UREA CLEARANCE AND DIURESIS IN MAN

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Abstract
The relation of the urea clearance (C) to diuresis (v) has been re-examined in 1 normal subject and in 3 nephrosclerotics. The clearance rises continuously with diuresis at all diureses. The quantitative relation can be represented by the equation (C = A(1[long dash]e-kv)+bv, where A, b and k are constants, and e is the base of natural logarithms. In all 4 examples b is significantly different from zero. In renal disease both A and k diminish, although not proportionately, whereas b does not diminish and may increase. A pathological clearance cannot therefore be expressed in % of another clearance, except at a specified urine flow. The clearance and the conc. ratio of urea are equivalent and mutually interchangeable at all diureses. The conc. ratio approaches a limit as diuresis approaches zero. This limiting conc. ratio, equal numerically to the initial slope of the clearance curve, is a most sensitive index of urea excretion. The correspondence between the clearance and the concentration ratio proves that in comparing the concentration tests of renal function with the clearance, both the sp. gr. of the urine and the clearance (or its equivalent, the conc. ratio) should be compared at the same diuresis. Since the urea conc. in the urine is not less than that of the blood, the conc. ratio at large diuresis and therefore the constant b should not be less than 1. In all examples given, b is larger than 1.

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