The main job of the kidneys is to remove wastes from the blood and return the cleaned blood back to the body.

Every minute, about one litre of blood (one fifth of all the blood pumped by the heart) enters the kidneys through the renal arteries. The blood then runs through tiny filtering units of the kidney, called nephrons.

Each kidney is made up of approximately one million nephrons. The nephrons either save substances the body needs (to be carried by the renal veins back to the body's cells) or they eliminate excess nutrients, water and waste products, as urine. The ureters carry the urine from the kidneys to the bladder where it is stored until you urinate. Urine passes out of the body through a tube called the urethra.

Chronic kidney disease (CKD) is defined as the presence of kidney damage, or a decreased level of kidney function, for a period of three months or more. CKD can be divided into five stages, depending on how severe the damage is to the kidneys, or the level of decrease in kidney function.

Usually, kidney disease starts slowly and silently, and progresses over a number of years. Not everyone progresses from Stage 1 to Stage 5. Stage 5 is also known as End-Stage Renal Disease (ESRD). It may also be called end-stage renal failure. It is important to remember that end-stage refers to the end of your kidney function (your kidneys are working at less than 15% of normal), not the end of your life. To sustain life at this stage, dialysis or kidney transplantation is needed.