Relation of Creatinine Excretion in Urine to Plasma Creatinine Concentration

Abstract

Following the administration of creatinine to normal rabbits during a copious diuresis, under conditions most apt to lead to full renal activity, the rate of creatinine excretion in the urine has been found to be directly proportional to the plasma creatinine concentration. A similar relationship has been found in man. Typical examples are presented in Fig. 1. The large difference in the values of the ratios: Urine rate/Plasma concentration is undoubtedly due, as in the case of urea, 1 to the different amounts of renal tissue possessed by man and the rabbit. Under the same conditions urea behaves in a like manner 2 although the urine rate for a given plasma concentration is always greater for creatinine. That is, the excretory ratio Urine rate/Plasma concentrationp is less for urea. The significance of this will be discussed elsewhere. Since the difference between the ratios for these 2 substances appears to bear a constant relation to the lower it is obvious that creatinine may be substituted for urea in measuring renal function by Addis' method. 3 Rehberg 4 has used creatinine in what is essentially this method but failed to observe the standard or other constant conditions and obtained inconstant results. He found 5 only a general tendency for the urine rate to increase in proportion to the plasma concentration. An examination of the method using creatinine under more rigid conditions is now in progress.