The Clinical and Comparative Value of Renal Function Tests
Renal function has to do in general terms with the preservation and maintenance of an optimum environment for body cells. In the unicellular organism where the entire body is in contact with its environment, the process of excretion is a simple matter of diffusion, but in multicellular body masses it becomes necessary that certain specialized cells excrete the waste products of metabolism, excessive water, and salts in order that the chemical composition of the body fluid and cells may remain constant. Specifically, the kidney excretes the waste products of nitrogen metabolism and the excessive inorganic salts, exercising, however, a certain amount of selective action in regard to those salts necessary for the animal economy and excreting others which have no threshold in toto. Therefore, these functions are of prime importance in maintaining the viscosity or tonicity of the blood and body fluids and are directly concerned in the maintenance of the hydrogen ion concentration of the body within the narrow limits of fluctuation consistent with health. The kidney undoubtedly acts in accordance with nervous and probably hormonal influences and is profoundly affected by disturbances of endogenous metabolism in other portions of the body. Metabolic disturbances incident to general infections of the body and surgical operations increase the renal load and may be factors which cause insufficiency. Thus some method which will be an index of renal reserve is highly desirable.
It is hardly conceivable that any single ideal test for renal function, especially in the diseased kidney, can ever be. . .