Comparison of Endogenous and Exogenous Creatinine Clearances in Man. ∗

Abstract

Summary

Nine normal individuals and 6 patients with varying levels of renal insufficiency were given intravenous infusions of creatinine. The endogenous creatinine clearance:inulin clearance ratio in the normal subjects was 1.11. The ratio of the exogenous creatinine clearance to inulin clearance rose quickly to 1.73 as soon as the creatinine infusion was started, then gradually fell to 1.40 after ninety minutes of infusion. The patients with renal insufficiency had an initial ratio of 1.50 and a late rise to 1.71 after ninety minutes. It seems most likely that a small increment in the serum creatinine concentration can cause an increased effectiveness of the tubular mechanism for creatinine secretion. An alteration in the serum creatinine resulting in enhanced tubular transport, or reducing apparent serum creatinine concentration without affecting filtration, is less probable. The high pre-infusion ratio in patients with renal insufficiency, and the failure to respond to exogenous creatinine, suggests that the mechanism for increased tubular excretion may continue to function as long as the stimulus of an elevated serum creatinine persists.