Chapter 519 Orthostatic (Postural) Proteinuria

Orthostatic proteinuria is the most common cause of persistent proteinuria in school-aged children and adolescents, occurring in up to 60% of children with persistent proteinuria. Children with this condition are usually asymptomatic, and the condition is discovered on routine urinalysis. Patients with orthostatic proteinuria excrete normal or minimally increased amounts of protein in the supine position. In the upright position, urinary protein excretion may be increased 10-fold, up to 1,000 mg/24 hr (1 g/24 hr). Hematuria, hypertension, hypoalbuminemia, edema, and renal dysfunction are absent.

In a child with persistent asymptomatic proteinuria the initial evaluation should include an assessment for orthostatic proteinuria, a condition in which the 24-hr urinary protein excretion rarely exceeds 1 g. It begins with the collection of a first morning urine sample, with subsequent testing of any urinary abnormalities by a complete urinalysis and determination of a spot protein : creatinine (Pr : Cr) ratio. The correct collection of the first morning urine sample is critical. The child must fully empty the bladder before going to bed and then collect the first voided urine sample immediately upon arising in the morning. The absence of proteinuria (dipstick negative or trace for protein and urine Pr : Cr ratio <0.2) in the first morning urine sample for 3 consecutive days confirms the diagnosis of orthostatic proteinuria. No further evaluation is necessary, and the patient and family should be reassured of the benign nature of this condition. However, if there are other abnormalities of the urinalysis (e.g., hematuria) or the urine Pr : Cr ratio is >0.2, the patient should be referred to a pediatric nephrologist for a complete evaluation.

The cause of orthostatic proteinuria is unknown, although altered renal hemodynamics and partial renal vein obstruction in the upright position are possible causes. Long-term follow-up studies in young adults suggest that orthostatic proteinuria is a benign process, but similar data are not available for children. Therefore, long-term follow-up of children may be prudent to monitor patients for evidence of kidney disease, including hematuria, hypertension, edema, diminished renal function, or proteinuria exceeding 1,000 mg/24 hr.