Signs and symptoms of nephrotic syndrome include:

• Severe swelling (edema), particularly around your eyes and in your ankles and feet
• Foamy urine, which may be caused by excess protein in your urine
• Weight gain due to excess fluid retention
• Fatigue
• Loss of appetite

Nephrotic syndrome is usually caused by damage to the clusters of tiny blood vessels (glomeruli) of your kidneys.

The glomeruli filter your blood as it passes through your kidneys, separating things your body needs from those it doesn't. Healthy glomeruli keep blood protein (mainly albumin) — which is needed to maintain the right amount of fluid in your body — from seeping into your urine. When damaged, glomeruli allow too much blood protein to leave your body, leading to nephrotic syndrome.

Many possible causes

Many diseases and conditions can cause glomerular damage and lead to nephrotic syndrome, including:

• Diabetic kidney disease. Diabetes can lead to kidney damage (diabetic nephropathy) that affects the glomeruli.
• Minimal change disease. This is the most common cause of nephrotic syndrome in children. Minimal change disease results in abnormal kidney function, but when the kidney tissue is examined under a microscope, it appears normal or nearly normal. The cause of the abnormal function typically can't be determined.
• Focal segmental glomerulosclerosis. Characterized by scattered scarring of some of the glomeruli, this condition may result from another disease or a genetic defect or occur for no known reason.
• Membranous nephropathy. This kidney disorder is the result of thickening membranes within the glomeruli. The exact cause of the thickening isn't known, but it's sometimes associated with other medical conditions, such as hepatitis B, malaria, lupus and cancer.
• Systemic lupus erythematosus. This chronic inflammatory disease can lead to serious kidney damage.
• Amyloidosis. This disorder occurs when substances called amyloid proteins accumulate in your organs. Amyloid buildup often affects the kidneys, damaging their filtering system.
• Blood clot in a kidney vein. Renal vein thrombosis, which occurs when a blood clot blocks a vein connected to the kidney, can cause nephrotic syndrome.

Factors that can increase your risk of nephrotic syndrome include:

• Medical conditions that can damage your kidneys. Certain diseases and conditions increase your risk of developing nephrotic syndrome, such as diabetes, lupus, amyloidosis and other kidney diseases.
• Certain medications. Examples of medications that can cause nephrotic syndrome include nonsteroidal anti-inflammatory drugs and drugs used to fight infections.
• Certain infections. Examples of infections that increase the risk of nephrotic syndrome include HIV, hepatitis B, hepatitis C and malaria.

Possible complications of nephrotic syndrome include:

• Blood clots. The inability of the glomeruli to filter blood properly can lead to loss of blood proteins that help prevent clotting. This increases your risk of developing a blood clot (thrombus) in your veins.
• High blood cholesterol and elevated blood triglycerides. When the level of the protein albumin in your blood falls, your liver makes more albumin. At the same time, your liver releases more cholesterol and triglycerides.
• Poor nutrition. Loss of too much blood protein can result in malnutrition. This can lead to weight loss, but it may be masked by swelling. You may also have too few red blood cells (anemia) and low levels of vitamin D and calcium.
• High blood pressure. Damage to your glomeruli and the resulting buildup of wastes in your bloodstream (uremia) can raise your blood pressure.
• Acute kidney failure. If your kidneys lose their ability to filter blood due to damage to the glomeruli, waste products may build up quickly in your blood. If this happens, you may need emergency dialysis — an artificial means of removing extra fluids and waste from your blood — typically with an artificial kidney machine (dialyzer).
• Chronic kidney disease. Nephrotic syndrome may cause your kidneys to gradually lose their function over time. If kidney function falls low enough, you may require dialysis or a kidney transplant.
• Infections. People with nephrotic syndrome have an increased risk of infections.