UREA EXCRETION AT LOW URINE VOLUMES. THE CALCULATION OF “MINIMAL” UREA CLEARANCES

Abstract

Series of hourly urea clearance determinations were done in normal and diseased adults who were made oliguric by water deprivation. In all cases, the clearances (U V/B) varied linearly and quantitatively with the urine vol. (V), at all vols. below about 0.35 ml. per min. This means that the urea conc. ratio (U/B) in any series is constant for this range of urine vols. Since the conventional calculations of maximal or standard urea clearances do not give a constant, it is proposed that "minimal" clearances be calculated for this range of urine volumes. The U/B being the same at 0.35 ml. per min. as at any lower volume, one calculates what the clearance would be at a urine volume of 0.35 ml. per min. The actual vol. output is disregarded, and the calculation is made with V = 0.35 ml. When the "minimal" clearance is expressed in %, the U/B is multiplied by 1.11. Taking as controls the valid standard and maximal urea clearances observed in series with "minimal" clearances, one finds satisfactory agreement between the control and "minimal" clearances. In 241 such calculations, where the control is 100%, the mean "minimal" clearance is 96.3 with a standard deviation of 15.18.