"Liver function tests" mainly measure damage, not function. The tests that reflect the synthetic function of the liver are the prothrombin time (INR), the albumin and the bilirubin — and they become abnormal late. A cirrhotic liver can have entirely normal transaminases.
Reference ranges
Interpreting the pattern
| Pattern | Predominant | Consider |
|---|---|---|
| Hepatocellular | ALT and AST ↑↑, ALP normal | Viral hepatitis, drugs, alcohol, autoimmune hepatitis, ischaemic hepatitis, steatohepatitis |
| Cholestatic | ALP and GGT ↑↑, bilirubin ↑ | Gallstones, stricture, tumour, primary biliary cholangitis, drugs |
| Mixed | Both raised | Drug-induced liver injury is the commonest cause |
| Isolated bilirubin | Unconjugated, the others normal | Gilbert's syndrome, haemolysis |
The R value = (ALT / upper limit of normal) / (ALP / upper limit of normal). An R > 5 indicates hepatocellular injury, R < 2 cholestatic injury, and 2–5 a mixed pattern.
Orders of magnitude that direct the work-up
- ALT > 50 × the upper limit of normal: paracetamol poisoning, ischaemic hepatitis ("shock liver") or acute viral hepatitis. The three are distinguished by the history and the speed of the course.
- An AST/ALT ratio > 2 with moderately raised values suggests alcohol-related liver disease; a ratio < 1 suggests steatohepatitis or viral hepatitis.
- An isolated raised ALP — check the GGT. A normal GGT shifts the suspicion to bone, pregnancy or malignancy.
- A markedly raised GGT with the other tests normal is most often enzyme induction by alcohol or drugs and is often of no clinical significance.
Synthetic function and prognosis
Child–Pugh
| Parameter | 1 point | 2 points | 3 points |
|---|---|---|---|
| Bilirubin (µmol/L) | < 34 | 34–50 | > 50 |
| Albumin (g/L) | > 35 | 28–35 | < 28 |
| INR | < 1.7 | 1.7–2.3 | > 2.3 |
| Ascites | None | Mild | Moderate–severe |
| Encephalopathy | None | Grade 1–2 | Grade 3–4 |
Class A = 5–6 points, B = 7–9, C = 10–15. MELD-Na is used for transplant prioritisation; both are available among the calculators.
Fibrosis markers
| Index | Calculation | Interpretation |
|---|---|---|
| FIB-4 | (age × AST) / (platelets × √ALT) | < 1.3 excludes advanced fibrosis; > 2.67 strongly suggests it |
| APRI | (AST/upper limit) / platelets × 100 | > 1.0 suggests fibrosis |
| Elastography | kPa | > 15 kPa suggests advanced fibrosis |
Work-up of unexplained raised liver tests
Repeat the tests first — a transient rise is common. If the abnormality persists: hepatitis serology (A, B, C, E), iron studies and ferritin, ANA, SMA, AMA, IgG subclasses, caeruloplasmin in people under 40, alpha-1 antitrypsin, TSH and coeliac serology, together with ultrasound of the liver and biliary tract. Go through the medication and any herbal preparations carefully — drug-induced liver injury is the commonest cause of acute liver failure in the Nordic countries.
