COMPARISON OF THE CONSTANT INFUSION AND URINE COLLECTION TECHNIQUES FOR THE MEASUREMENT OF RENAL FUNCTION 1

Abstract

For any exogenous substance which is neither metabolized, stored nor excreted otherwise than in the urine, the rate of excretion must be equal to the rate of infusion under conditions where its plasma level and volume of distribution are constant. A method for the measurement of glomerular filtration rate (GF), renal plasma flow (PF) and tubule excretory capacity (TmPAH) based upon this principle is described. In the application of the prin-ciple, the rate of infusion (IV) of the test substance is substituted for the rate of excretion (UV) in the clearance formula: UV/P=C. The procedure obviates the necessity of bladder catheterization. Good correlation between this technique and the usual urine collection technique was obtained in 45 expts. for GF, 26 expts. for PF, and in 10 expts. for TmPAH. Unsuccessful attempts resulted from failure to attain equilibrium between rates of infusion and excretion, especially in the presence of edema. The IV technique may be erroneous in short expts. in subjects whose renal function clearances are less than 60% of normal. The IV technique clearances reflect acute changes in renal function, but are damped in magnitude.