What is orthostatic proteinuria?
Orthostatic or postural proteinuria, by definition, is demonstration of increased urine protein excretion in the upright position and normal urine protein excretion in the supine position.
It is a benign condition, typically seen in adolescents, whose mechanism is not clearly understood. The diagnosis is established by performing a split urine collection.
The protocol for a split urine collection is as follows:
(1) The first morning void is discarded.
(2) A 16-hour upright collection is obtained between 7 am and 11 pm , with the patient performing normal activities and finishing the collection by voiding just before 11 pm . (The times can be adjusted according to the normal sleep/wake times.)
(3) The patient should assume the recumbent position 2 hours before the upright collection is finished to avoid contamination of the supine collection with urine formed when in the upright position.
(4) A separate overnight 8-hour collection is obtained between 11 pm and 7 am .
Orthostatic proteinuria is diagnosed if the urinary protein excretion rate is normal for the nighttime collection (for children <4 mg/m 2 per hour and for adults <50 mg over an 8-hour period) and the daytime collection exceeds the normal protein excretion rate.
Orthostatic proteinuria has a benign course and does not progress to end-stage kidney disease; in fact, proteinuria resolves spontaneously in the majority of affected patients.
