The Value of the Urea Clearance Test
Renal function has to do with the maintenance of the normal constitution of the body fluid—in other words, with the preservation of an optimum internal environment for the body cells. The kidney, in excreting an excess of water with the end-products of nitrogenous metabolism, must exercise a certain degree of discrimination in regard to the excretion of inorganic salts and other so-called threshold substances, depending upon the body need. The importance of such a basic function renders necessary the development of accurate methods for the estimation of renal efficiency. It is not to be expected that any one simple test can be used as an accurate index of the efficiency of an organ whose task involves multiple processes and whose function is influenced from without through nervous connections and hormone control.
Certain phases of renal activity have been used as a basis for tests which may grossly be classified as excretion and retention tests. Excretion tests may be subdivided into (1) those which utilize the estimation of substances normally excreted, and (2) those in which a foreign substance is employed in making the test. The former includes the water test, concentration and dilution test, Mosenthal test, the creatinine test of Major, the urea concentration test of MacLean and the urea clearance test of Van Slyke. The tests in which a foreign substance is employed include the phenolsulphonphthalein test of Geraghty and Rowntree, the indigo-carmine and all dye tests. In retention tests, an estimation is made of the level in. . .