What is the kinetics of Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) change duration?

From the Guidelines

The kinetics of AST and ALT changes following liver injury, such as HBV reactivation, typically show elevation within a few weeks or days of the rise in HBV DNA levels, with peak levels occurring as the patient develops HBV-reactivation related hepatitis.

Key Points

• The natural history of HBV reactivation may be classified into several stages, including increased viral replication, increase in serum ALT and AST, spontaneous or on-treatment improvement/resolution, acute liver failure/persistent liver injury, and resolution with immune recovery 1.
• Approximately within a few weeks (or in some cases days) of a rise in HBV DNA levels, serum alanine and aspartate aminotransferases start rising, with levels typically increasing 5-10 times the upper limit of normal (ULN) or baseline levels 1.
• The majority of patients may remain asymptomatic, but a small number of patients experiencing a more severe flare of hepatitis may experience constitutional symptoms, right upper quadrant tenderness, and jaundice 1.
• The duration of elevation depends on the underlying cause, the severity of injury, and whether the injurious agent persists, with complete normalization of transaminases indicating resolution of acute injury but not necessarily reflecting full recovery of liver function 1.

AST and ALT Elevation

• AST tends to rise more rapidly than ALT initially, but ALT often remains elevated longer due to its longer half-life 1.
• In acute hepatocellular injury, these enzymes can increase to levels 10-20 times the upper limit of normal, with resolution typically occurring over 1-2 weeks if the injurious agent is removed 1.
• However, in cases of ongoing liver damage such as alcoholic hepatitis or chronic viral hepatitis, elevations may persist for months 1.

Diagnostic Clues

• The AST:ALT ratio can provide diagnostic clues, with ratios >2 suggesting alcoholic liver disease, while ratios <1 are more typical of viral hepatitis or nonalcoholic fatty liver disease 1.
• Levels of AST more than 500 IU/L or an ALT 200 IU/L are uncommonly seen with alcoholic hepatitis and should suggest another etiology 1.

From the Research

Kinetics of Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) Change

The kinetics of AST and ALT change can be described as follows:

• AST and ALT levels rise rapidly after acute acetaminophen overdose, with a doubling time of 9.5 hours 2
• AST and ALT levels are closely aligned, with a 1:1 ratio, but fall at different rates, with AST falling faster than ALT 3
• The half-life of AST is 15.1 hours, while the half-life of ALT is 39.6 hours 3
• AST returns to baseline more quickly than ALT, with a potential benefit of using AST for discontinuing acetylcysteine treatment 3

Change Duration

The change duration of AST and ALT can be described as follows:

• AST and ALT levels can rise to peak levels within 24-48 hours after acetaminophen overdose 2, 3
• AST levels can fall to below 50% of peak levels within 24 hours, while ALT levels take longer to fall 3
• The optimal cut-off values for AST and ALT in diagnosing blunt liver injury are 109 U/l and 97 U/l, respectively, with a sensitivity and specificity of 81% and 82% for AST, and 78% and 88% for ALT 4

Key Findings

• AST and ALT levels are useful biomarkers for liver damage, but have different kinetics and half-lives 5, 6, 2, 3
• The ratio of AST to ALT can be used to differentiate between alcoholic and non-alcoholic liver disease, with a ratio greater than 2 indicating alcoholic liver disease 6
• AST and ALT levels can be used to predict the risk of hepatotoxicity and coagulopathy after acetaminophen overdose 2, 3