Orthostatic proteinuria

OVERVIEW

What is orthostatic proteinuria?

Normally, very little protein is excreted in urine. If protein excretion increases in an upright position but remains normal when lying on the back or side, it is called orthostatic proteinuria or postural proteinuria.

Orthostatic proteinuria is the most common cause of isolated proteinuria in children (especially adolescents).

What is the normal urine protein excretion for children and adults?

Normal urinary protein excretion in children is less than 100 mg/(m²·d) [ < 4 mg/(m²·h)] or a total of less than 150 mg/d.
Normal urinary protein excretion in adults is less than 50 mg per 8 hours or a total of less than 150 mg/d.

Who is most likely to have orthostatic proteinuria?

This condition is commonly seen in children and adolescents.

Is orthostatic proteinuria common?

Orthostatic proteinuria accounts for 60% of all cases of persistent daytime proteinuria in children and 75% of adolescent proteinuria cases. It is less common in adults over 30 years old.

SYMPTOMS

What are the common manifestations of orthostatic proteinuria?

This condition is generally asymptomatic and is usually discovered incidentally during urinalysis for unrelated illnesses or routine physical examinations.

Can orthostatic proteinuria cause serious consequences?

This condition does not lead to serious consequences nor affect kidney function. Over time, it tends to resolve.

CAUSES

What are the causes of orthostatic proteinuria?

Currently, the possible causes of this condition include:

Normally, changing from a supine to an upright position increases urinary protein excretion, and in some individuals, this normal response may be exaggerated; these are normal phenomena.
Blood entering the glomerulus for filtration is one of the key steps in urine formation. Minor glomerular abnormalities or the release of vasoconstrictive hormones after standing, which "enhances" the glomerulus's filtration capacity, can increase protein excretion.
Compression of the left renal vein increases glomerular filtration of protein.

DIAGNOSIS

How should orthostatic proteinuria be diagnosed?

The diagnosis of orthostatic proteinuria can be made when urinary protein excretion is normal in the supine position but increases in the upright position.

What tests are needed for orthostatic proteinuria?

Urinalysis, comparison of supine and upright urinary protein/creatinine ratios, 24-hour urine protein quantification (daytime and nighttime), and renal and renal vascular ultrasound.

Why are these tests necessary for orthostatic proteinuria? What is their purpose?

Urinalysis: Used to screen for proteinuria, though it may underestimate protein levels.
Supine and upright urinary protein/creatinine ratios: The simplest method for diagnosing orthostatic proteinuria.
Daytime and nighttime urine protein quantification: Used when supine and upright urinary protein/creatinine ratios are inconclusive.
Renal and renal vascular ultrasound: Assesses kidney morphology and blood flow to help identify the cause of proteinuria.
Additional tests such as CT, MRI, or renal venography may be required if necessary.

What precautions should be taken for urine tests related to orthostatic proteinuria?

Sampling method for supine and upright urine samples: Empty the bladder completely before going to bed. Collect the first morning urine immediately upon waking as the supine sample. Then, collect urine after standing and moving normally for at least 1 hour as the upright sample.
Daytime urine collection method: After discarding the first morning urine, collect all urine passed during the day while maintaining normal activities. Collect the last urine sample before bedtime to complete daytime collection.
Nighttime urine sampling method: Collect all urine passed during sleep, including the first morning urine upon waking, to complete nighttime collection.
Intense exercise (15–20 minutes) can also increase proteinuria. Therefore, wait at least 24 hours after vigorous exercise before collecting urine for testing.

Which conditions can orthostatic proteinuria be easily confused with?

This condition may be confused with transient proteinuria caused by fever or intense exercise, as well as persistent proteinuria due to chronic kidney disease. Differentiation can be made based on medical history and the aforementioned tests.

TREATMENT

Which department should I visit for orthostatic proteinuria?

Nephrology.

How is orthostatic proteinuria treated?

As mentioned earlier, this condition does not cause serious consequences or affect kidney function, and tends to improve over time.

Therefore, in most cases, treatment is not recommended. For patients with this condition caused by left renal vein compression, a minority may consider surgical treatment, but indications must be strictly followed.

Does orthostatic proteinuria require follow-up?

Regular follow-up urine tests can be scheduled based on the doctor's recommendation.

Can orthostatic proteinuria resolve on its own?

In some patients, proteinuria is not persistent and may decrease or even resolve spontaneously.