The Renal Excretion of Endogenous Creatinine in Man. Comparison With Exogenous Creatinine and Inulin

The study of the renal excretion of creatinine has been concerned hitherto largely with exo- genous creatinine because of difficulties in the determination of endogenous plasma creatinine. Behre and Benedict (1) and others (2, 3) have denied the presence of any appreciable amount of creatinine in normal plasma. On the other hand several authors have reached the opposite conclusion (4, 5, 6). To avoid this controversy investi- gators of the renal excretion of creatinine have administered creatinine orally or intravenously to raise the concentration in plasma to levels much above that of the " endogenous chromogenic substance."' In this way it is possible to obtain values for exogenous creatinine which are not appreciably influenced by the color development of the endogenous Jaffe-reactive material. This technique was employed by Rehberg (7) when he suggested the creatinine clearance as a measure of the true glomerular filtrate in the human kidney. He gives by mouth 5 grams of creatinine one hour before the test. The Rehberg technique has been so widely employed in physiological and clinical studies that it has become universally known as simply the "creatinine" rather than the " exo- genous creatinine " clearance.