Source:

Arslan
Z
,
Koyun
M
,
Erengin
H
, et al
.
Orthostatic proteinuria: an overestimated phenomenon?
Pediatr Nephrol.
2020
; doi:
https://doi.org/10.1007/s00467-020-04586-4

Investigators from Turkey conducted a cross-sectional study to assess the prevalence of orthostatic proteinuria (OP) in school-aged children. Investigators used a population-based, stratified, cluster-sampling method to identify a representative sample of children 6–15 years old who attended an elementary or junior high school in Antalya, Turkey. Children with a chronic disease requiring medication were excluded. Demographics and anthropometric measurements were obtained from participating children at baseline.

Investigators collected random urine samples from child participants at their school. Participants who had ≥1+ proteinuria on their first urine sample provided 2 additional random urine samples at least 2 weeks apart. Those whose proteinuria had resolved by the third sample were diagnosed with transient proteinuria. Among participants whose proteinuria persisted on the third sample, a first morning urine sample was obtained. Those with no proteinuria on this first morning urine sample were diagnosed with OP. Those whose proteinuria persisted on the first morning urine sample were diagnosed with persistent proteinuria. Participants with OP also provided a random urine sample 3 years after OP diagnosis. Investigators determined the frequency of OP among the study population and assessed whether there were any differences in demographics and anthropometric measurements between those with and without OP.

There were 1,701 children included in analysis, 51.8% of whom were boys. The mean age of participants was 10.5 years. Overall, 48 (2.8%) participants had transient proteinuria, 5 (0.29%) had persistent proteinuria, and 11 (0.65%) were diagnosed with OP. There were no statistically significant differences in age, gender, or BMI between those with and without OP. A follow-up urine sample was obtained from 7 of the 11 participants with OP 3 years after diagnosis; in all 7, the proteinuria had resolved.

The investigators conclude that the prevalence of OP is <1% and appears to resolve spontaneously in a few years.

Dr Sanchez-Kazi has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.

Orthostatic proteinuria is defined as absence of proteinuria during supine position and presence of proteinuria during upright ambulation with total urine protein <1,000 mg per day. It is thought to be a benign condition in children and resolve spontaneously without intervention. Diagnosis of OP requires a first-morning urine sample and an afternoon urine sample for calculation of protein-to-creatinine ratios. In one study, renal biopsies obtained in children with OP showed no specific histologic lesions, although some complement and immunoglobulin deposition have been described, which may suggest previous or present glomerulonephritis. Doppler renal ultrasound in some studies showed left renal vein entrapment between the abdominal aorta and the superior mesenteric artery, known as “nutcracker” syndrome.3,4  Long-term follow-up of these children with nutcracker syndrome also showed spontaneous resolution of proteinuria.3,4  Several theories have been proposed to explain OP, including possible exaggerated response...

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