The word renal refers to the kidneys. The terms renal function and kidney function mean the same thing.

People with two healthy kidneys have 100 percent of their kidney function. Small or mild declines in kidney function – as much as 30 to 40 percent – would rarely be noticeable.

Some people are born with only one kidney but can still lead normal, healthy lives.

Every year, thousands of people donate one of their kidneys for transplantation to a family member or friend.

For many people with reduced kidney function, a kidney disease is also present and will get worse. Serious health problems occur when people have less than 25 percent of their kidney function. When kidney function drops below 10 to 15 percent, a person needs some form of renal replacement therapy – either blood-cleansing treatments called dialysis or a kidney transplant – to sustain life.