Creatinine blood test: A test that helps determine whether the kidneys are functioning normally. The kidneys maintain the blood creatinine in a normal range. Creatinine has been found to be a fairly reliable indicator of kidney function.

As the kidneys become impaired for any reason, the creatinine level in the blood will rise due to poor clearance by the kidneys. Abnormally high levels of creatinine thus warn of possible malfunction or failure of the kidneys. It is for this reason that standard blood tests routinely check the amount of creatinine in the blood. A more precise measure of the kidney function can be estimated by calculating how much creatinine is cleared from the body by the kidneys and it is referred to creatinine clearance.

"Creatinine" is derived from the Greek word "kreas," meaning "flesh." The suffix "-ine" denotes a chemical substance.