Interviewer: An estimated 3.83% of adults aged 20 or older -- that's about 7.7 million Americans -- have physiological evidence of chronic kidney disease. Dr. Narva explains that chronic kidney disease is defined in two ways.

Dr. Narva: One is a decrease in the filtering ability of the kidney. The kidney is a filter and when you've lost about half of your filtering capacity you can be diagnosed as having chronic kidney disease. The second way of being diagnosed as having chronic kidney disease is if you have evidence of kidney injury, even if your kidney filters normally.

Interviewer: Most people have two kidneys. They're located near the middle of the back. Every day healthy kidneys filter about 200 quarts of blood and remove about two quarts of waste and extra water to make urine. But how do you know if your kidneys are functioning normally?

Dr. Narva: Kidney disease is often referred to as a "silent disease." It's said that it's silent because most people have no symptoms until their kidneys are very, very seriously injured. In other words, normally we have a lot of extra kidney capacity -- a lot of extra filtering capacity -- and you can lose half of that and not even be aware of it. You can loose three quarters of it and you may not be aware of it. In fact, many people don't become aware that they have kidney disease until just a relatively short time before they require dialysis. That's why it's very important for people to be screened early if they're at risk. So if you have heart disease, if you have high blood pressure, if you have diabetes, if you have anyone in your family with kidney disease, you should be screened and the screening is very simple.