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Abnormalities in laboratory tests are frequently the first or only sign of liver disease, and the pattern of abnormality is often suggestive of the underlying disease process. Gamma-glutamyltransferase (GGT) is particularly sensitive for liver disease. If the level of GGT is normal, there is only a 1–2% chance of liver disease. The levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are also very useful for the diagnosis of liver disease. An AST > 3000 U/L suggests a severe hypotensive episode causing centrilobular necrosis, a toxic injury such as acetaminophen overdose, or acute viral hepatitis. On the other hand, chronic diseases of the liver such as alcoholic liver disease and chronic viral hepatitis are typically associated with smaller elevations of transaminases, in the 100–300 U/L range. Elevated ALT and AST with an AST/ALT ratio > 2:1 is classically associated with alcoholic hepatitis. Elevated alkaline phosphatase (ALP) can be seen in both liver and bone disease, whereas a concomitant elevation of ALP and GGT is consistent with cholestatic liver disease.

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While the above enzymes (GGT, AST, ALT and ALP) indicate damage to the hepatocytes, prothrombin time (PT) and serum albumin are more reflective of the functional status of the liver, since both albumin and clotting factors are produced by hepatocytes. Factor VII has a serum-half life of about 4 hours, making the PT a good assessment of an acute change in liver function, whereas albumin is more accurate at assessing a chronic change in liver function. Also, assessment of gamma globulins is useful for determining an acute versus chronic pathologic liver process. In acute processes, the gamma globulin level is normal, and in chronic processes, it is elevated (> 3 g/dL).

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When assessing liver function tests, four general patterns are apparent: (1) acute hepatitis pattern, which has elevated transaminase levels and variable increases in other enzymes; (2) cirrhosis pattern, which has decreased albumin, elevated gamma globulins (with β–γ bridging on serum electrophoresis) and elevated PT; (3) chronic hepatitis pattern, which has a combination of changes seen in acute hepatitis and cirrhosis patterns; and (4) obstructive liver disease pattern, also called cholestasis, which has an elevated ALP and bilirubin (Table 15-1).

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Table 15-1. Laboratory Studies and Patterns of Liver Disease
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Ascites is often associated with cirrhosis; however, both transudative ascites (seen in patients with cirrhosis, alcoholic hepatitis, or congestive heart failure) and exudative ascites (seen in patients with peritoneal carcinomatosis or tuberculosis) may occur. Differentiating between the two types requires a determination of gradient (i.e., difference between serum albumin and ...

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