline the characteristics of idiopathic urolithiasis in children. This prospective study group of 134 children (56 females, 78 males) with renal calculi was evaluated. The age range of the patients was six months to 16 years. A dietary survey was performed on every child. All patients were investigated with respect to stone localization and serum and urine risk factors. Statistical analysis of data was carried out using software SPSS 11.0 for Windows. Hypercalciuria was the most common risk factor detected in this group (28.3%). A decrease of water intake was noted in all age groups, especially in the rural area (549.6 mL/day vs. 1150.6 mL/day), and there was an increase in animal protein intake in 17 cases (mean: 1.9 g/kg). In addition, increased intake of starchy foods and food with high oxalate content (sorgum) were detected in the ten to 16 years age group (51%) of our study. Calcium oxalate monohydrate represents the principal component of idiopathic stone (58.2%), which is more frequent in children (68%) than in infants (51.7%) (P <0.02). The major etiology of idiopathic urolithiasis highlights the influence of dietary habit in stone formers in our country. The increased occurrence of calcium oxalate stones in school age children confirms the change in the etiology of urolithiasis according to age.

How to cite this article:
Alaya A, Sakly R, Nouri A, Najjar M F, Belgith M, Jouini R. Idiopathic urolithiasis in Tunisian children: A report of 134 cases.Saudi J Kidney Dis Transpl 2013;24:1055-1061

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Alaya A, Sakly R, Nouri A, Najjar M F, Belgith M, Jouini R. Idiopathic urolithiasis in Tunisian children: A report of 134 cases. Saudi J Kidney Dis Transpl [serial online] 2013 [cited 2022 Jul 1 ];24:1055-1061
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Until now, renal stones in developing countries were considered to be very different from those observed in industrialized countries. [1] Over the last few decades, lifestyle and dietary habits have been westernized in our country. Idiopathic urolithiasis in the upper urinary tract has become by far the most common type of urinary calculi. [2] The changing pattern of urolithiasis in the Tunisian pediatric population has been mentioned in our previous studies. [2],[3] In this study, we evaluated the metabolic and nutritional aspects of 134 children suffering from stone disease in order to outline the risk factors that contribute to idiopathic stone formation in children.

 Patients and Methods

One hundred and thirty-four children aged six months to 16 years with urolithiasis were admitted between 2002 and 2010 to the pediatric surgery department at the University Hospital of Monastir, Tunisia. Epidemiological data as well as mode of onset, underlying disease, imaging and laboratory analysis were recorded. The dietary habits and family backgrounds were obtained from all parents. A dietary survey was performed on every patient to measure actual food intake at the individual level by administering a food frequency questionnaire, recording weights of foods consumed and asking respondents to recall what they frequently ate before the first lithiasic symptom. Clinical examination was performed in all cases, but was incomplete in 24 patients (17.9%).

Normal values for urine constituents were defined as <4 mg/kg for calcium, <0.57 mg/kg for oxalate, <10.7 mg/kg for uric acid and >320 mg/kg for citrate. [4],[5] Interpretation was based on ratios (x over creatinine). Briefly, the upper limits of normal (mol/mL) used for the age groups 1-3/3-5/5-7 and >7 years were for calcium 1.4/1.1/0.8/0.7, for oxalate 0.12/0.08/0.07/0.06 and for uric acid 1.3/1.1/ 0.8/0.55, respectively.

All stones were documented by ultrasound and intravenous urography. All stones were examined by infrared spectroscopy in the laboratory. The structure of each one was established using a stereomicroscope to define the morphology of the stone and to select its parts (nucleus or core, internal section and external surface) in order to determine its molecular and crystalline composition by infrared spectroscopy. A stone component was considered as the main component if it exceeded 70% of the total stone composition.

Statistical analysis of data was performed using SPSS 11.0 for Windows. Mean values and standard deviation were calculated for all groups. Chi-square test was applied to compute the significance of the categorical variables and P <0.05 was considered significant.


