Tests in Liver Disease: Usefulness and Interpretation

⚠️ These are not true “liver function tests” but rather markers of liver damage or cholestasis. 👉 Normal LFTs ≠ normal liver. 🚨 The three main causes of severe derangement of all enzymes are: Hepatic ischaemia, Viral hepatitis, and Drugs/Toxins.

🧪 Key Liver Blood Tests

• 🔴 AST (Aspartate Aminotransferase) – Raised in liver injury (esp. alcohol-related) but not liver-specific. Also elevated in heart and muscle disease.
• 🟠 ALT (Alanine Aminotransferase) – More specific to hepatocyte injury (e.g. viral hepatitis, NAFLD).
• 🟡 ALP (Alkaline Phosphatase) – Marker of cholestasis or obstruction. Also made in bone & placenta ➡️ check GGT to confirm hepatic origin.
• 🟢 GGT (Gamma-Glutamyl Transferase) – Rises with ALP in biliary disease. Sensitive to alcohol and drugs (phenytoin, barbiturates).
• 💛 Bilirubin – Breakdown product of haem. – Conjugated ↑ → obstruction, hepatocellular disease – Unconjugated ↑ → haemolysis, Gilbert’s syndrome.
• 💙 Albumin – Low in chronic liver disease (ascites, oedema). Also reduced in nephrotic syndrome, sepsis, malnutrition.
• 🩸 PT/INR – Prolonged if liver fails to make clotting factors. Important in paracetamol overdose & acute liver failure. Always give Vit K to exclude deficiency.
• 🟣 Platelets – Low in cirrhosis due to splenomegaly & portal hypertension.
• 🧬 AFP (Alpha-Fetoprotein) – Tumour marker for hepatocellular carcinoma (HCC).
• ☁️ Ammonia – Raised in hepatic encephalopathy (toxic accumulation).
• 🔍 Liver Biopsy – Gold standard for diagnosis & staging fibrosis (can be via jugular if coagulopathy).
• 📡 FibroScan – Non-invasive measure of stiffness (fibrosis/cirrhosis).
• 🖼️ Imaging (USS, CT, MRI) – Liver size, morphology, masses, biliary tree, ascites, vascular flow.

📖 Focused History for Abnormal LFTs

• 💊 Medications – recent antibiotics, herbal remedies, paracetamol use.
• 🌍 Travel – rural/countryside, water sports (e.g. leptospirosis).
• 💉 IV or recreational drug use (Hep B/C risk).
• 🍺 Alcohol intake – CAGE questions, history of withdrawal (DTs).
• ❤️ Sexual history & transfusions pre-1990 (HIV, Hepatitis risk).
• 🤒 Associated symptoms – fever, rigors, vomiting, pale stools, dark urine, pruritus, weight loss, abdo pain.
• 🔎 Features of chronic liver disease – ascites, encephalopathy, coagulopathy, jaundice.

🚨 Causes of Liver Injury

• 🦠 Viral hepatitis (A–E, CMV, EBV, HSV).
• 🍺 Alcohol-related liver disease.
• 💊 Drug-induced hepatotoxicity (paracetamol, statins, anti-TB meds).
• 💔 Ischaemic hepatitis (“shock liver”).
• 🟢 Obstructive jaundice (stones, tumours, PSC/PBC).
• ⚖️ NAFLD with T2DM (AST > ALT pattern).

🧾 Interpretation of Specific Tests

• 🩸 PT/INR – Reflects liver synthetic function. Raised in paracetamol OD, fulminant failure. Always try Vit K → persistent abnormality = true liver dysfunction.
• 💙 Albumin – Falls in cirrhosis, but also sepsis, nephrotic syndrome, malnutrition.
• 💧 Urea – Often low in liver disease (reduced metabolism). High in GI bleed (protein load).
• ☁️ Ammonia – Linked to encephalopathy, esp. fulminant liver failure.
• 🟡 Bilirubin – Conjugated ↑ = obstruction; Unconjugated ↑ = haemolysis, Gilbert’s.
• 🟡 ALP – Canalicular enzyme, cholestasis. Cross-check with GGT.
• 🟠 AST/ALT – – AST:ALT > 2 → Alcoholic liver disease 🍺 – ALT more specific to liver 🧡 – Mild ↑ (<100): chronic hepatitis, fatty liver – Moderate ↑ (100–300): autoimmune hepatitis, NASH, Wilson’s – Marked ↑ (>300): paracetamol OD, viral hepatitis, ischaemia.

🧪 Further Investigations (“Liver Screen”)

• 🦠 Viral serology – HBsAg, HCV Ab, HAV IgM, HSV, CMV, HIV, ± Hepatitis D IgM.
• 🧬 Autoimmune markers – ANA, ASMA, AMA, immunoglobulins.
• ⚖️ Metabolic – Ferritin, transferrin saturation, caeruloplasmin & copper (if <55), A1AT phenotype.
• 🩸 AFP – screen for HCC.
• 🩺 Imaging – USS (structure, obstruction, PV patency), MRCP/ERCP if obstructive pattern.
• 💉 Biopsy – histology & fibrosis staging.
• 🚨 NAC early if any suspicion of paracetamol overdose.