They mostly ordered in case of acute hepatoceulllar injury (e.g. viral or drug); precedes increase in serum bilirubin by approximately 1 week.
- Hepatocellular damage, liver cell necrosis, or injury of any cause.
- Alcoholic hepatitis (AST > ALT).
- Viral and chronic hepatitis (ALT > AST).
- Early acute hepatitis: AST is usually higher initially, but by 48 hours, ALT is usually higher.
- AST levels of 500 U/L suggest acute hepatocellular injury; seldom >500 U/L in obstructive jaundice, cirrhosis, viral hepatitis, AIDS, alcoholic liver disease.
- Acute fulminant viral hepatitis: Abrupt AST rise may be seen (rarely >4,000 IU/L) and declines more slowly; positive serologic tests and acute chemical injury.
- Congestive heart failure, arrhythmia, sepsis, and gastrointestinal tract hemorrhage:- AST levels reach a peak of 1,000–9,000 U/L, declining by 50% within 3 days and to <100 U/L within a week, suggesting shock liver with centrolobular necrosis. Serum bilirubin and ALP reflect underlying disease.
- Trauma to skeletal or heart muscle.
- Acute heart failure (AST > ALT).
- Severe exercise, burns, heat stroke.
- Drug-induced injury to the liver.
- Acute bile duct obstruction due to a stone: Rapid rise of AST and ALT to very high levels (e.g., >600 U/L and often >2,000 U/L) followed by a sharp fall in 12–72 hours is said to be typical.
- Chronic renal dialysis
- Pyridoxal phosphate deficiency states (e.g., malnutrition, pregnancy, alcoholic liver disease)
- Half-life of AST is 18 hours and that of ALT is 48 hours.
- The patient is rarely asymptomatic with ALT and AST levels >1,000 U/L.
- AST >10 times normal indicates acute hepatocellular injury, but lesser increases are nonspecific and may occur with virtually any form of liver injury.
- Increases ≤8 times upper limit of normal are nonspecific; may be found in any liver disorder.
- Rarely increased >500 U/L (usually <200 U/L) in posthepatic jaundice (i.e. obstructive jaundice), AIDS, cirrhosis, and viral hepatitis.
- Usually <50 U/L in fatty liver.
- Less than 100 U/L in alcoholic cirrhosis; ALT is normal in 50%, and AST is normal in 25% of these cases.
- Less than 150 U/L in alcoholic hepatitis (may be higher if the patient has delirium tremens).
- Less than 200 U/L in approximately 50% of patients with cirrhosis, metastatic liver disease, lymphoma, and leukemia.
- Degree of increment has a poor prognostic value.
- Persistent increase may indicate chronic hepatitis.
- Mild increase of AST and ALT (usually <500 U/L) with ALP increased greater than three times normal indicates cholestatic jaundice, but more marked increase of AST and ALT (especially >1,000 U/L) with ALP increased less than three times normal indicates hepatocellular jaundice.
- Rapid decline in AST and ALT is a sign of recovery from disease but in acute fulminant hepatitis may represent loss of hepatocytes and poor prognosis.
- Poor correlation of increased concentration with extent of liver cell necrosis and has a little prognostic value.
- Although AST, ALT, and bilirubin are most characteristic of acute hepatitis, they are unreliable markers of severity of injury.
- ALT has 45% variation during the day; highest in afternoon and lowest at night. Both AST and ALT exhibit 10–30% variation from 1 day to next. AST levels are 15% higher in African American men.
- Sankara Nethralaya’s Manual of Medical Laboratory Techniques
- Wallach’s Interpretation of Diagnostic Tests Pathways to Arriving at a Clinical Diagnosis