What the Kidneys Do You have two kidneys. They are bean-shaped and about the size of a fist. They are located in the middle of your back, on the left and right of your spine, just below your rib cage. The kidneys filter your blood, removing wastes and extra water to make urine. They also help control blood pressure and make hormones that your body needs to stay healthy. When the kidneys are damaged, wastes can build up in the body. Kidney Function and Aging Kidney function may be reduced with aging. As the kidneys age, the number of filtering units in the kidney may decrease, the overall amount of kidney tissue may decrease, and the blood vessels that supply the kidney may harden, causing the kidneys to filter blood more slowly. If your kidneys begin to filter less well as you age, you may be more likely to have complications from certain medicines. There may be an unsafe buildup of medicines that are removed from your blood by your kidneys. Also, your kidneys may be more sensitive to certain medicines. For example, nonsteroidal anti-inflammatory drugs (NSAIDs) and some antibiotics may harm your kidneys in some situations. The next time you pick up a prescription or buy an over-the-counter medicine or supplement, ask your pharmacist how the product may affect your kidneys and interact with your other medicines. (Watch the video to learn more about what the kidneys do. To enlarge the video, click the brackets in the lower right-hand corner. To reduce the video, press the Escape (Esc) button on your keyboard.) Learn more about how the kidneys work.  How Kidney Disease Occurs Kidney disease means the kidneys are damaged and can no longer remove wastes and extra water from the blood as they should. Kidney disease is most often caused by diabetes or high blood pressure. According to the Centers for Disease Control and Prevention, more than 20 million Americans may have kidney disease. Many more are at risk. The main risk factors for developing kidney disease are - diabetes   - high blood pressure   - cardiovascular (heart and blood vessel) disease   - a family history of kidney failure. diabetes high blood pressure cardiovascular (heart and blood vessel) disease a family history of kidney failure. Each kidney contains about one million tiny filtering units made up of blood vessels. These filters are called glomeruli. Diabetes and high blood pressure damage these blood vessels, so the kidneys are not able to filter the blood as well as they used to. Usually this damage happens slowly, over many years. This is called chronic kidney disease. As more and more filtering units are damaged, the kidneys eventually are unable to maintain health. Early kidney disease usually has no symptoms, which means you will not feel different. Blood and urine tests are the only way to check for kidney damage or measure kidney function. If you have diabetes, high blood pressure, heart disease, or a family history of kidney failure, you should be tested for kidney disease. Kidney Failure  Kidney disease can get worse over time, and may lead to kidney failure. Kidney failure means very advanced kidney damage with less than 15% normal function. End-stage renal disease (ESRD) is kidney failure treated by dialysis or kidney transplant. If the kidneys fail, treatment options such as dialysis or a kidney transplant can help replace kidney function. Some patients choose not to treat kidney failure with dialysis or a transplant. If your kidneys fail, talk with your health care provider about choosing a treatment that is right for you. (Watch the video to learn more about how kidney disease progresses. To enlarge the video, click the brackets in the lower right-hand corner. To reduce the video, press the Escape (Esc) button on your keyboard.)