Nephrotic syndrome is not a disease itself. It is a set of signs and symptoms that indicate another disease has damaged the kidneys’ filtering system and they are no longer working properly. Nephrotic syndrome is a condition marked by very high levels of protein in the urine; low levels of protein in the blood; swelling, especially around the eyes, feet, and hands especially in the abdomen (ascites); and high cholesterol. Nephrotic syndrome results from damage to the kidneys’ glomeruli (the singular form is glomerulus). Glomeruli are tiny blood vessels that filter waste and excess water from the blood and send them to the bladder as urine.
Blood is ‘cleaned’ in the kidneys as it passes through tiny filters called nephrons. Each kidney contains about one million nephrons. The kidneys remove waste products from the blood (such as uric acid), while maintaining a balance of nutrients, salts and water.
Normally, protein is not removed when the kidneys filter waste from the blood. However, when the kidneys are damaged, protein leaks through the damaged filters and is removed from the body in the urine, along with the waste products. The two proteins that are most likely to be present in the urine when this happens are albumin (controls blood volume) and globulin (largely made up of antibody proteins).
When the protein level in the blood drops, liquid seeps out of the smallest blood vessels (capillaries) all over the body and settles into the surrounding tissue, causing fluid swelling (oedema).
Normally a person loses less than 150mg of protein in the urine in a 24-hour period. A person with nephrotic syndrome can lose more than 3.5g of protein in the urine during a 24-hour period or 25 times the normal amount.