ORIGINAL ARTICLE Orthostatic proteinuria: an overestimated phenomenon? Zümrüt Arslan 1 & Mustafa Koyun 2 & Hakan Erengin 3 & Halide Akbaş 4 & Gülşah Kaya Aksoy 2 & Elif Çomak 2 & Sema Akman 2 Received: 2 December 2019 /Revised: 26 March 2020 /Accepted: 23 April 2020 # IPNA 2020 Abstract Background Although orthostatic proteinuria (OP) is the most common cause of childhood proteinuria, excluding transient proteinuria, data regarding prevalence and long-term prognosis are limited. We aimed to determine prevalence of OP in healthy schoolchildren evaluating relationships with age, gender and body mass index, and determine follow-up. Methods A total of 1701 healthy children aged 6–15 years were selected using a population-based, stratified, cluster-sampling method; and random urine samples were taken. For proteinuria ≥ 1+ in first urine samples, second and third random samples were taken at least 2 weeks apart to exclude transient proteinuria. For continuing proteinuria after third samples, first morning urine samples were collected. Cases where proteinuria was not detected in first morning urine samples were diagnosed as OP. Results Sixty-four of 1701 children (3.7%) had proteinuria on first random urine samples. After second and third urine samples, proteinuria persisted in only 16 (0.94%). OP was detected in 11 (0.65%). Prevalence of OP tended to decrease with increasing BMI, though not statistically significant. All 7 cases with OP who were re-evaluated later, had no proteinuria 3 years after diagnosis. Conclusions Prevalence of OP in our study was lower than the literature. At least three random urine samples should be taken to exclude transient proteinuria in an asymptomatic child/adolescent before making a diagnosis of OP using first morning urine samples. OP is a benign condition and resolves spontaneously in most cases. Underweight children had a tendency for OP compared with overweight and obese children; however, further studies with larger number of patients are needed. Keywords Proteinuria . Orthostatic proteinuria . Prevalence . Schoolchildren Background Orthostatic proteinuria (OP) is the most common cause of proteinuria in children, excluding transient proteinuria [1]. It has been reported in a limited number of studies that the prev- alence of OP in children and adolescents ranges between 1 and 5% [2–5]. Chandar et al. reported that one-third of the cases evaluated for isolated proteinuria were diagnosed as OP [6]. In some studies, it was reported that OP is more common in thin children [7]than in overweight children [8]. It has a peak in- cidence in adolescents and is rare after 30 years of age [9]. However, studies about the long-term prognosis of OP are not satisfactory. The aim of this study was to determine the prev- alence of OP in healthy elementary and junior high school students (6–15 year-old children) in Antalya city center, Turkey, evaluating its relationship with age and gender and body mass index. We also aimed to determine the follow-up of cases with OP a few years after the diagnosis. Methods This cross-sectional study was carried out between March and April 2015. A total of 61,092 students, aged 6–15 years, with- in 124 elementary and junior high schools located in the Muratpasa district of Antalya city center, constituted our study population. For sample selection, a population-based, * Mustafa Koyun mkoyun@akdeniz.edu.tr 1 School of Medicine, Department of Pediatrics, Akdeniz University, Antalya, Turkey 2 School of Medicine, Department of Pediatrics, Division of Pediatric Nephrology, Akdeniz University, Antalya, Turkey 3 School of Medicine, Department of Public Health, Akdeniz University, Antalya, Turkey 4 School of Medicine, Department of Biochemistry, Akdeniz University,, Antalya, Turkey Pediatric Nephrology https://doi.org/10.1007/s00467-020-04586-4