Enzymes
AST (aspartate aminotransferase): 10-40 IU/L. ALT (alanine aminotransferase): 7-56 IU/L. Both released with hepatocellular injury. AST:ALT ratio >2:1: alcoholic liver disease. AST:ALT ratio <1: non-alcoholic fatty liver, viral hepatitis. Alkaline phosphatase (ALP): 44-147 IU/L. Elevated: cholestasis (biliary obstruction), bone disease, pregnancy. GGT (gamma-glutamyl transferase): 0-30 IU/L. Elevated with alcohol use, biliary disease (confirms ALP is hepatic). LDH: elevated in liver injury.
Bilirubin and Proteins
Total bilirubin: 0.3-1.2 mg/dL. Direct (conjugated): 0.0-0.3. Indirect (unconjugated): total minus direct. Direct elevated: biliary obstruction, Dubin-Johnson. Indirect elevated: hemolysis, Gilbert syndrome, neonatal jaundice. Total protein: 6.0-8.3 g/dL. Albumin: 3.5-5.0 g/dL (synthesized by liver — low with cirrhosis, malnutrition, nephrotic syndrome). Globulin: 2.0-3.5 g/dL (elevated in chronic inflammation, multiple myeloma). A:G ratio: 1.2-2.0.
Patterns
Hepatocellular: AST/ALT elevated (more than ALP/bilirubin) — viral hepatitis, alcoholic hepatitis, NAFLD, drug-induced. Cholestatic: ALP and bilirubin elevated (more than AST/ALT) — biliary obstruction, primary biliary cholangitis, primary sclerosing cholangitis. Mixed: both patterns. Isolated hyperbilirubinemia: hemolysis, Gilbert, medications. Very high ALT (>1000): viral hepatitis, ischemic liver, drug-induced (acetaminophen). Low albumin: cirrhosis, malnutrition, nephrotic, burns, inflammation. PT elevated (clotting factors): severe liver disease.
Important Notes
- AST:ALT ratio >2:1 is classic for alcoholic liver disease; ratio <1 is typical for non-alcoholic fatty liver disease and viral hepatitis.
- Very high ALT (>1000 IU/L) suggests viral hepatitis, ischemic liver injury (shock liver), or drug-induced liver injury (acetaminophen).
Clinical Tips
- GGT confirms that elevated ALP is from liver (not bone) — both elevated together suggests hepatic source.
- Elevated direct (conjugated) bilirubin suggests biliary obstruction; elevated indirect (unconjugated) suggests hemolysis or Gilbert syndrome.
Summary
Liver function test interpretation requires recognizing hepatocellular (AST/ALT) vs cholestatic (ALP/bilirubin) patterns and understanding protein synthesis (albumin, clotting factors).
