Your kidneys are 2 bean-shaped organs about the size of a fist, located near the middle of the back, below the rib cage. Kidneys filter blood by keeping compounds that are useful and removing waste and excess fluid, and they help regulate blood pressure and the number of red blood cells. Every 30 minutes, your kidneys filter all the blood in your body. The February 11, 2009, issue of JAMA includes an article about dietary phosphorus intake among patients with end-stage kidney disease. This Patient Page is based on one published in the December 12, 2001, issue of JAMA.