Cholestasis is defined as a decrease in bile flow due to impaired secretion by hepatocytes or to obstruction of bile flow through intra-or extrahepatic bile ducts. Therefore, the clinical definition of cholestasis is any condition in which substances normally excreted into bile are retained. The serum concentrations of conjugated bilirubin and bile salts are the most commonly measured.
Not all substances normally excreted into bile are retained to the same extent in various cholestatic disorders. In some conditions, serum bile salts may be markedly elevated while bilirubin is only modestly elevated and vice versa. However, demonstrable retention of several substances is needed to establish a diagnosis of cholestasis. Only in rare disorders of bilirubin metabolism (eg, Dubin-Johnson syndrome, Rotor syndrome) does an isolated increase in the serum concentration of conjugated bilirubin appear, so increased serum conjugated bilirubin indicates cholestasis. The histopathologic definition of cholestasis is the appearance of bile within the elements of the liver, usually associated with secondary cell injury.