More than 70% of the parenchyma of the liver may be damaged before liver function test results become abnormal. Function is gen-erally measured in terms of serum enzyme activity (ie, alkaline phosphatase, lactic dehydrogenase, serum aminotransferases) and serum concentrations of proteins (albumin and globulins), biliru-bin, ammonia, clotting factors, and lipids. Several of these tests may be helpful for assessing patients with liver disease. However, the na-ture and extent of hepatic dysfunction cannot be determined by these tests alone, as many other disorders can affect their results.
Serum aminotransferases (also called transaminases) are sensi-tive indicators of injury to the liver cells and are useful in detect-ing acute liver disease such as hepatitis. Alanine aminotransferase (ALT) (formerly called serum glutamic-pyruvic transaminase [SGPT]), aspartate aminotransferase (AST) (formerly called serum glutamic-oxaloacetic transaminase [SGOT]), and gamma glu-tamyl transferase (GGT) (also called G-glutamyl transpeptidase) are the most frequently used tests of liver damage. ALT levels in-crease primarily in liver disorders and may be used to monitor the course of hepatitis or cirrhosis or the effects of treatments that may be toxic to the liver. AST is present in tissues that have high metabolic activity; thus, the level may be increased if there is damage to or death of tissues of organs such as the heart, liver, skeletal muscle, and kidney. Although not specific to liver disease, levels of AST may be increased in cirrhosis, hepatitis, and liver cancer. Increased GGT levels are associated with cholestasis but can also be due to alcoholic liver disease. Although the kidney has the highest level of the enzyme, the liver is considered the source of normal serum activity. The test determines liver cell dysfunc-tion and is a sensitive indicator of cholestasis. Its main value in liver disease is confirming the hepatic origin of an elevated alka-line phosphatase level. Common liver function tests are listed in Table 39-1.
Liver biopsy is the removal of a small amount of liver tissue, usu-ally through needle aspiration. It permits examination of liver cells. The most common indication is to evaluate diffuse disorders of the parenchyma and to diagnose space-occupying lesions. Liver biopsy is especially useful when clinical findings and laboratory tests are not diagnostic. Bleeding and bile peritonitis after liver biopsy are the major complications; therefore, coagulation studies are obtained, their values are noted, and abnormal results are treated before liver biopsy is performed. Other techniques for liver biopsy are preferred if ascites or coagulation abnormalities exist. A liver biopsy can be performed percutaneously under ultrasound guid-ance or transvenously through the right internal jugular vein to right hepatic vein under fluoroscopic control. Liver biopsy can also be performed laparoscopically. Nursing responsibilities re-lated to percutaneous liver biopsy are summarized in Chart 39-1
Ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) are used to identify normal structures and abnormalities of the liver and biliary tree. A radioisotope liver scan may be performed to assess liver size and hepatic blood flow and obstruction.
Laparoscopy (insertion of a fiber-optic endoscope through a small abdominal incision) is used to examine the liver and other pelvic structures. It is also used to perform guided liver biopsy, to determine the etiology of ascites, and to diagnose and stage tumors of the liver and other abdominal organs.
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