Protein in Urine (Proteinuria)

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  • Also Known As:
  • Albuminuria
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What is proteinuria?

Proteinuria is a condition that occurs when there is a greater than normal amount of protein in the urine. It is usually associated with some kind of underlying disease or abnormality but may occasionally be seen in healthy individuals.

Urine normally contains a small amount of protein. The kidneys, which are part of the urinary tract, filter wastes from the blood and produce urine. The liquid portion of blood (plasma) contains many different proteins and one of the many functions of the kidneys is to prevent plasma protein from being eliminated along with waste products when urine is produced. There are two mechanisms that normally prevent protein from passing into urine:

  1. Within the kidneys are about a million tiny blood filtering units called nephrons. In each nephron, blood is continually filtered through a cluster of looping blood vessels, called a glomerulus (plural is glomeruli). The glomeruli provide a barrier that keeps most larger plasma proteins inside the blood vessels.
  2. Attached to each glomerulus are tubes (tubules) that have a number of sections that collect the fluid and molecules that pass through the glomerulus. The small proteins that do get through the glomerulus are almost entirely reabsorbed by the tubules.

Proteinuria most often occurs when either the glomeruli or tubules in the kidney are damaged. Inflammation and/or scarring of the glomeruli can allow increasing amounts of protein and sometimes red blood cells (RBCs) to leak into the urine. Damage to the tubules can prevent protein from being reabsorbed. Proteinuria may also develop when too much of a small protein is present in the blood and the tubules cannot reabsorb all of it.

There are conditions that can cause healthy people to have temporary (or transient) or persistent proteinuria but don’t necessarily indicate kidney damage. Examples include dehydration, stress, strenuous exercise, fever, aspirin therapy, and/or exposure to extreme cold.

Some people release more protein into their urine when they are standing up than when they are lying down (orthostatic proteinuria), though this condition is rare in individuals over age 30.

However, too much protein in the urine usually indicates the presence of an underlying disease or condition and warrants further investigation to determine the cause.

The most common cause of protein in the urine is kidney damage resulting from:

  • Diabetes – proteinuria is one of the first signs of deteriorating kidney function in people with type 1 and 2 diabetes.
  • Hypertension – proteinuria in people with high blood pressure is also a first sign of declining kidney function.

Some examples of other causes of kidney damage resulting in proteinuria include:

Some additional conditions that can cause proteinuria include:

  • Red blood cell destruction and release of hemoglobin that occurs in the bloodstream (intravascular hemolysis)—this can occur with hemolytic anemia, for example.
  • Preeclampsia – pregnant women are routinely screened for proteinuria because its presence is associated with pre-eclampsia (also known as toxemia of pregnancy). Pre-eclampsia is a pregnancy-specific disorder where proteinuria and hypertension develop at the same time. Symptoms can include edema (swelling), nausea, and headaches during pregnancy. Rarely, it can cause severe symptoms such as seizures. Pre-eclampsia can be dangerous for both the mother and her baby.
  • Multiple myeloma (cancer of the plasma cells) – proteinuria due to the presence of excess proteins in blood that overflow into the urine (Bence-Jones protein) may be seen in multiple myeloma. Bence-Jones protein consists of an abnormal immunoglobulin light chain (either kappa or lambda) that is produced by monoclonal plasma cells.

 

About Proteinuria

Signs and Symptoms

There are frequently no symptoms associated with proteinuria, especially in mild cases. Laboratory testing is the only way to know for sure if you have protein in your urine. Several health organizations recommend regular urine tests for people at risk for chronic kidney disease and the associated proteinuria.

With increasing amounts of protein in the urine, there may be signs and symptoms:

  • Large amounts of protein may cause urine to appear foamy or frothy.
  • Significant protein loss from the blood can affect the body’s ability to regulate fluids, which can lead to swelling in the hands, feet, abdomen, and/or face (edema).

There may also be symptoms associated with the condition or disease causing the proteinuria.

Tests

The goals of testing for proteinuria include screening individuals who may be at risk, detecting the condition, determining its underlying cause, evaluating the type and quantity of protein being released, and evaluating kidney function. If proteinuria is detected, you will be monitored regularly over time to see if it resolves or becomes worse. Both urine and blood tests will be ordered to evaluate proteinuria.

Laboratory Tests

Screening for protein in the urine may be performed as part of a general health exam or as part of a check-up if you have a condition that may cause proteinuria. Some screening tests include:

  • Urine protein – detects the presence of any type of protein that may be in the urine. It can be performed alone on a random urine sample or as part of a urinalysis.
  • Urinalysis – an evaluation of a urine sample for several different substances that may be in the urine, including protein. This test may be used as part of a general health exam.
  • Urine albumin (microalbumin) – a sensitive test that is used to monitor people with diabetes for small amounts of albumin, the main blood protein, in the urine. Over time, diabetes can begin to affect kidney function and this test is an early indicator that diabetes has caused some kidney damage. The American Diabetes Association recommends that people diagnosed with type 2 diabetes be screened annually for low levels of albumin in the urine (microalbuminuria) and that people with type 1 diabetes be tested 5 years after diagnosis and annually thereafter.

