Proteinuria describes a condition in which urine contains an abnormal amount of protein. Proteins are the building blocks for all body parts, including muscles, bones, hair, and nails. Proteins in your blood also perform a number of important functions: protecting you from infection, helping your blood coagulate, and keeping the right amount of fluid circulating through your body.
As blood passes through healthy kidneys, they filter the waste products out and leave in the things the body needs, like proteins. Most proteins are too big to pass through the kidneys’ filters into the urine, unless the kidneys are damaged. The two proteins that are most likely to appear in urine are albumin and globulin. Albumin is smaller and therefore more likely to escape through the filters of the kidney, called glomeruli. Albumin’s function in the body includes retention of fluid in the blood. It acts like a sponge, soaking up fluid from body tissues.
Inflammation in the glomeruli is called glomerulonephritis, or simply nephritis. Many diseases can cause this inflammation, which leads to proteinuria. Additional processes that can damage the glomeruli and cause proteinuria include diabetes, hypertension, and other forms of kidney diseases.
Research shows that the level and type of proteinuria (whether the urinary proteins are only albumin or include other proteins) strongly determine the extent of damage and whether you are at risk for developing progressive kidney failure.
Proteinuria has also been shown to be associated with cardiovascular disease. Damaged blood vessels may lead to heart failure or stroke as well as kidney failure. If your doctor finds that you have proteinuria, you will want to do what you can to protect your health and prevent any of these diseases from developing.
Several health organizations recommend that some people be regularly checked for proteinuria so that kidney disease can be detected and treated before it progresses. A 1996 study sponsored by the National Institutes of Health determined that proteinuria is the best predictor of progressive kidney failure in people with type 2 diabetes. The American Diabetes Association recommends regular urine testing for proteinuria for people with type 1 or type 2 diabetes. The National Kidney Foundation recommends that routine checkups include testing for excess protein in the urine, especially for people in high-risk groups.
Who Is at Risk?
People with diabetes, hypertension, or certain family backgrounds are at risk for proteinuria. In the United States, diabetes is the leading cause of end-stage renal disease (ESRD), the result of progressive kidney failure. In both type 1 and type 2 diabetes, the first sign of deteriorating kidney function is the presence of small amounts of the protein albumin in the urine, called microalbuminuria. As kidney function declines, the amount of albumin in the urine increases, and microalbuminuria becomes full-fledged proteinuria.
High blood pressure is the second leading cause of ESRD. Proteinuria in people with high blood pressure is an indicator of declining kidney function. If the hypertension is not controlled, the person can progress to full renal failure.
African Americans are more likely than white Americans to have high blood pressure and to develop kidney problems from it, even when their blood pressure is only mildly elevated. In fact, African Americans ages 25 to 44 are 20 times more likely than their white counterparts to develop hypertension-related kidney failure. High blood pressure is the leading cause of kidney failure among African Americans.
Other groups at risk for proteinuria are American Indians, Hispanic Americans, Pacific Islander Americans, older people, and overweight people. People who have a family history of kidney disease should also have their urine tested regularly.
What Are the Signs of Proteinuria and Kidney Failure?
Large amounts of protein in your urine may cause it to look foamy in the toilet. Also, because the protein has left your body, your blood can no longer soak up enough fluid and you may notice swelling in your hands, feet, abdomen, or face. Alternatively, you may have proteinuria without noticing any signs or symptoms. Testing is the only way to find out how much protein you have in your urine.
What Are the Tests for Proteinuria?
To test for proteinuria, you will need to give a urine sample. A strip of chemically treated paper will change color when dipped in urine that has too much protein. A more sophisticated chemical analysis is needed to find smaller amounts (microalbuminuria). The most dependable measure of proteinuria requires you to collect your urine for 24 hours. You will be given a special container and instructions for starting and stopping the collection and for storing the container.
Your doctor will also want to test a sample of your blood for creatinine and urea nitrogen. These are waste products that healthy kidneys remove from the blood. High levels of creatinine and urea nitrogen in your blood indicate that kidney function is impaired.
How Is Proteinuria Treated?
If you have diabetes, hypertension, or both, the first goal of treatment will be to control your blood sugar and blood pressure. If you have diabetes, you should test your blood sugar often, follow a healthy eating plan, take your medicines, and get plenty of exercise. If you have diabetes and high blood pressure, your doctor may prescribe a medicine from a class of drugs called ACE (angiotensin-converting enzyme) inhibitors. These drugs have been found to protect kidney function even more than other drugs that provide the same level of blood pressure control.
People who have high blood pressure and proteinuria but not diabetes may also benefit from taking an ACE inhibitor. The National Heart, Lung, and Blood Institute recommends keeping blood pressure below 125/75 mm Hg for people with proteinuria greater than 1 gram per 24 hours.
In addition to blood sugar and blood pressure control, the National Kidney Foundation recommends restricting dietary salt and protein. Your doctor may refer you to a dietitian to help you follow a healthy eating plan.
Hope Through Research
In recent years, researchers have learned much about kidney disease. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) sponsors several programs aimed at understanding kidney failure and finding treatments to stop its progression.
NIDDK’s Division of Kidney, Urologic, and Hematologic Diseases (DKUHD) supports basic research into normal kidney function and the diseases that impair normal function at the cellular and molecular levels, including diabetes, high blood pressure, glomerulonephritis, and other diseases marked by proteinuria.
Points To Remember Proteinuria is a condition in which urine contains an abnormal amount of protein. Proteinuria may be a sign that your kidneys are damaged and that you are at risk for end-stage renal disease. Several health organizations recommend that people be regularly checked for proteinuria so that kidney disease can be detected and treated before it progresses. Groups at risk for proteinuria and kidney failure include African Americans, American Indians, Hispanic Americans, Pacific Islander Americans, people who are older or overweight, and people who have a family history of kidney disease. You may have proteinuria without noticing any signs or symptoms. Testing is the only way to find out how much protein you have in your urine. If you have diabetes or hypertension, or both, the first goal of treatment will be to control your blood sugar or blood pressure.
For More Information
American Kidney Fund
6110 Executive Boulevard
Rockville, MD 20852
Phone: (800) 638-8299 or (301) 881-3052
National Kidney Foundation
30 East 33rd Street
New York, NY 10016
Phone: (800) 622-9010 or (212) 889-2210
National Kidney and Urologic Diseases Information Clearinghouse
3 Information Way
Bethesda, MD 20892-3580
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NIH Publication No. 01-4732