What is Orthostatic Proteinuria (postural proteinuria)?
Orthostatic proteinuria, or postural proteinuria, is a condition that leads to a higher than normal amount of protein in a person’s urine when they are standing up. However, when they are lying down, the protein levels in their urine is normal. This condition affects about 2 to 5% of teenagers but it’s unusual to see it in individuals older than 30. It’s also a harmless condition. Therefore, it’s essential to accurately diagnose orthostatic proteinuria so that unnecessary medical procedures like a kidney biopsy are avoided.
The cause of orthostatic proteinuria is not completely understood – there are a few theories about why it happens. Some suggest that it might simply be a normal variant, others propose that it might be due to a minor issue with the glomeruli (tiny structures in your kidneys where urine is produced). Another theory is that it might be a reaction to how the body maintains blood flow, while some suggest that it could be due to the left renal vein (which carries blood away from the left kidney) being compressed.
People with a lower Body Mass Index (BMI) are more likely to have ongoing orthostatic proteinuria in comparison to those with a higher BMI, possibly due to the changing distance between two large arteries in the body (the superior mesenteric artery and the aorta) based on one’s BMI. We will discuss the causes, prevalence, how it develops, how it’s diagnosed, and how it’s managed in further detail.
What Causes Orthostatic Proteinuria (postural proteinuria)?
Orthostatic proteinuria is a condition where a person has high levels of protein in their urine after standing up. Several theories try to explain why this occurs:
– It might be a normal variant. A study backed this idea, where 120 healthy men, aged 11 to 36, had their urine tested after lying down and after standing up. They found out that 20% of them had higher protein levels in their urine after standing up for just an hour. The remaining 80% actually saw a decrease in protein levels when they stood up, which makes the researchers think that everyone’s bodies respond differently when standing.
– There could be some slight defect impacting the kidneys’ filters, known as the glomeruli. A study compared the kidneys of 55 healthy young men in Singapore. Some of them had constant high protein levels in their urine, and others only had high levels when standing up. They found that men with standing protein levels had small defects in their glomeruli, which could be causing the protein leakage. Going along the same lines, another study of 56 healthy young men found the wall of the kidney’s filters thickened in 43% of them, which might be why they had high protein levels in their urine when standing.
– It could be due to a heightened response of how the body controls blood pressure when changing positions. An article critiqued this theory and proposed the idea that high protein levels in urine when standing are likely due to a combination of different reasons, with this being merely one of them. The renin-angiotensin-aldosterone system, which aids in kidney function, could also play a role in this process.
– Lastly, this condition might be due to the left renal vein getting squished. There is a theory that when we stand, the left renal vein gets partially blocked. This blockage causes changes in the microscopic circulation within the kidney, increasing the filtration of protein when a person stands, thereby causing orthostatic proteinuria.
Risk Factors and Frequency for Orthostatic Proteinuria (postural proteinuria)
Orthostatic proteinuria, a condition where protein is found in the urine, is the leading reason for isolated proteinuria (excessive protein in urine) in adolescents and children. It impacts around 2 to 5% of all teenagers but is rare after the age of 30. Generally, boys are more often affected by this condition. However, it’s unclear whether overweight or underweight children are at a higher risk of developing orthostatic proteinuria as different studies have shown contrasting results.
Signs and Symptoms of Orthostatic Proteinuria (postural proteinuria)
When a patient is suspected of having a kidney condition or orthostatic proteinuria, it’s important to gather a comprehensive medical history and conduct a full physical examination. If the patient is a child, their guardian should assist in providing this information. Notably, if the patient or their family has a history of kidney disease, this could hint at a different medical issue, rather than orthostatic proteinuria being the problem.
Testing for Orthostatic Proteinuria (postural proteinuria)
If your doctor suspects that you may have a condition called orthostatic proteinuria, a condition where the body excretes an unusual amount of protein through urine while standing, they most likely will ask you to provide a urine sample first thing in the morning. This sample helps determine the amount of protein in your urine. If the protein in your first-morning urine sample is within a normal range – that is usually less than 150 mg/day – it’s unlikely that further tests for kidney disease are needed.
There’s generally no need for a renal biopsy or kidney tissue sample with orthostatic proteinuria, unless there are other troubling signs. These signs can include symptoms of blood vessel inflammation, unusual substances in your urine, high blood pressure, visible or persistent blood in your urine, kidney dysfunction, or low levels of a protein called complement.
The presence of protein and blood in your urine simultaneously may indicate a more serious issue with your kidneys. In such case, your doctor will carry out further tests to understand the cause.
To confirm the diagnosis, your doctor may also check the ratio of protein to a substance called creatinine in your urine. You’ll likely be tested while lying down and while standing up. If your protein-to-creatinine ratio is lower when you’re lying down (less than 0.2mg/mg creatinine) and increases when you’re standing, it can confirm the diagnosis of orthostatic proteinuria.
Treatment Options for Orthostatic Proteinuria (postural proteinuria)
Orthostatic proteinuria is a condition where your body excretes too much protein in your urine. Although there are no official guidelines for monitoring this condition, the general recommendation is to see your doctor once a year for a check-up. Even with this condition, you don’t need to change your diet or limit how much you exercise.
If you have this condition but aren’t experiencing any symptoms (asymptomatic orthostatic proteinuria), you won’t need surgery. Stenting, which involves using a small tube to open up a blocked or narrow blood vessel, isn’t recommended. Some doctors might suggest medications such as angiotensin-converting enzyme (ACE) inhibitors to treat this condition, but these aren’t typically used for asymptomatic isolated orthostatic proteinuria.
What else can Orthostatic Proteinuria (postural proteinuria) be?
Continued presence of protein in the urine, known as persistent proteinuria, is something that doctors should always consider among their diagnoses. There are multiple reasons why a child may have protein in their urine:
- Transient proteinuria, which is temporary
- Alport syndrome, a genetic condition affecting the kidneys
- Diabetes mellitus, a condition where the body can’t regulate blood sugar properly
- Glomerulopathy, diseases that injure the kidneys’ tiny filters
- Infections
- Cancer (malignancies)
- Toxins
- Acute tubular necrosis, a kidney disorder involving damage to the tubule cells of the kidneys
- Polycystic kidney disease, a genetic disorder causing many cysts to grow in the kidneys
- Proximal renal tubular acidosis, a condition that causes acid to build up in the blood.
What to expect with Orthostatic Proteinuria (postural proteinuria)
Orthostatic proteinuria is a harmless condition. This was found in a long-term study spanning 20 years by Springberg et al., which showed no proof of worsening kidney disease in patients with orthostatic proteinuria. In simpler terms, orthostatic proteinuria does not likely lead to serious kidney complications.
In a follow-up evaluation by the same team, they re-examined 64 patients that another group of researchers, Robinson et al., had studied 20 years earlier. They were able to get detailed information from 36 out of the 64 original patients, and only six patients were found to have qualitative proteinuria – meaning their urine had above-normal protein levels. Importantly, none out of these 64 patients had to undergo treatment in the form of kidney transplantation or dialysis, which is a medical procedure to filter and clean the blood when the kidneys can’t, in the Veterans Administration hospital system.
Possible Complications When Diagnosed with Orthostatic Proteinuria (postural proteinuria)
Orthostatic proteinuria is often considered a harmless condition, with no known complications. This means it doesn’t cause any negative health effects.
Preventing Orthostatic Proteinuria (postural proteinuria)
Educating patients is a key part of dealing with orthostatic proteinuria, a condition where there is an unusual amount of protein in the urine. Even though having protein in the urine is not normal, it’s important for patients to understand what this disease means for their health.
