The kidneys' job is to remove wastes and excess water and salts from the blood. Kidneys receive blood through the renal arteries (figure 1). The blood flows into parts of the kidney called nephrons (figure 2). Each nephron is made of a glomerulus and a tubule. Each kidney contains hundreds of thousands of nephrons.
The glomeruli filter the blood, removing waste products from the blood. They also prevent some substances, such as protein, from being taken out of the blood. If the glomeruli are damaged, protein from the blood leaks into the urine.
Normally, you should have less than 150 milligrams (about 3 percent of a teaspoon) of protein in the urine per day. Having more than 150 milligrams per day is called proteinuria.
DOES PROTEINURIA CAUSE SYMPTOMS?
People with a small amount of proteinuria generally have no signs or symptoms. However, some patients have edema (swelling) in the face, legs, or both if they lose large amounts of protein in their urine.
TYPES OF PROTEINURIA
Proteinuria can be divided into three categories: transient (intermittent), orthostatic (related to sitting/standing or lying down), and persistent (always present).
Transient proteinuria — Transient (intermittent) proteinuria is by far the most common form of proteinuria. Transient proteinuria usually resolves without treatment. Stresses such as fever and exercise may cause transient proteinuria.
Orthostatic proteinuria — Orthostatic proteinuria occurs when one loses protein in the urine while in an upright position but not when lying down. It occurs in 2 to 5 percent of adolescents but is unusual in people over the age of 30 years. The cause of orthostatic proteinuria is not known. Orthostatic proteinuria is not harmful, does not require treatment, and typically disappears with age.
Orthostatic proteinuria is diagnosed by obtaining a split urine collection. This requires collecting two urine samples: one while you are standing or sitting up (usually during the day) and another after you have been sleeping for several hours (eg, first thing in the morning) (see 'Urine testing' below).
Persistent proteinuria — In contrast to transient and orthostatic proteinuria, persistent proteinuria occurs in people with underlying kidney disease or other medical problems. Examples include:
●Diseases that affect the kidney, such as diabetes mellitus
●Diseases that cause the body to overproduce certain types of protein
Urine testing — Proteinuria is diagnosed by analyzing the urine (called a urinalysis), often with a dipstick test. However, dipstick testing is not very precise. Also, people should have the urine test repeated to determine whether or not the proteinuria is transient or persistent.
The urine should also be examined with a microscope to see whether there are cells, crystals, bacteria, or structures called casts. These urine elements can be signs of specific types of kidney problems (for example, diseases that injury the glomeruli). (See "Patient information: Glomerular disease overview (Beyond the Basics)".)
If two or more urinalyses show protein in the urine, the next step is to determine how much protein is in the urine. This can be measured from:
●A single urine sample collected at any time (a common and convenient method).
●Urine that has been collected over 24 hours (a more exact but somewhat inconvenient method). (See "Patient information: Collection of a 24-hour urine specimen (Beyond the Basics)".)
If your doctor or nurse asks you to collect urine at home, try to keep it in a cool place, like the refrigerator.
Blood testing — Your doctor or nurse might also ask you to have blood tests to see how well your kidneys are working (called kidney function testing). These include measurement of BUN (blood urea nitrogen) and creatinine and then calculating how well the kidneys work with a formula to determine the glomerular filtration rate.
Kidney biopsy — Your doctor might recommend a test called a kidney biopsy. During a biopsy, a doctor takes a small piece of one kidney and then looks at the tissue under the microscope. Many people with proteinuria will not need a kidney biopsy. (See "Patient information: Renal (kidney) biopsy (Beyond the Basics)".)
PROTEINURIA TREATMENT AND PROGNOSIS
Transient and orthostatic proteinuria are not harmful conditions, and no specific treatment is needed.
Patients with persistent low-grade proteinuria that is not related to decreased kidney function or a systemic disease typically have no long-term complications, even if untreated. Many nephrologists use an antihypertensive drug, such as an angiotensin-converting enzyme (ACE) inhibitor, to reduce or eliminate proteinuria.
In patients with persistent high-grade proteinuria who have decreased kidney function, the underlying condition is usually treated. (See "Patient information: Chronic kidney disease (Beyond the Basics)".)
●Normally, protein should not be found in the urine. A person who has protein in the urine is said to have proteinuria.
●Most people have no signs or symptoms of proteinuria.
●Proteinuria is usually discovered with a urine dipstick test that is done for another reason.
●There are three types of proteinuria: transient (temporary), orthostatic (related to sitting/standing or lying down), and persistent (always present).
●Certain types of urine testing are needed to determine the type of proteinuria. Depending upon these results, other tests may be needed, including blood tests and, sometimes, a kidney biopsy.
●Proteinuria should always be evaluated by a clinician.
●Transient and orthostatic proteinuria do not cause long-lasting health problems and do not usually need to be treated.
●Some people with persistent proteinuria have kidney problems that need to be treated.
WHERE TO GET MORE INFORMATION
Your healthcare provider is the best source of information for questions and concerns related to your medical problem.
This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.
Patient level information — UpToDate offers two types of patient education materials.
The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.
Patient information: Chronic kidney disease (The Basics)
Patient information: Medicines for chronic kidney disease (The Basics)
Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.
Patient information: Glomerular disease overview (Beyond the Basics)
Patient information: Collection of a 24-hour urine specimen (Beyond the Basics)
Patient information: Renal (kidney) biopsy (Beyond the Basics)
Patient information: Chronic kidney disease (Beyond the Basics)
Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.
Assessment of urinary protein excretion and evaluation of isolated non-nephrotic proteinuria in adults
Proteinuria in pregnancy: Evaluation and management
Orthostatic (postural) proteinuria
Overview of heavy proteinuria and the nephrotic syndrome
The following organizations also provide reliable health information.
●National Library of Medicine
●National Institute of Diabetes and Digestive and Kidney Diseases
●National Kidney Foundation
●American Kidney Fund
●American Association of Kidney Patients