Which Liver Function Tests Indicate Liver Failure
Liver failure is indicated by impaired hepatic synthetic function, specifically prolonged prothrombin time/INR, decreased serum albumin, and elevated bilirubin—not by elevated aminotransferases (ALT/AST) alone. 1
Critical Distinction: Liver Injury vs. Liver Failure
The term "liver function tests" is misleading because most commonly ordered tests (ALT, AST, ALP, GGT) actually measure hepatocellular injury or cholestasis, not liver function. 2, 3
Tests that truly assess liver function and indicate failure:
- Prothrombin time/INR: Prolonged INR reflects impaired synthesis of clotting factors and indicates compromised synthetic capacity 1, 3
- Serum albumin: Decreased levels (<3.5 g/dL) suggest chronic synthetic dysfunction 1, 3
- Serum bilirubin: Elevated bilirubin is considered the best single test of overall liver function 3
Why Aminotransferases Don't Indicate Liver Failure
High ALT and AST levels do not automatically indicate liver failure. 4 These enzymes simply reflect hepatocyte injury and necrosis, not the liver's ability to perform its synthetic and metabolic functions. 1, 2
Critical Pitfall to Avoid
Normal LFTs do not exclude liver failure or cirrhosis. 1, 4 Patients can have advanced liver disease, significant fibrosis, or even cirrhosis with persistently normal aminotransferases. 1, 5 The degree of LFT elevation does not correlate with disease severity or prognosis. 5
Comprehensive Assessment of Liver Failure
When evaluating for liver failure, the initial laboratory panel should include: 1
- Bilirubin (total and direct)
- INR/prothrombin time
- Albumin
- Platelet count (thrombocytopenia suggests advanced disease)
- AST and ALT (for injury pattern, not function)
- Alkaline phosphatase (for cholestatic component)
Severity Classification Systems
Child-Pugh Classification incorporates the key functional parameters: 1
- Albumin level
- Bilirubin level
- Prothrombin time/INR
- Plus clinical assessments (encephalopathy, ascites)
MELD Score uses: 1
- Bilirubin
- Creatinine
- INR
These scoring systems are used for transplant allocation and prognosis because they measure actual liver function, not just injury. 1
Clinical Context Matters
In acute heart failure, liver function tests are often impaired due to hemodynamic derangements (reduced cardiac output and venous congestion), and abnormal results identify patients at risk of poor prognosis. 6 This demonstrates that LFT abnormalities must be interpreted in clinical context—they may reflect hepatic congestion rather than intrinsic liver failure.