11-27-2008, 10:46 AM
Aminotransferases [alanine aminotransferase (ALT) and aspartate aminotransferase (AST)]
ALT is more sensitive and specific than AST for liver damage.
ALT and AST usually have a similar increase. The exception is in alcoholic hepatitis, in which the AST“ALT ratio may be >2:1.
If ALT and AST levels are mildly elevated (low hundreds), think of chronic viral hepatitis or acute alcoholic hepatitis.
If ALT and AST levels are moderately elevated (high hundreds to thousands), think of acute viral hepatitis.
If ALT and AST levels are severely elevated (>10,000), extensive hepatic necrosis has occurred. Typical cases are:
Ischemia, shock liver (prolonged hypotension or circulatory collapse)
Acetaminophen toxicity
Severe viral hepatitis
Note that liver transaminases are often normal or even low in patients with cirrhosis (without any active cell necrosis) or metastatic liver disease, because the number of healthy functioning hepatocytes is markedly reduced.
The following can cause an elevation in ALT or AST levels in asymptomatic patients (note the mnemonic):
Autoimmune hepatitis
Hepatitis B
Hepatitis C
Drugs or toxins
Ethanol
Fatty liver (triglyceridemia)
Growths (tumors)
Hemodynamic disorders (e.g., CHF)
Iron (hemochromatosis), copper (Wilson's disease), or AAT deficiency
ALT is primarily found in the liver.
AST is found in many tissues (e.g., skeletal muscle, heart, kidney, brain).
In alcoholic hepatitis, the AST level is almost never >500, and the ALT level is almost never >300.
The higher the AST“ALT ratio, the greater the likelihood that alcohol is contributing to the abnormal LFTs.
LFT pearls
Cholestatic LFTs: markedly elevated alkaline phosphatase and GGT; ALT and AST slightly elevated
Hepatocellular necrosis or inflammation: normal or slightly elevated alkaline phosphatase; markedly elevated ALT and AST
Alkaline phosphatase (ALK-P): Not specific to liver”also found in bone, gut, and placenta
ALK-P is elevated when there is obstruction to bile flow (e.g., cholestasis) in any part of the biliary tree. Normal levels make cholestasis unlikely.
If levels are very high (10-fold increase), think of extrahepatic biliary tract obstruction or intrahepatic cholestasis (e.g., PBC or drug-induced cirrhosis).
If levels are elevated, measure the GGT (Gamma-glutamyl-transferase) level to make sure the elevation is hepatic in origin (rather than bone or intestinal). If the GGT level is also elevated, this strongly suggests a hepatic origin. If the GGT level is normal but ALK-P is elevated, consider pregnancy or bone disease.
Bilirubin (will post seperate)
GGT is often used to confirm that the ALK-P elevation is of hepatic origin.
Albumin decreased in chronic liver disease, nephrotic syndrome, malnutrition, and inflammatory states (e.g., burns, sepsis, trauma)
Prothrombin time (PT)
The liver synthesizes clotting factors I, II, V, VII, IX, X, XII, and XIII, the function of which is reflected by PT.
PT is not prolonged until most of the liver's synthetic capacity is lost, which corresponds to advanced liver disease.
Cholestasis refers to obstruction of bile flow from any cause. If LFTs reveal cholestasis, obtain an abdominal or RUQ ultrasound.
ALT is more sensitive and specific than AST for liver damage.
ALT and AST usually have a similar increase. The exception is in alcoholic hepatitis, in which the AST“ALT ratio may be >2:1.
If ALT and AST levels are mildly elevated (low hundreds), think of chronic viral hepatitis or acute alcoholic hepatitis.
If ALT and AST levels are moderately elevated (high hundreds to thousands), think of acute viral hepatitis.
If ALT and AST levels are severely elevated (>10,000), extensive hepatic necrosis has occurred. Typical cases are:
Ischemia, shock liver (prolonged hypotension or circulatory collapse)
Acetaminophen toxicity
Severe viral hepatitis
Note that liver transaminases are often normal or even low in patients with cirrhosis (without any active cell necrosis) or metastatic liver disease, because the number of healthy functioning hepatocytes is markedly reduced.
The following can cause an elevation in ALT or AST levels in asymptomatic patients (note the mnemonic):
Autoimmune hepatitis
Hepatitis B
Hepatitis C
Drugs or toxins
Ethanol
Fatty liver (triglyceridemia)
Growths (tumors)
Hemodynamic disorders (e.g., CHF)
Iron (hemochromatosis), copper (Wilson's disease), or AAT deficiency
ALT is primarily found in the liver.
AST is found in many tissues (e.g., skeletal muscle, heart, kidney, brain).
In alcoholic hepatitis, the AST level is almost never >500, and the ALT level is almost never >300.
The higher the AST“ALT ratio, the greater the likelihood that alcohol is contributing to the abnormal LFTs.
LFT pearls
Cholestatic LFTs: markedly elevated alkaline phosphatase and GGT; ALT and AST slightly elevated
Hepatocellular necrosis or inflammation: normal or slightly elevated alkaline phosphatase; markedly elevated ALT and AST
Alkaline phosphatase (ALK-P): Not specific to liver”also found in bone, gut, and placenta
ALK-P is elevated when there is obstruction to bile flow (e.g., cholestasis) in any part of the biliary tree. Normal levels make cholestasis unlikely.
If levels are very high (10-fold increase), think of extrahepatic biliary tract obstruction or intrahepatic cholestasis (e.g., PBC or drug-induced cirrhosis).
If levels are elevated, measure the GGT (Gamma-glutamyl-transferase) level to make sure the elevation is hepatic in origin (rather than bone or intestinal). If the GGT level is also elevated, this strongly suggests a hepatic origin. If the GGT level is normal but ALK-P is elevated, consider pregnancy or bone disease.
Bilirubin (will post seperate)
GGT is often used to confirm that the ALK-P elevation is of hepatic origin.
Albumin decreased in chronic liver disease, nephrotic syndrome, malnutrition, and inflammatory states (e.g., burns, sepsis, trauma)
Prothrombin time (PT)
The liver synthesizes clotting factors I, II, V, VII, IX, X, XII, and XIII, the function of which is reflected by PT.
PT is not prolonged until most of the liver's synthetic capacity is lost, which corresponds to advanced liver disease.
Cholestasis refers to obstruction of bile flow from any cause. If LFTs reveal cholestasis, obtain an abdominal or RUQ ultrasound.
