Proteinuria



Last Review Date: June 7, 2017


What is it?

Proteinuria is a condition characterised by the presence of greater than normal amounts of protein in the urine. It is associated with a variety of different diseases and is sometimes seen in those who are apparently healthy. Mild or transient proteinuria may become more severe over time.

Plasma, the liquid portion of blood, contains many different proteins. One of the many functions of the kidneys is to conserve plasma protein so that it is not excreted along with waste products when urine is produced. There are two mechanisms that normally prevent protein from passing into urine: (1) the glomeruli provide a filter that keeps most larger plasma proteins inside the blood vessels and (2) the small proteins that do get through are almost entirely reabsorbed by the tubules. For additional details on kidneys and how they function, see the page on How Kidneys Work on the DaVita website.

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.

A variety of diseases and conditions are associated with proteinuria. Two of the most common causes are:

Others causes include:

Pregnant women are frequently screened for proteinuria because its development is associated with preeclampsia (also known as toxaemia), a hypertensive disorder that can cause oedema, nausea and headaches during pregnancy. Preeclampsia can be dangerous for both the mother and her baby.

Proteinuria due to the presence of excess small proteins in blood may be seen in multiple myeloma (free immunoglobulin light chains) and in conditions that cause the breakage of red blood cells (release of haemoglobin).

Healthy people can have transient or persistent proteinuria. It is associated with stress, exercise, fever, aspirin therapy, and exposure to cold. Some people excrete more protein into the urine when they are standing up than when they are lying down (orthostatic proteinuria).

Signs and symptoms

There are frequently no symptoms associated with proteinuria, especially in mild cases. Large amounts of protein may cause the urine to appear foamy. Significant loss of protein from the blood can affect the body’s ability to regulate fluids, which can lead to swelling in the hands, feet, abdomen and face. When symptoms are present, they are usually associated with the condition or disease causing proteinuria.


Tests

The goals of testing for proteinuria include screening those at risk, detecting the condition, determining its underlying cause, evaluating the type and quantity of protein being released, and evaluating kidney function. When proteinuria is detected, patients are monitored at intervals to see if it resolves or becomes worse. Both urine and blood tests may be ordered to evaluate proteinuria.

Laboratory tests

Several tests may be ordered on either 24-hour or random urine samples:

  • Urinalysis – evaluation of a urine sample by visual inspection, chemical testing and, in some cases, microscopic analysis.
  • Protein urine, 24-hour urine – measures the amount of protein excreted in the urine in a 24-hour period; this is a more accurate assessment of the degree of proteinuria than a random urine.
  • Albumin/creatinine ratio (UACR), random urine - measures albumin in a random sample and corrects it for the amount of creatinine (a substance released by the body at a steady rate); alternative to 24-hour sample.
  • Protein/creatinine ratio (UPCR), random urine - measures protein in a random sample and corrects it for the amount of creatinine; alternative to 24-hour sample.

A few tests may be run on both urine and blood:

  • Creatinine urine - uses a 24-hour urine sample and a blood sample to evaluate kidney function based on the rate of creatinine excretion from the body.
  • Protein electrophoresis - a test used to determine the different types and relative concentrations of protein present in the urine; may also be performed to evaluate protein in the blood.

These tests may also be ordered and are run primarily on blood only:

  • eGFR (estimated glomerular filtration rate) - uses a blood creatinine level to calculate the estimated rate of urine filtration; rate decreases with progressive kidney damage.
  • Urea - a blood test used to evaluate kidney function.
  • Creatinine - a blood test used to evaluate kidney function; less frequently, it may be done on urine. (Note: Although creatinine may be measured in urine samples, it is usually measured to be included as part of a ratio or calculation.)
  • Total protein - a blood test that measures all of the protein in the serum.
  • Albumin - a blood test that measures the concentration of albumin in blood.

A kidney biopsy may also be ordered. This is a procedure that is sometimes performed to look at a small sample of kidney tissue under the microscope for evidence of kidney disease or damage.

Non-laboratory tests

  • Imaging scans of the kidney to detect the presence and determine the severity of kidney disease or damage.
  • Blood pressure; may be measured as part of investigation of cause of proteinuria; frequently monitored in those who have hypertension or are at risk of developing it.

Treatment

The goals of treatment are to control the underlying conditions causing proteinuria and to minimise its progression. Treatment for each condition is likely to be different. For example, controlling blood sugar levels in patients with diabetes will help to preserve kidney function. In patients with hypertension, it is important to control blood pressure to prevent progressive kidney damage. Preeclampsia-related proteinuria usually resolves once the baby is born.

In some patients with persistent proteinuria, the doctor may recommend dietary changes such as altering the amount of protein consumed. No treatment may be necessary for mild or transient proteinuria.


Related pages

On this site
Tests: Protein urine, urinalysis, albumin, microalbumin, protein electrophoresis, total protein, eGFR, urea, creatinine, creatinine urine
Conditions: Kidney disease, diabetes, hypertension, pregnancy

Elsewhere on the web
Kidney Health Australia: Proteinuria
National Institute of Diabetes and Digestive and Kidney Diseases (US): Proteinuria, Your Kidneys and How They Work
National Kidney Foundation (US): What You Should Know About Proteinuria
American Diabetes Association: Kidney Disease (nephropathy)
March of Dimes: High Blood Pressure During Pregnancy