AST to ALT Ratio in Ischemic Hepatitis
In ischemic hepatitis, the AST to ALT ratio is typically less than 1.5, with both enzymes markedly elevated (often >1000 IU/L), but the key distinguishing feature is a dramatically elevated lactate dehydrogenase (LDH) with an ALT/LDH ratio of approximately 0.87.
Characteristic Enzyme Pattern
The enzyme pattern in ischemic hepatitis differs significantly from other causes of acute hepatocellular injury:
AST and ALT elevations: Both are severely elevated (typically >1000 IU/L), representing acute hepatocyte necrosis from hypoperfusion 1, 2, 3
AST/ALT ratio: Generally **<1.5** in ischemic hepatitis, which helps differentiate it from alcoholic hepatitis (where AST/ALT is typically >2) 1
The LDH is the critical discriminator: Ischemic hepatitis causes disproportionately elevated LDH compared to viral hepatitis or other causes 4
The ALT/LDH Ratio: Most Useful Diagnostic Tool
The ALT/LDH ratio is more diagnostically valuable than the AST/ALT ratio for ischemic hepatitis:
- Ischemic hepatitis: ALT/LDH ratio = 0.87 (mean value)
- Viral hepatitis: ALT/LDH ratio = 4.65 (mean value)
- Acetaminophen toxicity: ALT/LDH ratio = 1.46 (mean value)
An ALT/LDH ratio of <1.5 has 94% sensitivity and 84% specificity for distinguishing ischemic hepatitis from viral hepatitis 4. This makes the LDH measurement essential when evaluating patients with severe transaminase elevations.
Clinical Context
Ischemic hepatitis occurs in the setting of:
- Severe heart failure with reduced cardiac output
- Circulatory shock (cardiogenic, septic, or hypovolemic)
- Severe hypotension with inadequate hepatic perfusion 5, 6
The diagnosis requires correlation with hemodynamic parameters (blood pressure, cardiac output, central venous pressure) alongside the enzyme pattern 5.
Common Pitfall
Do not rely solely on AST/ALT ratio to diagnose ischemic hepatitis. While it's typically <1.5, this overlaps with many other conditions. Always order LDH when evaluating severe transaminase elevations (>1000 IU/L), as the markedly elevated LDH with low ALT/LDH ratio is the pathognomonic feature of ischemic hepatitis 4.
The prognosis of ischemic hepatitis is generally poor, reflecting the severity of the underlying hemodynamic compromise 3.