THE CONCENTRATION OF UREA IN THE BLOOD OF NORMAL INDIVIDUALS 1

Abstract

The concentration of urea may be determined more easily and with greater accuracy than that of any other non-protein nitrogenous constituent of the blood. We have shown elsewhere (1) that the blood urea concentration ordinarily increases little above its usual level until the amount of functioning renal tissue has been reduced by more than half. Since a decreased renal function is not of immediate importance to the patient until such a degree (50 per cent) of reduction in the renal substance has taken place, the concentration of urea in the blood becomes an excellent clinical index of renal failure. An increase in the blood urea concentration above the normal range is then of great importance. The small number of subjects in the various series which have been published and the disparity of the results obtained have led us to collect further data relating to the blood urea concentration of normal individuals. In figure 1 the series of normal blood ureas which have been reported in the literature are briefly summarized. Only those groups of observations which were obtained, with two exceptions, from ten or more normal subjects and in which a reasonably reliable blood urea method was used have been included. The earlier and less reliable figures have been summarized by Schwartz and McGill (7). An examination of figure 1 shows a large degree of variation between the "normal range" and the mean values of the different groups of observations. Moreover the number of observations in any single series is too small to draw any conclusions of a general nature. 'This work was aided by the Wellington Gregg Fund for the Investigation of Bright's Disease. 295