Significantly high levels of protein in urine are always a sign of kidney disease.
The kidneys remove waste and excess water and salts from the blood. Kidneys receive blood through the renal arteries.
The blood flows into small, functional units of the kidney called nephrons. Each kidney contains millions of nephrons.
Each nephron is made of a glomerulus and a tubule.
The glomeruli filter the blood, removing waste products. They also prevent some substances, such as protein, from being taken out of the blood. If the glomeruli are damaged, protein from the blood leaks into the urine.
Normally, you should have less than 150 milligrams of protein in the urine per day. Having more than 150 milligrams per day is called proteinuria.