T
🔬 How to Read Liver Function Tests (LFTs) at a Clinical Level – Advanced Interpretation
Liver Function Tests (LFTs) help in diagnosing hepatocellular, cholestatic, or synthetic dysfunction. A systematic interpretation based on patterns rather than isolated values is key for clinical accuracy.
🔹 1. Approach to Interpreting LFTs
✅ Step 1: Check the Pattern of Abnormality
- Hepatocellular → High ALT/AST (>5x normal)
- Cholestatic → High ALP & GGT (>3x normal)
- Synthetic Dysfunction → Low Albumin, High PT/INR
✅ Step 2: Evaluate Disease Severity
- Mild (1-2x ULN) → Non-specific / early disease
- Moderate (2-5x ULN) → Moderate damage
- Severe (>10-20x ULN) → Acute or fulminant injury
✅ Step 3: Determine the Etiology
- Acute vs. Chronic: If albumin is low, suggests chronic disease
- AST/ALT Ratio: Helps differentiate alcoholic vs. viral vs. ischemic hepatitis
- Bilirubin Type (Direct vs. Indirect): Helps detect hepatocellular vs. cholestatic causes
✅ Step 4: Look at Additional Tests
- Autoimmune Markers → Autoimmune Hepatitis
- Viral Markers → Hepatitis B & C
- Metabolic Tests → Wilson’s, Hemochromatosis
🔹 2. LFT Interpretation Based on Patterns
A. Hepatocellular Pattern (Liver Cell Injury)
- ALT & AST elevated (>5x normal)
- Bilirubin may be high (if severe)
- ALP & GGT normal/mildly elevated
- Albumin & PT/INR normal (unless severe)
| Possible Causes | Key Findings |
|---|---|
| Viral Hepatitis (A, B, C, E, D) | ALT > AST (↑↑ 500-1000+), Bilirubin ↑ |
| Autoimmune Hepatitis | Very high ALT, Positive ANA, SMA |
| Drug-Induced Liver Injury (DILI) | ALT/AST >1000 if severe |
| Ischemic Liver Injury (Shock Liver) | ALT/AST ↑↑ (>5000 U/L), Low BP history |
| Wilson’s Disease | ALT/AST ↑, Low ALP, High Bilirubin, Neurologic symptoms |
📌 Key Interpretation:
- ALT > AST → Viral, Autoimmune, NAFLD
- AST > ALT (2:1) → Alcoholic Liver Disease
B. Cholestatic Pattern (Biliary Obstruction)
- ALP & GGT elevated (>3x normal)
- Bilirubin high (Direct > Indirect)
- ALT/AST may be normal or mildly high
| Possible Causes | Key Findings |
|---|---|
| Gallstones (Cholelithiasis, Choledocholithiasis) | Sudden ↑ ALP, GGT, Bilirubin |
| Primary Biliary Cholangitis (PBC) | ALP ↑↑, Anti-Mitochondrial Antibody (AMA) |
| Primary Sclerosing Cholangitis (PSC) | ALP ↑↑, Bilirubin ↑, IBD history |
| Pancreatic/Biliary Cancer | Gradual ↑ ALP, GGT, Bilirubin, weight loss |
📌 Key Interpretation:
- If ALP is high & GGT is normal → Bone disease
- If ALP & GGT are both high → Biliary disease
C. Synthetic Dysfunction (Liver Failure)
- Albumin low
- PT/INR prolonged
- Bilirubin high
- AST/ALT may be normal or elevated
| Possible Causes | Key Findings |
|---|---|
| Cirrhosis (Alcoholic, Viral, NAFLD, Autoimmune) | Low albumin, High INR, AST:ALT > 2:1 |
| Acute Liver Failure (Drug-induced, Hepatitis, Wilson’s Disease) | High INR, Bilirubin, Encephalopathy |
📌 Key Interpretation:
- Low Albumin + High INR + High Bilirubin = Advanced Liver Failure
🔹 3. AST/ALT Ratio Interpretation
| Ratio | Condition |
|---|---|
| AST:ALT > 2:1 | Alcoholic Liver Disease |
| AST:ALT > 3:1 | Severe Alcoholic Hepatitis |
| AST:ALT < 1 | Viral Hepatitis, NAFLD |
| AST:ALT > 5:1 | Wilson’s Disease, Muscle Injury |
📌 Example: If AST = 120 and ALT = 40, AST/ALT = 3 → Likely Alcoholic Liver Disease.
🔹 4. Bilirubin Interpretation
| Type | Causes |
|---|---|
| Unconjugated (Indirect) Bilirubin ↑ | Hemolysis, Gilbert’s Syndrome |
| Conjugated (Direct) Bilirubin ↑ | Liver disease, Biliary obstruction |
📌 If direct bilirubin is >50% of total bilirubin, it suggests liver or biliary disease.
🔹 5. Alkaline Phosphatase (ALP) & GGT
| Test | Key Interpretation |
|---|---|
| ALP ↑ + GGT ↑ | Liver/Cholestasis |
| ALP ↑ + GGT Normal | Bone disease |
| ALP Normal + GGT ↑ | Alcoholic liver disease |
📌 Example:
- ALP 350, GGT 400, Bilirubin 3.0 → Cholestasis (Obstruction or PBC)
🔹 6. Interpretation Summary
| LFT Pattern | Likely Causes |
|---|---|
| ALT/AST ↑↑ (ALT > AST) | Hepatitis (Viral, Autoimmune, NAFLD) |
| AST > ALT (2:1 or 3:1 ratio) | Alcoholic Liver Disease |
| ALT/AST > 1000 | Acute Hepatitis, Ischemic Injury, DILI |
| ALP & GGT ↑↑ | Cholestasis, Biliary Disease |
| Bilirubin ↑ with Normal ALP | Hemolysis, Gilbert’s |
| Albumin ↓ + PT/INR ↑ | Cirrhosis, Liver Failure |
🔹 7. Clinical Decision-Making with LFTs
🔹 If ALT > 10x normal?
→ Acute Hepatitis (Viral, Drugs, Ischemia)
🔹 If AST > ALT with High GGT?
→ Alcoholic Liver Disease
🔹 If ALP ↑↑ with Direct Bilirubin?
→ Biliary Obstruction (Gallstones, Cancer)
🔹 If Albumin ↓ & PT/INR ↑?
→ Chronic Liver Disease / Cirrhosis
🔹 8. Case-Based Examples
🔵 Case 1: Viral Hepatitis
- ALT: 1200 U/L
- AST: 850 U/L
- Bilirubin: 2.5 mg/dL
📌 Diagnosis: Acute Hepatitis
🔴 Case 2: Alcoholic Liver Disease
- ALT: 50 U/L
- AST: 130 U/L
- GGT: 220 U/L
📌 Diagnosis: Alcoholic Hepatitis
🟢 Case 3: Biliary Obstruction
- ALP: 450 U/L
- GGT: 500 U/L
- Direct Bilirubin: 4.5 mg/dL
📌 Diagnosis: Choledocholithiasis (Gallstone in Common Bile Duct)