Ordinarily the kidneys work very efficiently to cleanse the blood of waste products and retain the normal blood constituents - water, salts, and proteins. Nephrotic syndrome, or nephrosis, is a condition in which the kidneys leak protein out of the bloodstream and into the urine. The resultant low blood protein levels cause water to build up in the tissues and the child becomes quite puffy. It is in the majority of cases relatively benign and self-limited.
Steroids often produce rapid improvement.
Sometimes nephrosis is only part of a larger problem of inflammation of the kidney, and then favorable prognosis is more uncertain. Peritonitis is a concern in children with nephotic syndrome.