What are kidneys?
Kidneys are fist-sized organs located on the back of your body, just beneath the bottom of your ribcage. They are oval-shaped with a dimple where the blood vessels run in and out. They are shaped a lot like kidney beans and are a similar dark red color. Most people are born with two kidneys.
What do the kidneys do?
The kidneys filter all the blood in your body, getting rid of waste products and extra fluid, which then leave the body as urine. This helps to control your blood pressure. The kidneys also tell your body when to make more red blood cells. These red blood cells deliver oxygen to all the different parts of the body. Finally, your kidneys produce an active form of vitamin D that helps your bones stay strong.
How is kidney function measured?
Kidney function is often measured using estimated glomerular filtration rate, or eGFR. This is usually calculated based on the level of creatinine in your blood, as well as characteristics such as your sex, race, and age. When a doctor wants to measure your eGFR, they are are trying to measure how well your kidneys are filtering your blood. There are more invasive tests to measure your kidney function, but these are not used as often.
How does kidney function change over time?
In all people, including those who donate a kidney and those who do not, kidney function declines over time. How fast kidney function declines varies from person to person depending on lifestyle choices (e.g. how much salt you eat), race, sex, and family history of kidney disease. Doctors worry when your eGFR gets too low, because that indicates that your kidneys aren’t filtering your blood as well as they should.
The most common causes of low kidney function in the United States are diabetes and high blood pressure (hypertension). At the end of 2013, more than 600,000 people in the United States had end-stage renal disease, or kidney failure. When a person has end-stage renal disease, waste products build up in their blood to dangerous levels. To clear these waste products out of their blood, a person can either go on dialysis or get a kidney transplant. Dialysis uses a machine to filter the extra fluid and waste out of a person’s body, while a kidney transplant gives the recipient a functioning kidney. People on the most common form of dialysis, called hemodialysis, usually need to have their blood filtered by the machine for about 12 hours per week. People who stay on dialysis also don’t live as long as people who get a kidney transplant.