Between 2001 and 2009, 205 children suffering from urolithiasis were admitted to our service. One hundred and thirty-four (65.4%) children were classified as idiopathic urolithiasis. Of the 134 children with urolithiasis, 78 (58.2%) were males and 56 (41.8%) were females (sex ratio = 1.47). Children's age at presentation ranged from six months to 16 years (mean age 6.5 years) and 50.7% of the study group were below five years of age. Patients were predominantly from the rural areas (107 patients, 79.8%) of the central coast of Tunisia.

The upper urinary tract was most frequently affected by this pathology (68.6%). Evaluation of the detailed histories provided by the parents revealed a positive family history in 15 patients (12.7%).

Thirty-eight (28.3%) children were associated with hypercalciuria and had urinary calcium/ urinary creatinine more than 0.21 mg/mg (mean: 0.33 mg/mg)". These patients excreted more than 4 mg/kg/day calcium [range: 4.57-8.28 mg/kg/day (mean: 5.20 mg/ kg/day)] without hypercalcemia. Twenty patients (52.6%) in this idiopathic hypercalciuric group had a urinary creatinine concentration higher than the other children (mean 28.4 mg/ kg vs. 15.5 mg/kg, P <0.01), suggesting that these children have lower water intakes.

The urine Na/K ratio (mEq/mEq) was determined in 35 cases, this and ranged between 1.43 and 35.35 (mean 6.97 mEq/mEq), demonstrating a higher sodium intake in 21 cases, ranging from 1 g/day to 8.4 g/day (mean: 7.95 g/day).

Stone analysis showed a predominance of oxalate monohydrate associated with hyperoxaluria. Primary hyperoxaluria was excluded in our analysis (absence of type Ic). According to the morphological study, intermittent hyperoxaluria was suspected to be at the origin of stone building in 54 cases; however, biological analysis showed hyperoxaluria in only eight cases to be associated with whewellite stones that were metabolically active.

Twenty-four-hour urinary citrate assays performed in 20 subjects (14.9%) revealed hypocitraturia in 15 cases (mean citraturia of 106.6 mg/g creatinine) (range: 92.3-113.2 mg/g creatinine). Hypocitraturia was associated with high protein intake in only eight cases (40%). The dietary habits of the children with idiopathic urolithiasis were thoroughly investigated [Table 1] and [Table 2]. The evaluation of the content of the foods consumed demonstrated decreased water intake in all age groups, especially in the rural area (549.6 mL/day vs. 1150.6 mL/day), and increase in animal protein intake in 17 cases ranging from 1.4 g/kg to 2.4 g/kg (mean: 1.9 g/kg). Additionally, increased intake of starchy foods and food with high oxalate content (sorgum) was detected in the ten to 16 years age group (51%) of our study.{Table 1}{Table 2}

Calcium oxalate monohydrate represents the principal component of idiopathic stone (58.2%) [Table 3], which was more frequent in children (68%) than in infants (51.7%) (P <0.02) [Table 4]. The microscopic stone analysis has shown the prevalence of whewellite type Ia, with the absence of whewellite type Ic.{Table 3}{Table 4}


Urolithiasis has become more common in children over the past few decades probably as a result of rapid variations in dietary habits and increasing affluence. The change of socio-economic conditions has generated changes in the frequency and type of urolithiasis in terms of both site and physicochemical composition of the calculi. [6]

Stones appear to be particularly common in children living in Tunisia, and this study is one of the largest reported on urolithiasis in the pediatric age group of this country. [2],[3],[7],[8] Stone composition has changed substantially over the past decades in Tunisia, with a progressive increase in frequency of calcium oxalate stones. [2] This is seen even in the eastern hemisphere, where these stones have been traditionally less frequent than uric acid- and infection-associated stones. Recent epidemiology studies from different continents and countries report that calcium oxalate accounts for 60-90% of stones in children. [9],[10],[11],[12],[13],[14],[15],[16],[17]

Idiopathic urolithiasis in children has become frequent in the western world as a result of the changes in dietary habits in the last few decades. [18] There is a wide variation in the prevalence of idiopathic urolithiasis in different countries. The lowest prevalence is reported from Japan (0.6%), [19] whereas this prevalence is striking in Germany (8.6%), [20] Italy (9.1%), [21] USA (12-13%), [22],[23] Turkey (2.9%) [26] and Argentina (12.7%). [24] In our study, idiopathic urolithiasis was observed in 65.4% of the cases.

