title: Orthostatic proteinuria and the spectrum of diurnal variability of urinary protein excretion in healthy children.
abstract: The aim of this study was to characterize the 24-h and diurnal variability of urinary protein excretion and identify the prevalence of orthostatic proteinuria (OP) in healthy children. Upright, supine, and 24-h total urinary protein (UrTP) and creatinine clearance (CrCl) were measured in 91 healthy children ages 6-19 years. Urinary protein and creatinine excretions were calculated and examined by gender, age, Tanner stage, and body mass index (BMI). Orthostatic proteinuria (OP) was defined as a 24-h UrTP >100 mg/m(2) with a normal supine UrTP (<4 mg/m(2)/h). There exists a marked diurnal variability in UrTP. The upright UrTP rate was three to four-times greater than the supine rate. UrTP, adjusted for body surface area, is higher in boys than girls and increases with age and BMI. There is a similar increase in upright CrCl compared with supine. Urinary protein to creatinine ratio (UPcr) is strongly correlated with UrTP. OP is common, being found in 20% of children in this cohort, and is more common in boys and associated with age >10 years and BMI >85%. In children with OP, a first morning UPcr shows a value in the normal range, whereas a random daytime UPcr is elevated. There exists a diurnal variability in urinary protein excretion that is exaggerated in participants with OP. UPcr reliably estimates 24-h UrTP. Using current pediatric criteria, OP is very common, particularly in boys. A normal first morning UPcr ratio indicates that a child with elevated random urinary protein has OP.
authors.affiliation: University of New Mexico School of Medicine, Albuquerque, NM, USA. Jbrandt@salud.unm.edu
authors.forename: John Robert
authors.initials: JR
authors.lastname: Brandt
authors.forename: Aaron
authors.initials: A
authors.lastname: Jacobs
authors.forename: Hengameh H
authors.initials: HH
authors.lastname: Raissy
authors.forename: Franceska Marie
authors.initials: FM
authors.lastname: Kelly
authors.forename: Amy Otten
authors.initials: AO
authors.lastname: Staples
authors.forename: Ellen
authors.initials: E
authors.lastname: Kaufman
authors.forename: Craig Stephen
authors.initials: CS
authors.lastname: Wong
mesh_terms: D000293:Adolescent; D002648:Child; D003404:Creatinine / Q000652:urine; D005260:Female; D006801:Humans; D008297:Male; D011187:Posture / Q000502:physiology*; D011507:Proteinuria / Q000652:urine*; D016482:Urinalysis / Q000379:methods*; D055815:Young Adult
chemical_list: D003404:Creatinine