A positive result on a screening test may be followed by further urine tests to determine how much protein and what type of protein is in the urine:

  • Urine albumin, 24 hour urine – measures the amount of albumin, which is one type of protein, released into the urine within that timeframe. This test may give the healthcare practitioner a better assessment as to the degree of kidney damage.
  • Urine albumin/creatinine ratio (ACR) – as an alternative to collecting urine for 24 hours, a random urine sample (not timed) may be used. In this test, creatinine is also measured. Creatinine is a waste product that is released into the urine at a steady rate. When both protein and creatinine are measured in a random sample, a urine albumin/creatinine ratio can be calculated. This calculation corrects for the amount of creatinine in the random sample, more accurately reflecting how much albumin has been lost in the urine.
  • Urine protein, 24-hour urine – measures the amount of all types of protein released into the urine within a 24-hour period; this is a more accurate assessment of the degree of proteinuria than a random urine test.
  • Urine protein/creatinine ratio (UPCR) – measures protein and creatinine in a random urine sample and corrects it for the amount of creatinine, similar to the ACR.
  • Urine protein electrophoresis (UPEP) – a test used to determine the different types and relative concentrations of protein present in the urine. The UPEP is often used for detecting the presence of Bence-Jones protein when multiple myeloma is suspected.
  • When the UPEP shows an abnormality, an immunofixation serum test may be performed to measure the abnormal protein, in addition to an immunoassay evaluation for free light chains.

In addition to testing urine, there are several other general laboratory tests that may be used to evaluate kidney function and/or help determine the cause of protein in the urine. Examples include:

  • Renal panel—a group of tests that may be used to evaluate kidney function and/or screen for, diagnose or monitor kidney disease. While the tests included in the panel can vary by laboratory, they typically include:
    • Electrolytes: sodium, potassium, chloride, bicarbonate (CO2) – help regulate the amount of fluid in the body and maintain the acid-base balance
    • Urea (urea nitrogen or blood urea nitrogen (BUN)) and Creatinine – blood tests used to evaluate kidney function; urea and creatinine are nitrogen-containing waste products that healthy kidneys move from the blood to the urine. If the kidneys are not functioning properly, urea and creatinine will remain in the blood and the levels will increase.
    • Phosphorus – a mineral that is vital for energy production, muscle and nerve function, and bone growth; it also plays an important role as a buffer, helping to maintain the body’s acid-base balance.
    • Calcium – one of the most important minerals in the body; it is essential for the proper functioning of muscles, nerves, and the heart and is required in blood clotting and in the formation of bones.
    • Albumin – a protein that makes up about 60% of protein in the blood and has many roles such as keeping fluid from leaking out of blood vessels and transporting hormones, vitamins, drugs, and ions like calcium throughout the body.
    • Glucose – supplies energy for the body; a steady amount must be available for use, and a relatively constant level of glucose must be maintained in the blood.
    • eGFR (estimated Glomerular Filtration Rate) – uses a blood creatinine level along with age and values assigned for sex and race to calculate the estimated rate of urine filtration; the eGFR rate decreases with progressive kidney damage.

The above tests may also be ordered individually.

  • Creatinine Clearance – measures creatinine in a 24-hour urine sample and a blood sample to calculate the amount of creatinine that has been cleared from the blood and passed into the urine; this calculation allows for a general evaluation of kidney function based on the rate of creatinine excretion from the body.
  • Total Protein (TP) – a blood test that measures all of the protein in the blood serum.

Other select tests may include:

In some cases, when kidney disease is suspected, a healthcare practitioner may also order a kidney biopsy. For this procedure, a small sample of the kidney tissue is collected and then examined by a pathologist using a microscope to look for evidence of kidney disease or damage. (For more, read the article on Anatomic Pathology.) A biopsy is sometimes used to help determine the nature and extent of structural damage to a kidney. Analyzing a small piece of kidney tissue, obtained using a biopsy needle and diagnostic imaging equipment, can sometimes be useful when disease of the glomeruli (or sometimes the tubules) is suspected.

Non-Laboratory Tests

  • Imaging scans of the kidney may be performed to detect the presence and determine the severity of kidney disease or damage. (For more on these, visit RadiologyInfo.org.)
  • Blood pressure may be measured as part of an investigation of the cause of proteinuria. It is frequently monitored in people who have hypertension or are at risk of developing it.

Treatment

Because different underlying conditions can cause proteinuria, treatment depends on the cause and usually focuses on resolving or managing the underlying condition and/or preventing it from getting worse.

For example, if you have diabetes or high blood pressure, carefully monitoring and controlling your condition helps to preserve kidney function and prevent progressive kidney damage.

In another example, proteinuria related to preeclampsia during pregnancy will be carefully monitored and usually resolves once the baby is born, though sometimes it can persist after delivery. Sometimes medications, such as blood pressure medication, will be prescribed depending on the severity of the pre-eclampsia.

For more details about treatment, see the resources in Related Content.

Related Content

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