CLEARANCE TESTS OF LIVER-FUNCTION

A study of the clearance of test substances removed from the circulation primarily by the liver provides the most sensitive and reliable index to the functional capacity of the liver. Clearance studies should be used to detect early phase or subclinical liver disease and monitor the recovery of liver injury. A test substance which is non-noxious should be selected and given in a dose which approaches its maximal removal capacity (Vmax). Indocyanine green clearance (5.0 mg per kg) provides a simple sensitive measure of liver function, with the advantage of evaluating removal by dichromatic ear densitometry. A study of the capacity to remove endogenous or exogenous bile acids by measuring serum bile acids with radioimmunoassay provides a promising alternative to indocyanine green clearance. A variety of exogenous substrates, including galactose, protein, and aminopyrine, are available for loading tests. Patients without clinical features of liver disease and normal serum enzymes customarily used to evaluate liver function may have significant liver disease. Such disease is best recognized by clearance tests which should be used to determine the specificity of increased enzyme activity, detect lesions not reflected in abnormalities of serum enzymes, and determine when recovery has occurred in reversible liver disease.