Laboratory determinations that reflect liver disease are commonly termed liver function tests. This is a misnomer because, for example, elevated serum aminotransferase and alkaline phosphatase activities are not indices of the degree of liver dysfunction but are only markers of liver injury. Even measures of specific hepatic functions, such as the serum albumin concentration, bilirubin concentration, and prothrombin time, can be affected by extrahepatic factors, such as nutritional state, hemolysis, and antibiotic use. Nevertheless, for the sake of discussion, the term liver function tests is used in this article to denote the battery of screening tests routinely available in most clinical laboratories, including serum aspartate (AST) and alanine (ALT) aminotransferase, serum alkaline phosphatase, serum total and direct bilirubin, serum total protein (with albumin and globulin fractionation), and prothrombin time. Beyond this minor semantic point, the evaluation of the patient with abnormal liver function tests is further complicated by the relative lack of well-defined diagnostic algorithms. Instead a systematic evaluation of the patient with abnormal liver function tests requires an understanding of the distinct patterns that the liver exhibits in response to injury as well as a working knowledge of the common liver disorders that present with a particular injury pattern. Once nonhepatic causes for any observed abnormalities are excluded(Table 1), the evaluation is facilitated by classification of liver injury into four major patterns: cholestatic, hepatocellular, immunologic, and infiltrative disease. Immunologic injury can present with either a cholestatic picture (if the bile ducts are the target of the immune response, as in primary biliary cirrhosis [PBC]) or a hepatocellular pattern of injury (if the hepatocyte is the primary target, as in viral and autoimmune hepatitis). The typical liver function test abnormalities seen in these types of liver injury are listed inTable 2. Although the rationale is provided subsequently during discussions of specific disorders, additional laboratory evaluation of any patient with prolonged elevation of serum aminotransferases, consistent with hepatocellular injury, most often should include the following:

In contrast, the initial step in the evaluation of the patient with cholestatic indices (i.e., elevated serum alkaline phosphatase and bilirubin levels, with or without moderate elevations in serum ALT or AST) should be abdominal ultrasonography to assess the bile ducts, gallbladder, liver, and pancreas. An elevated serum bilirubin level in the absence of elevations in serum alkaline phosphatase or AST levels suggests underlying cardiac disease more than hepatobiliary disease.<sup>14 Brown A.N., Scheiner L.B., Cohen S.N. Evaluation of bilirubin in a liver screening panel [letter] JAMA 1992 ;  268 : 1542

Cliquez ici pour aller à la section Références</sup> Isolated elevation of serum alkaline phosphatase, confirmed by serum leucine aminopeptidase (LAP), 5′-nucleotidase (5′-NT), or gamma-glutamyltranspeptidase (GGTP) to be hepatic in origin, is strongly suggestive of an infiltrative process, whether a localized or systemic granulomatous disorder or metastatic carcinoma to the liver. An approach to the patient with an elevated alkaline phosphatase level is proposed inFigure 1.