Creatinine Excretion in Renal Failure.∗

Summary and Conclusions 1. The urinary excretion of creatinine decreases as the filtration rate falls and the serum creatinine rises in chronic renal failure. This is especially apparent when the serum creatinine exceeds 6 mg/100 ml. 2. This decrease is due to either a reduced rate of creatinine production or an alternate excretory pathway. The muscle mass is not significantly decreased, and therefore should not account entirely for decreased production. Alternative excretion in the urine as creatine, or in the feces as creatinine is excluded by the data presented. Other possible mechanisms are suggested, but have not been studied.