STUDIES OF UREA EXCRETION. IX. COMPARISON OF UREA CLEARANCES CALCULATED FROM THE EXCRETION OF UREA, OF UREA PLUS AMMONIA, AND OF NITROGEN DETERMINABLE BY HYPOBROMITE

Abstract

Expts. with human subjects show that when the proportion of urea in the urea + ammonia mixture of the urine is markedly decreased by induced acidosis and low protein diet, the urea clearances calculated from the excretion rate of urea alone suffer a parallel reduction. If, however, values for excretion of urea + ammonia are substituted for urea, the clearances calculated remain at the usual levels. The theoretical significance of the results is to favor the hypotheses, that the ammonia excreted in the urine of man is formed in the kidneys chiefly from urea removed from the blood, and that the work of the kidneys in excreting urea from the blood is more accurately indicated by the combined excretion of urea and ammonia than by the excretion of urea alone. The practical deduction is that in determinations of the urea clearance as a measure of renal function, results are somewhat more consistent if in the clearance formula, UV/B or U(Vi)/B, one uses for U the urinary concn. of urea + ammonia N, instead of only urea N. When the urinary urea is detd. by methods measuring the NH3 formed by urea hydrolysis, or the N2 yielded by the action of hypobromite, the determination of combined urea + ammonia N is also simpler than determining the urea N separately. The routine procedure developed for clinical determination of the urea clearance is described.