Orthostatic proteinuria occurs in between 2-5% of all adolescents–it is primarily a pediatric condition, rarely occurring after age 30. Orthostatic proteinuria refers to the condition of an individual having proteinuria only while upright; the urine protein level returns to normal while lying down. I use the term “condition” rather than “disease” because orthostatic proteinuria carries with it a benign prognosis with no danger of worsening renal function.
What is the pathogenesis of orthostatic proteinuria? There are several theories, though the precise etiology is not known. One possibility is that individuals with an exaggerated hemodynamic response to being in the upright position–manifested by increased secretion of angiotensin II and norepinephrine–might lead to transiently increased glomerular permeability to protein. Another theory is that some degree of “nutcracker syndrome”–in which the left renal vein is squeezed or kinked between the aorta and superior mesenteric artery–is at play more commonly in the upright position than while lying down.