Answer: Most people have two kidneys, which are vital organs that filter waste from the body and create urine. They also balance electrolytes in the body and play a role in maintaining blood pressure and blood volume.
Some people hardly notice when their kidneys stop working properly, Denny said. Others, he said, get quite ill.
"Half the patients will not feel well," he said. "They will get swollen legs and have fatigue, or not feel well and see the doctor. And the doctor will say, 'Hey, you have a kidney problem.'
"The other half of patients will feel nothing until the kidneys are almost gone. And they'll just get a physical ... and realize that the creatinine in their blood, which is a measure of kidney function, has increased.
"A lot of people don't feel anything at all, which is troubling because they don't always believe they have kidney problems. ... Those people will often have some chronic disease that they either have not managed well or has been really severe. You don't really feel hypertension and diabetes, and so sometimes they don't do anything about it."
Most people only need one functioning kidney to live a healthy life. That allows people to donate a kidney to a person with kidney disease.
Q: What causes kidney disease?
A: Hypertension and/or diabetes are the root causes for about half of all people with end-stage renal disease, Denny said. That's especially true among people in the African American population.
Other conditions, such as cystic kidneys, genetic factors, nephrotic syndrome and autoimmune diseases also can cause kidney failure.
Not all kidney failure is permanent. But for those who have end-stage renal disease, and whose kidneys are not functioning, they will either need dialysis to artificially filter the blood or they'll need a kidney transplant.