What Is Proteinuria?

Overview

Protein is very important in the blood, within cells, and in organs, but protein found in your bodily waste (in urine) can be a significant issue. 

Proteinuria is when detectable amounts of protein are found within the urine. Protein is typically reabsorbed by the kidney and recycled for further uses by the body so when it is found to have leaked into the urine, doctors are concerned.

Protein is part of almost all cellular processes and is a waste product in many cellular processes. 

So if it’s a waste product, why is it a problem if it's excreted in urine?

The essential role that protein plays means that the body tries to utilise it maximally, using and reusing as much as possible in the process of ‘protein turnover’. It cannot be stored so is used in many ways; building new tissue, forming vital cellular components, or even as an energy source. The protein life cycle involves constant breakdown and rebuilding of protein – an average of 5.7g of protein per kg of body weight is broken down and 3g of protein per kg of body weight is rebuilt each day.¹ The difference between the two values is due to protein being used up as a fuel source, with dietary intake replacing this and allowing for the body’s key functions to continue.  

A leak in the well-oiled system of protein turnover is not something to be taken lightly.

The presence of proteinuria has been shown to lead to a significantly higher risk of death for those with other diseases – examples include heart disease, stroke, and cancer.^2,3,4 Some research has shown heart disease patients with proteinuria are almost three times more likely to suffer mortality than patients without.⁵ 

Whether it is solely a symptom of a bigger disease or a separate cause is unclear. What is clear, however, is that proteinuria can be a cause for serious concern.

Causes of proteinuria

Proteinuria is caused by insufficient function of the kidneys, specifically in a part of the kidney called the proximal tubule within the nephron.⁶ The function of the kidneys is to filter blood to allow waste to leave the body, and key nutrients to be retained. This is the final checkpoint where protein should be caught and retained in the blood rather than passing into urine alongside urea, salt, and other waste products. 

A significant and detectable amount of protein passing through the kidneys and into the urine is a sign of kidney damage. This can be caused by many different things.

Most directly, kidney disease (also known as renal disease) can produce the symptoms shown by proteinuria.⁷ Proteinuria is a strong indicator of kidney disease level, with more severe disease showing larger amounts of protein in the urine. This can be due to damage to the reabsorption structures in the kidney, but also due to the blood vessels in the kidney, where protein is commonly found.

Blood vessel damage is a major cause of proteinuria.

High blood pressure has been strongly linked to proteinuria, with researchers theorising that the damage caused to blood vessels allows protein to leak out of the bloodstream and into the kidney’s waste disposal section.⁸ Alongside the damage high blood pressure does to your heart, the stiffened inelastic blood vessels created by high blood pressure can cause significant irreversible kidney damage, easily detected by the large quantities of protein in urine.⁹ 

Likewise, improperly managed diabetes can lead to significant kidney damage and proteinuria.¹⁰ High blood sugar levels can create changes in the permeability (how large the vessel wall gaps are) of the blood vessels around the kidney as the vessels attempt to adapt to increased demands.¹¹ This process is slow and can take a number of years to develop but, mechanistically, is not dissimilar to the effects of high blood pressure in the stiffening and decreased function of blood vessels. 

Similarly, damage caused to the blood vessels by toxins released after smoking has also been shown to lead to kidney damage and proteinuria.¹² 

Additionally, there are also conditions that can cause damage to the filtering system of the kidney and lead to proteinuria.

Excess inflammation (overactive immune system) in the kidney can lead to damage to the reabsorption tubules. This is known as nephritis and tends to be more temporary with causes including certain medications (corticosteroids), excess exercise, and even exposure to cold temperatures.^13,14,15 This cause tends to be more reversible and goes away when removing the stimulus for inflammation. However, in cases of persistent excess inflammation, such as in autoimmune diseases, the damage to kidney filtering structures may be more significant and proteinuria may be a sign of more significant issues to investigate.¹⁶ 

Finally, dehydration has shown some links to proteinuria and may be a cause. A lack of water in the kidneys can cause excess build-up of waste molecules, which may cause damage to both blood vessels and the reabsorption structures, allowing protein molecules to pass into urine.¹⁷ 

Signs and symptoms of proteinuria

Proteinuria is not always obvious and most people with protein in their urine are asymptomatic.¹⁸

In more severe cases, symptoms may include:¹⁹

• Cloudy and foamy urine
• Pain when urinating
• Swollen joints

As proteinuria is often asymptomatic, you may only become aware you have this condition when investigating another issue.

