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1. Introduction
At the end of the 1960s, Peterson et al. determined that quantitative analysis of albumin in urine was useful to detect renal alterations [1]. Since then, albumin levels in urine have been used clinically as a tool to measure kidney failure in patients with diabetes mellitus and hypertension [2,3]. Once the relationship between albuminuria and kidney failure was established, quantification methods were developed to be faster and more precise [4].
At present, albuminuria is known as a renal and cardiovascular predictor not only in diabetic patients, but also in those who are apparently healthy. The reported prevalence in general population is 7.2% [5]. The majority of studies have been conducted in adults, despite the interest in early detection having risen recently due to future effects. In Japan, this method has been used since 1979 to detect kidney diseases in the pediatric population [6]. Other countries, such as Australia, the U.K., Norway, the U.S., and Italy, have also carried out this practice since the mid-1980s [7]. Information on prevalence is limited but is reported as approximately 7% [8]. Another study reported that the median ACR (albumin/creatinine ratio) of the random morning urine specimen for children <10 years was 2.91 vs. 2.28 mg/g (p < 0.001) for children ≥10 years. The median urinary albumin concentration for children <10 years was significantly higher than in children ≥10 years (2.53 vs. 2.09 μg/mL; p = 0.008) [9]. More recently, an Australian study considered 975 children aged 5-18 years. The overall prevalence of albuminuria, as defined by an ACR greater than 30 mg/g, was 12.8% (95% CI 9.9-15.6). In males, the frequency of albuminuria was 10.2% (95% CI 6.1-14.2) and in females, it was 15.5% (95% CI 10.7-20.3) [10].
Orthostatic proteinuria is the most common cause of a positive result of protein (albumin among the various proteins in urine) in pediatric patients (often tall, physically active adolescents). In this circumstance, the detection of isolated proteinuria (in the absence of hematuria) in an asymptomatic individual based on a random specimen during the day must be confirmed by repeating the test (dipstick) on a specimen collected immediately upon patient’s awakening in the morning [11]. In 2010, Brandt et al. characterized the 24-h and diurnal variability of urinary protein excretion and...