Understanding Liver Function Tests: Albumin, AST, ALT, ALP, GGT, Bilirubin, and Prothrombi, Lecture notes of Physiology

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Data Interpretation: LFTs

Kritica Dwivedi

Liver Function Tests

• Albumin
• AST (aspartate transferase)
• ALT (alanine transferase)
• ALP (alkaline phosphatase)
• GGT (gamma glutamyltransferase)
• Bilirubin
• Prothrombin time/INR

Liver Function Tests

Albumin - Synthetic function

• Chronic assessment (half-life 20 days) AST - Hepatocyte damage ALT - Hepatocyte damage
• More sensitive than AST ALP - Increased in cholestatic disease GGT - Produced in bile tract
• Induced by alcohol Bilirubin - Red cell breakdown
• increased red cell breakdown or decreased biliary excretion Prothrombin time/INR - Vit K dependent clotting factors

Sources - extrahepatic

Test Extra-hepatic source Bilirubin AST ALT ALP

Bilirubin

Bilirubin

• Unconjugated
  • Present in blood
  • Not soluble in water
• Conjugated
  • Conjugated in liver
  • Excreted via bile into small intestine
  • Converted to urobilinogen (excreted in urine) and stercobilin (excreted in faeces)

Jaundice

• Yellowing - caused by bilirubin
• Pre-hepatic
• Hepatic
• Post-hepatic

Jaundice - causes

• Pre-hepatic
  • Haemolysis
  • Ineffective red cell production (Vit B12 deficiency)
• Hepatic
  • Hepatitis
  • Cirrhosis
  • Tumours
  • Drugs
  • Gilbert’s
    • Post-hepatic
      • Gallstones
      • Biliary stricture
      • Ca – cholangiocarcinoma, head of pancrease
      • Cholangitis

Hepatitis – Chronic/Cirrhosis

• ↑ ALT / AST
• Other LFTs may be normal
• Could be ↓ albumin, ↑ PT/INR, ↓ cholesterol

Cholestasis (obstructive)

• ↑↑ ALP
• ↑ GGT/bilirubin
• May be some mild ↑ ALT/AST

Disorder Unconjugated Conjugated ALT ALP GGT Synthetic DDx Comments Pre-hepatic (unconjugated) Jaundice ↑ ↔ ↔ ↔ ↔ ↔ All causes of haemolysis Unconjugated bilirubin does not enter urine, so urine is pale or dark from Hb Non-haemolytic (unconjugated) ↑ ↔ ↔ ↔ ↔ ↔ Gilbert’s syndrome (mild) Crigler-Najjar (rare but serious) Unconjugated bilirubin does not enter urine, so urine is pale or dark from Hb Hepatic (conjugated) ↔/↑ ↑ ↑↑ ↔ ↔ ↓ (if chronic) Viral Drugs Alcohol Cirrhosis Dark urine, pale stool May have hepatomegaly Post-hepatic (conjugated) ↔ ↑ ↑ ↑↑ ↑ ↔ Stones Strictures Masses (liver or pancreas) Pancreatitis Dark urine, pale stool Bone Disease ↔ ↔ ↔ ↑ ↔ ↔ Malignancy, Paget’s, CKD