Markers of hepatic damage

• Alanine aminotransferase (ALT)

• Aspartate aminotransferase (AST)

• Lactate dehydrogenase (LDH)

Patterns and ratios of various enzymes are variable and unreliable diagnostic indicators. Measurement of ALT alone is usually sufficient. It is more liver-specific but less sensitive than AST and has a longer half-life.

AST is not liver-specific but is a sensitive indicator of hepatic damage. The plasma level is proportional to the degree of hepatocellular damage. Low levels occur in extrahepatic obstruction and inactive cirrhosis.

LDH is insensitive and non-specific. Isoenzyme electrophoresis is needed to distinguish cardiac, erythrocyte, skeletal muscle and liver injury.

Acute phase reactants such as C-reactive protein (CRP) are also produced by the liver. Levels increase during critical illness and following hepatocellular injury.

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