What is nephrotic syndrome?
Nephrotic syndrome is a condition marked by
- very high levels of protein in the urine, a condition called proteinuria
- low levels of protein in the blood
- swelling, especially around the eyes, feet, and hands
- high cholesterol
What causes nephrotic syndrome?
Nephrotic syndrome results from damage to the kidneys' glomeruli—tiny blood vessels that filter wastes and excess water from the blood and send them to the bladder as urine.
When the glomeruli are working properly, they keep protein in the blood from leaking into the urine. Healthy kidneys allow less than 1 gram of protein to escape through the urine in a day. In nephrotic syndrome, the damaged glomeruli allow 3 grams or more of protein to leak into the urine during a 24-hour period.
As a result of this protein loss, the blood is deficient. Normal amounts of blood protein are needed to help regulate fluid throughout the body. Protein acts like a sponge to soak up fluid into the bloodstream. When blood is low in protein, fluid accumulates in the body’s tissues rather than circulating. The fluid causes swelling and puffiness.
Nephrotic syndrome can occur with many diseases. In adults, the most common causes are diabetic nephropathy and membranous nephropathy. In older adults, the most common cause is amyloidosis. Prevention of nephrotic syndrome relies on controlling these diseases. Frequently, however, the cause of nephrotic syndrome is unknown.
How is nephrotic syndrome diagnosed?
Your doctor will need blood and urine samples to evaluate your condition.
A high level of protein in a spot urine sample may indicate nephrotic syndrome. The doctor may order a 24-hour collection of urine in order to get a more precise measurement.
Blood tests may show low levels of protein. If kidney damage is advanced, waste products such as creatinine and urea nitrogen may build up in the blood.
Once nephrotic syndrome is established, the doctor may recommend a kidney biopsy—a procedure in which tiny pieces of the kidney are removed for examination with a microscope. The biopsy may reveal the underlying disease so that the doctor can determine a course of treatment. If a person has had diabetes for some time, and the patient history and laboratory tests are consistent with diabetic nephropathy, a biopsy is rarely necessary.
How is nephrotic syndrome treated?
In addition to addressing the underlying cause, treatment of nephrotic syndrome focuses on reducing high cholesterol, blood pressure, and protein in urine through diet, medications, or both. Two groups of blood pressure medications—angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs)—also protect the kidneys by reducing proteinuria.
Some people may benefit from limiting protein in their diet to reduce the buildup of wastes in the blood.
Nephrotic syndrome may go away once the underlying cause, if known, has been treated. In children, 80 percent of cases of nephrotic syndrome are caused by a condition called minimal change disease, which can be successfully treated with prednisone. However, in adults, most of the time the underlying cause is a kidney disease such as membranous nephropathy or focal segmental glomerulonephritis, diseases that are treated with corticosteroids, immunosuppressive drugs, and, in some cases, cytotoxic agents. Unfortunately, these treatments do not always bring about remission of nephrotic syndrome. Depending on the disease, as many as half of the patients may develop chronic kidney disease that progresses to end-stage renal disease. In these cases, the kidneys gradually lose their ability to filter wastes and excess water from the blood. If kidney failure occurs, the person will need dialysis or a kidney transplant.
National Kidney and Urologic Diseases Information Clearinghouse
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The National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC) is a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The NIDDK is part of the National Institutes of Health of the U.S. Department of Health and Human Services.
Established in 1987, the Clearinghouse provides information about diseases of the kidneys and urologic system to people with kidney and urologic disorders and to their families, health care professionals, and the public. The NKUDIC answers inquiries, develops and distributes publications, and works closely with professional and patient organizations and Government agencies to coordinate resources about kidney and urologic diseases.
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NIH Publication No. 07–4624