The diagnosis and treatment of pediatric kidney diseases is based on medical history and physical findings. However, in certain cases, a discrepancy between clinical and pathological findings exists, with patients exhibiting similar clinical symptoms despite different underlying pathological features. Although percutaneous renal biopsy is a widely used medical procedure for the diagnosis of kidney disease in adults, the procedure has not been considered suitable for pediatric patients. However, with recent innovations in technique for kidney localization and biopsy, percutaneous renal biopsy is now regarded to be both safe and advisable for the diagnosis of renal disease in pediatric patients and to inform treatment [1­4]. The indications for renal biopsy vary according to the ethnic and age characteristics of the population studied as well as the geographic location [5].

The aim of our study was to classify results of renal biopsy in pediatric pa tients, based on pathological findings, and to compare the pathological diagnosis to clinical findings.

In this study, we examined the anthropometric characteristics of patients who underwent renal biopsy along with their indications for renal biopsy and common histopathological findings. Our study revealed that the asymptomatic urinary abnormality is the most common clinical diagnosis and IgA nephropathy is the most common primary renal disease.

Renal biopsy in pediatric populations was introduced for diagnosing kidney disease in 1951 and has become a routine procedure in pediatric nephrology [7,8]. Over a 27-year period, 345 children underwent renal biopsy in our hospital and we identified an overall failure rate of renal biopsy of 1.2% (4/345), which is comparable to previously published rates [9,10]. Among our study sample, the male-to-female ratio was 1.8:1, a rate of male predominance that was comparable to previously reported sex-specific differences in prevalence [11]. Printza et al. [12] reported that 48.0% of pediatric patients who underwent renal biopsy were 11-14 years old, with 31.0 % between the ages of 6-10 years. We identified a similar age distribution, with 131 patients (41.2%) between the ages of 11-15 years and 129 (40.5%) between the ages of 6-10 years.

Previous studies have identified idiopathic nephrotic syndrome to the most common indication for renal biopsy [13­16]. In contrast, 53.1% of patients in our study populations underwent renal biopsy to evaluate gross hematuria and/or microscopic hematuria. Since 1998 in South Korea, more than 4 million students have participated in annual large-scale urine screening programs; additionally, many school-children with asymptomatic hematuria and/or proteinuria were detected and their diagnoses confirmed through renal biopsy [17]. In current study, asymptomatic urinary abnormalities were clinically diagnosed before renal biopsy in 114 patients (35.9%), with 89 patients (27.9%) diagnosed as having IgA nephropathy after renal biopsy.

Nephrotic syndrome can be associated with various types of glomerulonephritis and, therefore, an accurate histopathological identification of the glomerular lesion is essential to establishing a correct diagnosis and providing the appropriate treatment. Kim et al. [18] reported that among 52 pediatric patients with nephrotic syndrome, 90.4% were diagnosed with primary nephrotic syndrome and 9.6% with secondary nephrotic syndrome. In our study, primary nephrotic syndrome was identified in 95.1% of cases, with secondary nephrotic syndrome identified in 4.9% of cases. According to Choi et al. [11], minimal change disease (MCD) was identified in 72.7% of all pediatric patients. A similar prevalence of MCD (70.1%) was found in our study. In addition, Keeping in mind the controversy regarding the nature of these IgM deposits [19­21], MCD with mesangial IgM deposit was identified in 16.2% in our study. Microscopic hematuria is present at diagnosis in 20% to 30% of children with MCD but rarely persists; macroscopic hematuria occurs in less than 1% of children with MCD [22]. According to White et al. [23], microscopic hematuria was present in 13.0 % of cases with MCD. In our study, we identified hematuria in 30.8% of cases with MCD. Serum albumin levels usually fall below 2.0 g/dL and may be less than 1.0 g/dL in steroid sensitive nephrotic syndrome [24]. Kim et al. [18] reported that the prevalence of low serum albumin levels <2.5 g/dL was 78.4% in children with nephrotic syndrome. In our study, we found that 59.8% of children with nephrotic syndrome and 75.0% of children with MCD showed low serum albumin <2.5 g/dL. Elevated systolic and diastolic blood pressure are initially present in 5-20% of children with MCD, but hypertension usually does not persist [22]. However, the frequency of hypertension occurring in other types of nephrotic syndrome is as high as 80% [22]. In this study, only 15.7 % of all cases of nephrotic syndrome presented hypertension at diagnosis.

IgA nephropathy is the most prevalent form of glomerulonephritis worldwide. However, according to a large biopsy series, the prevalence of IgA nephropathy is influenced by significant race- and ethnicity-specific variation [6]. In their single center study, Choi et al. [11] reported a prevalence rate of IgA nephropathy of 18.2% in children, a prevalence rate similar to that reported in Japan [25]. However, the prevalence rate of IgA nephropathy in current study was 27.9%, relatively high compared to other studies. The higher prevalence of IgA nephropathy in our study reflects that many school children with asymptomatic urinary abnormalities have been detected through annual mass urinary screening, which started in 1998 in South Korea [17]. This screening program allows us to employ an active approach for evaluating children with persistent hematuria. Actually, the numbers of renal biopsy in our hospital increased annually compared to before 2000.

A majority of children with IgA nephropathy present with gross hematuria. In other patients, microscopic hematuria and/ or proteinuria are the only signs at presentation [26]. Asymptomatic gross hematuria was identified in 61.9% of children with IgA nephropathy in our study and the prevalence of gross hematuria is similar to other studies [27,28]. Although IgA nephropathy does not lead to significant renal damage, progressive renal damage develops in 20-30% of patients about 20 years after disease onset. Clinical parameters indicative of a poor prognosis are massive proteinuria (>1 gm/24 hr), renal insufficiency, and hypertension [29]. The prevalence of massive proteinuria (33.3%) and hypertension (14.2%) in present studied population are similar to that seen in other studies [27,28]. In addition, 23 of 27 patients (85.7%) with massive proteinuria and 7 of 12 patients (58.3%) with hypertension were diagnosed with a grade III or IV of IgA nephropathy. Because only less than 30% patients of IgA nephropathy have been follow-up more than 5 years, we could not identify a significant relationship between the above mentioned 3 clinical parameters and prognosis in children with IgA nephropathy.

In conclusion, the most common clinical diagnosis was asymptomatic urinary abnormalities, followed by nephrotic syndrome and acute glomerulonephritis. Primary glomerular disease is the most common histological finding, with IgA nephropathy being the most common histopathological lesion, followed by MCD. Our study demonstrates the importance of percutaneous renal biopsy in the diagnosis and treatment of pediatric renal diseases.