The nephrotic syndrome is caused by renal diseases that increase the permeability across the glomerular filtration barrier. It is classically characterized by four clinical features, but the first two are used diagnostically because the last two may not be seen in all patients:
- Nephrotic range proteinuria — Urinary protein excretion greater than 50 mg/kg per day
- Hypoalbuminemia — Serum albumin concentration less than 3 g/dL (30 g/L)
The term nephrotic syndrome refers to a group of symptoms that occur in people with kidney (renal) disease.
- High levels of protein (albumin) in the urine
- Low levels of the protein (albumin) in the blood
- Swelling (also called edema) of the face, legs, or ankles due to the abnormal collection of fluids in the tissues
Nephrotic syndrome develops when there is damage to the glomeruli, the structures in the kidneys that work to filter the blood (figure 1). This damage allows proteins in the blood (such as albumin) to leak into the urine, causing proteinuria. (See "Patient information: Protein in the urine (proteinuria)".) Eventually, blood levels of albumin become reduced. Reduced kidney function leads to accumulation of fluid in the tissues (edema).
Urine has a frothy appearance woing to yhe high protein content ( losses greater than 3.5 g in 24h) and a consequence hypoalbuminaemia develop. The loss of immunoglobulins increase the risk of infection.
The normal value of plasma total proteins is 60-80 gL-1.
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.
Once nephrotic syndrome is established, the doctor may recommend a kidney biopsy: a procedure in which tiny pieces of the kidney are obtained via ultrasound guidance 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 biopsyis rarely necessary.
Doctors investigate the possibility of acute glomerulonephritis in people whose laboratory test results indicate kidney dysfunction or blood in the urine and in people who develop symptoms of the disorder, particularly those who have had strep throat or other infections. Laboratory tests show variable amounts of protein and blood cells in the urine and often kidney dysfunction, as shown by a high concentration of urea and creatinine (waste products) in the blood.
In people with rapidly progressive glomerulonephritis, casts (clumps of red blood cells or white blood cells) are almost always visible in a urine sample that is examined under a microscope. Blood tests detect anemia and often an abnormally high number of white blood cells. When doctors suspect glomerulonephritis, a biopsy of the kidney is usually done to confirm the diagnosis, help determine the cause, and determine the amount of scarring and potential for reversibility. Kidney biopsy is done by inserting a needle in one of the kidneys under ultrasound or computed tomography (CT) guidance to obtain a small amount of kidney tissue. Although kidney biopsy is an invasive procedure and occasionally can become complicated, it is usually safe.
Additional tests are sometimes helpful for identifying the cause. For example, a throat culture may provide evidence of streptococcal infection. Blood levels of antibodies against streptococci may be higher than normal or progressively increase over several weeks. Acute glomerulonephritis that follows an infection other than strep throat is usually easier to diagnose, because its symptoms often begin while the infection is still obvious. Cultures and blood tests that help identify the organisms that cause these other types of infections are sometimes needed to confirm the diagnosis.
The nephrotic syndrome refers to clinical complex that includes the following
1 massive proteinuria, with daily protein loss in the urine of 3.5 gm or more in adults.