ABSTRACT
Renal clearance tests can provide important information about the effectiveness of the kidneys in carrying out their excretory function. Any endogenous or exogenous substance which is excreted by the kidney can be studied by the clearance approach. Specific foreign materials may be introduced into the body, and their concentration in blood may be measured along with urinary excretion in the study of clearance. The capacity of the kidney as an excretory organ is measured by three general functions: blood or plasma flow, filtration rate, and tubular transport. A clearance test involves the measurement of a constituent of the blood and also measurement of the amount of the same substance excreted in the urine during a specific interval of time. Determination of blood urea level was one of the first measures of renal function, and this measurement was employed as a routine clinical procedure at the beginning of the 20th century.
