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Liver Function Test (LFT) Interpretation - Simple Guide
LFTs are a panel of blood tests that assess different aspects of liver health. The key is to look at the pattern, not just individual values.
The Tests and What They Measure
| Test | What It Tells You |
|---|---|
| ALT (Alanine aminotransferase) | Liver cell damage - more liver-specific |
| AST (Aspartate aminotransferase) | Liver cell damage - less specific (also in muscle, heart) |
| ALP (Alkaline phosphatase) | Bile duct / cholestasis |
| GGT (Gamma-glutamyl transferase) | Bile duct injury; also elevated with alcohol |
| Bilirubin (total/direct) | Jaundice, bile flow obstruction, hemolysis |
| Albumin | Liver's ability to make protein (synthetic function) |
| PT / INR | Clotting factors made by liver (synthetic function) |
The 3 Key Patterns
1. Hepatocellular Pattern (liver cell damage)
- ALT and AST predominantly elevated
- Suggests: viral hepatitis, alcohol, toxins/drugs, ischemia, fatty liver
- Clue: ALT > AST typically suggests non-alcoholic causes; AST:ALT > 2:1 suggests alcoholic liver disease
- Fulminant failure: AST/ALT can exceed 10,000 IU/L
2. Cholestatic Pattern (bile flow problem)
- ALP and GGT predominantly elevated
- Bilirubin elevated
- Suggests: bile duct obstruction (gallstones, cancer), primary biliary cholangitis, drug-induced cholestasis, intrahepatic cholestasis
3. Synthetic Dysfunction (liver is failing)
- Low albumin + high PT/INR
- Indicates the liver can no longer produce key proteins
- Seen in cirrhosis, acute liver failure
- Often accompanied by low platelets, electrolyte abnormalities, and raised ammonia (causing encephalopathy)
Quick Summary Table
| Pattern | Main Abnormality | Think of... |
|---|---|---|
| Hepatitis | ↑↑ ALT, AST | Viral hepatitis, drugs, alcohol |
| Cholestasis | ↑↑ ALP, GGT + bilirubin | Bile duct block, PBC |
| Liver failure | ↓ Albumin, ↑ INR | Cirrhosis, acute liver failure |
| Mixed | All elevated | Severe/advanced disease |
Practical Tips
- Always interpret LFTs as a pattern, not in isolation
- Isolated bilirubin elevation with normal other tests - think hemolysis or Gilbert syndrome
- ALP elevation without GGT - could be bone disease, not liver
- Mildly raised AST alone - could be muscle (check CK), heart, or thyroid
- Low albumin is a late sign - the liver has large reserve capacity
(Based on: Tietz Textbook of Laboratory Medicine, 7th Ed. and Henry's Clinical Diagnosis and Management by Laboratory Methods)
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