How to classify abnormal liver function tests by pattern, narrowing the differential before ordering more tests.
Step 1: Identify the Pattern
| Pattern | Key markers |
|---|
| Hepatocellular | ALT and AST predominate |
| Cholestatic | ALP and GGT predominate, often with bilirubin |
| Mixed | Both patterns present together |
Step 2: Consider the Magnitude
- Mild elevation (<5x normal): common — fatty liver, alcohol, medications, chronic viral hepatitis
- Marked elevation (>15x normal): think ischemic hepatitis (shock liver), toxin/drug-induced (e.g. acetaminophen overdose), or acute viral hepatitis
Common Causes by Pattern
| Hepatocellular | Cholestatic |
|---|
| Viral hepatitis (A, B, C) | Bile duct obstruction (stones, stricture, tumor) |
| Alcohol-related liver disease | Primary biliary cholangitis |
| Non-alcoholic fatty liver disease | Drug-induced cholestasis |
| Drug-induced (e.g. acetaminophen) | Infiltrative disease |
| Autoimmune hepatitis | Primary sclerosing cholangitis |
Initial Workup
Viral hepatitis serologies, abdominal ultrasound (especially for a cholestatic pattern, to look for ductal dilation), a thorough medication and alcohol history, and INR/albumin to assess synthetic liver function. If cirrhosis is established, see the Child-Pugh and MELD-Na calculators for severity grading.
Frequently Asked Questions
Does ALT or AST being higher matter?
An AST:ALT ratio above 2 is classically associated with alcohol-related liver disease, though this isn't absolute and should be interpreted alongside the clinical picture.
Is ultrasound always needed?
It's especially useful when the pattern is cholestatic, to look for bile duct dilation suggesting an obstructive cause that might need an intervention.
Can LFTs be normal in significant liver disease?
Yes — advanced cirrhosis can have relatively normal transaminases despite significant underlying damage, since there's less functioning liver tissue left to release enzymes from.