Hypercalciuria is the most common etiology of urolithiasis in children and adults. [25],[26],[27],[28],[29] Idiopathic hypercalciuria was observed in 41.8% of our study population. It was postulated that the hot climate in such geographical areas contributes to dehydration and, hence, decreased urinary volume, increased urine osmolarity and increased concentration of calcium and oxalate. [30],[31] The climate in our region is so hot that the maximum temperature exceeds 35-40°C on most days between June and September, resembling the climate of the Arabian Peninsula. In addition, the majority of patients with idiopathic stone resides in rural areas where water intake in children does not exceed 549.6 mL/ day. A low water intake was more obvious in patients with idiopathic hypercalciuria than in the other etiologic group.

Since 1986, the frequency of occurrence of kidney stone has been on a continuous rise in Tunisia. [2] Increase in upper urinary tract stone prevalence also occurred in eastern countries, where consumption of animal and vegetable proteins has considerably increased during the past few decades. [32],[33] Epidemiologic observations leave no doubt that diet plays a major, if not the most important, role in the pathogenesis of urolithiasis. [6]

Several previous studies have demonstrated the role of diet on hypercalciuria and augmented oxalate excretion. [34],[35],[36],[37],[38] Increased protein and salt intake and decreased potassium intake were commonly observed in urolithiasic children in the Western society. [37],[39],[40] Since the 60s, dietary habits have been dramatically westernized in Tunisia. [41],[42] An increase in meat and milk intake was noted whereas the cereal intake decreased. [43] In our study, patients showed an increased animal protein intake in teenage children.

Calcium oxalate stone linked to dietary habits is frequent among adults than among children. [7],[43] The relationship between frequency of main types of stones and patients' age was previously reported by Daudon et al. [44] This reflects both nutritional change and metabolism evolution depending on the patient's age. These data were widely noted in adults, [44],[45] specifically for the two forms of calcium oxalate: The whewellite (calcium oxalate monohydrate) and weddellite (calcium oxalate dihydrate). The high frequency of the whewellite form among teenage children in our study confirms the role of food-borne hyperoxaluria in developing these stones. Indeed, the dietary survey revealed an excessive consumption of chocolate and sorghum in more than half of the patients in this age group.

The ingestion of proteins has other effects on urine chemistries. Lowering of citrate excretion is the most remarkable one. [46] Hypocitraturia is one of the principal factors promoting stone formation in idiopathic stone disease, with a prevalence ranging from 8% up to 68.3%. [47] Hypocitraturia was found in 15 children, and was associated with high protein intake in only eight children. A low citrate output in stone formers may also be linked to renal defects (impairment of the sodium citrate cotransport or alteration of intracellular citrate regulation), inappropriate intestinal citrate or alkali absorption [47] or low magnesium or potassium levels. [48]

The prevalence of uric acid stone also appeared to be influenced by animal protein in the diet. [6] These data were not confirmed by our results. However, the most remarkable change in purine stones was the disappearance of uric acid anhydrous in older children. Metabolic (genetic or acquired) disorder can be considered to explain this change. However, we believe that tubular immaturity in infants associated with a lack of reabsorption of uric acid is the main reason in this case. [49]

The epidemiology of renal stones is continuing to change in our country toward a predominance of calcium oxalate stones, probably highlighting the influence of dietary habits in stone formers. The increase in calcium oxalate stones in school age children confirms the change in the etiology of urolithiasis according to age.


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