What is proteinuria?

Causes and Symptoms

Proteinuria is a disorder that does not have a unique cause. The excretion of abnormally high amounts of protein
in the urine can have a number of benign causes, in which case the disorder is likely transient. These causes include dehydration, acute illness, and overexertion. In other instances, proteinuria is the result of a problem within the kidneys. This type of proteinuria is more severe, as well as chronic. Proteins play an important function in the body and are routinely carried in the bloodstream. Since proteins are large molecules, they are not routinely filtered out by the kidneys into the urine. When the glomeruli (the filtering mechanisms within the kidneys) are damaged for any reason, these large protein molecules do pass through the filters and into the urine to be eliminated.

Proteinuria has no symptoms early in its course. One of the earliest signs of proteinuria is the foamy appearance of urine in the toilet. This foamy appearance is caused by the abnormally high amount of protein. As the disorder progresses, the symptoms progress to the development of edema (an accumulation of fluid causing swelling). As a result of the loss of protein from the bloodstream, less fluid is carried in the bloodstream, with more remaining in the tissues. As a result, edema appears in the hands and/or the feet and in the abdominal area.

Treatment and Therapy

The diagnosis of proteinuria is made based on the collection of urine samples. In the past, it required the collection of a twenty-four-hour urine specimen, with the diagnosis of proteinuria being made if more than 150 milligrams of protein were excreted per day. More recently, the diagnosis of proteinuria has been made based on one urine sample by determining a urine albumin (protein) to creatinine (waste product) ratio. More than 30 milligrams of albumin per milligram of creatinine is indicative of proteinuria. Whenever proteinuria is present, additional tests of kidney function are indicated. Chronic proteinuria is often indicative of chronic kidney disease.

Treatment of proteinuria is dependent on treating the underlying problem. Dietary modifications may be made to control glucose, sodium, and protein intake. Medications may be used to treat diabetes and hypertension. The most commonly used medications are angiotensin-converting enzyme (ACE) inhibitors. Diuretics may be used as well in order to help the kidneys eliminate excess fluid.

Perspective and Prospects

Proteinuria was first alluded to, although unnamed, by Hippocrates around 400 b.c.e. when he described bubbly urine as a symptom of kidney disease. Over the next two thousand years, there were multiple allusions to foaming urine in the scientific and medical literature, indirectly linking it to kidney disease and to dropsy (tissue swelling because of retention of excessive amounts of fluid). In 1814, an English physician, John Blackall, published a book on dropsy in which he directly established a link between that condition and proteinuria (using the actual term). Shortly thereafter, fellow English physician Richard Bright published Reports of Medical Cases (1827), in which he identified edema and proteinuria as the major symptoms of nephritis
(inflammation of the kidney, also known as Bright’s disease). Since that time, proteinuria has been considered to be an early and major symptom of kidney disease.

Bibliography

Brenner, Barry M., ed. Brenner and Rector’s The Kidney. 9th ed. Philadelphia: Saunders/Elsevier, 2012.

Glassock, R. J. “Focus on Proteinuria.” American Journal of Nephrology 10, suppl. 1 (1990): 88–93.

"Proteinuria." National Kidney and Urologic Diseases Information Clearinghouse, September 2, 2010.

Strasinger, Susan J., and Marjorie Schaub Di Lorenzo. Urinalysis and Body Fluids. 5th ed. Philadelphia: F. A. Davis, 2008.