Diagnosis

Fortunately, the diagnosis of protein in urine is fairly simple. It is a two-step process involving detection and then quantification – protein presence is confirmed then the amount and type of protein present is clarified.

The detection stage utilises a dipstick test. This is literally a small stick that is dipped into a urine sample that will change colour based on whether or not protein is present.²⁰ The sample is normally taken in the morning as this is when waste products are likely to be higher and a more detectable concentration of protein can be found. This test is most sensitive to the protein albumin which is a common protein found in proteinuria. This may also be a limitation as detectable quantities of other proteins are higher. Whilst this method detects the presence of protein and does allow some quantification of how much (by how strong a colour change is), further clarification of protein quantity present is required before any treatment plan is considered.

After the dipstick, the urinalysis continues and samples are taken throughout the day to determine the kind of proteinuria, and the quantity of each protein present. You will be asked to collect your urine every time you go to the toilet during the day. Scientists then run a series of tests on the urine to study the protein levels and how they may change throughout the day. From this information, they can find out whether the issue is a blood vessel issue or a filtering structure issue, and exactly which types of protein are present and their quantities.²⁰ 

Management and treatment for proteinuria

When proteinuria is mild, it may go unnoticed and the issue may disappear before you realise. 

Your doctor may recommend changing your current prescription or drinking more water, and urine protein levels may soon return to normal with no serious problems.

Persistent proteinuria, however, is much more problematic and can be a sign of a significant issue. This is something which will require further investigation and treatment to prevent severe negative outcomes. 

The treatment for persistent proteinuria is very much dependent on the type of larger issue present.

Diagnosed patients may receive blood pressure medication like ACE inhibitors or diabetes medication like exogenous insulin. They may be told to alter their diet to reduce salt or protein intake. They may be told to exercise more or even less intensely to promote healthier blood flow or reduce stress levels in their body. Sometimes more water is recommended via diet and sometimes less water is recommended when using diuretics.^21,22 

Treatment for proteinuria is not simple and is totally dependent on associated underlying conditions linked to this issue – proteinuria tends to clear up as the condition improves.

Regardless, it is important to not use a scattergun approach and do multiple things without your doctor's diagnosis and recommendation. Evidence has shown only risk when it comes to combining treatments unspecifically.²¹ When the correct and appropriate treatments are selected by your doctor to treat your specific condition, combination approaches can show significant improvements.²³

Get diagnosed and get the specific treatment plan for you.

FAQs

How can I prevent proteinuria?

Make healthy lifestyle choices by exercising regularly, avoiding smoking, and staying hydrated to reduce the risk of issues that can lead to proteinuria.

Who is at risk of proteinuria?

Those with diabetes, high blood pressure, and heart disease have shown an increased risk. Individuals assigned male at birth are also more at risk than individuals assigned female at birth, and those with higher body mass index (BMI) scores are also associated with increased risk.^18,24

How common is proteinuria?

Between 3% and 27% of the UK population are theorised to have proteinuria.²⁴

When should I see a doctor?

When consistently producing cloudy and foamy urine, particularly when alongside other issues.

Summary

Proteinuria can be a symptom of a serious condition, with the presence and severity of this issue associated with worse health outcomes in many diseases. Causes can vary but leakage of protein from blood vessels in the kidney and inefficient reabsorption are the issues that lead to protein in the urine. Diagnosis is a simple two-step process that your doctor can use to provide clarity on what the cause of proteinuria is specifically for you. Treatment plans can then be made to address the root cause, prevent significant poor health outcomes, and allow kidneys to function effectively again to limit protein being lost in the urine.