What is proteinuria?
Kidneys are constantly filtering blood. Thousands of tiny filters (glomeruli) in each kidney know what should stay in the blood and what should pass through as urine. If too much protein gets into your child’s urine, it is called proteinuria.
What is nephrotic syndrome?
When too much protein leaves the blood and goes into urine, the level of protein in the blood gets too low. When this happens, some of the fluid that makes up the blood leaks into the tissues, causing parts of the body to swell. This is called the nephrotic syndrome.
What causes proteinuria and nephrotic syndrome?
In most cases, the cause of protein leaking into urine is unknown. Sometimes a child can be born with a very rare kidney disease that causes high amounts of protein in the urine; this is likely diagnosed shortly after birth. But the more common findings of proteinuria can occur at any time and age, and the majority of cases are mild and unnoticed by the person who has it.
Anybody can get nephrotic syndrome, and like all forms of proteinuria, there is no known cause. 85% of children with nephrotic syndrome have something called minimal change disease, which means that if one were to take a sample of the kidney (called a kidney or renal biopsy), the filters look nearly normal and protein loss responds well to treatment. Since 85% is a large portion of cases, minimal change disease is suspected most of the time.
Cases with abnormal filter patterns are known as focal segmental glomerulosclerosis, mesangial nephropathy and membranous nephropathy. They are more serious, and in some cases a decrease in kidney function may occur. If these conditions are suspected, a kidney biopsy may be needed. Nephrotic syndrome can occur in other conditions as well, for example severe glomerulonephritis, and response to treatment will vary.