Nephrotic syndrome occurs when the filters in the kidney leak an excessive amount of protein. The level of protein in the blood then falls and this allows fluid to leak across very small blood vessels into the tissues. Swelling around the eyes, abdomen and legs is a consequence of this process.

The primary degenerative effect in nephrotic syndrome is in the capillary basement membrane of the glomerulus. As the degeneration continues the kidney tissue pore size increases to allow the passage of protein into the filtrate. The disease is characterised by proteinuria (Excessive protein especially albumin in the urine), low blood protein and oedema(swelling in the tissues). Protein losses in the urine are commonly 5-10gms per day but may also exceed 30gms per day.