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Foundation Sciences · Biochemistry

Bilirubin Metabolism

⏱️ 45–60 minutes read 📖 Biochemistry

RBC haem → biliverdin → unconjugated bilirubin → hepatic UGT1A1 conjugation → biliary excretion → urobilinogen.

📌 Learning Objectives

  • Describe the key principles of bilirubin metabolism.
  • Explain the clinical relevance of bilirubin metabolism.
  • Recognise common conditions linked to bilirubin metabolism in MLA-style scenarios.

📋 Overview

RBC haem → biliverdin → unconjugated bilirubin → hepatic UGT1A1 conjugation → biliary excretion → urobilinogen. This topic integrates with pathology, pharmacology and clinical medicine and is frequently tested in UK medical school exams and the MLA.

🔬 Basic Science

RBC haem → biliverdin → unconjugated bilirubin → hepatic UGT1A1 conjugation → biliary excretion → urobilinogen. Detailed mechanisms, regulation and molecular interactions underpin both normal physiology and disease.

🏥 Clinical Relevance

Jaundice classification (pre/intra/post-hepatic); neonatal jaundice and kernicterus.

🧪 Investigations

Relevant laboratory tests, imaging or histological examination are used as appropriate to the clinical context.

💊 Management

Management is condition-specific; principles include addressing the underlying biochemical/structural derangement, supportive care and targeted therapy where available.

Revision Resources – expand the sections below for high-yield notes, exam pearls, key facts and further reading.

🎯 MLA High-Yield Notes & Quick Revision ⌄
High-yield topic for the UK MLA — frequently appears in SBA questions linking biochemistry concepts to clinical presentations and management decisions.
Applying biomedical science to clinical practice Diagnosis and investigation Pathophysiology of common conditions
  • RBC haem → biliverdin → unconjugated bilirubin → hepatic UGT1A1 conjugation → biliary excretion → urobilinogen.
⭐ Exam Pearls ⌄
⭐ High Yield
Unconjugated: albumin-bound, water-insoluble
Gilbert syndrome: mild UGT1A1 deficiency
Crigler-Najjar: severe UGT1A1 deficiency
Dubin-Johnson, Rotor: defective excretion (conjugated)
💡 Clinical Pearl
: Jaundice classification (pre/intra/post-hepatic); neonatal jaundice and kernicterus.
⚠️ Exam Tip — Common Mistakes
Confusing bilirubin metabolism with related but distinct mechanisms.
Memorising pathways without linking to clinical disease.
🔑 Key Facts ⌄
Unconjugated: albumin-bound, water-insoluble
Gilbert syndrome: mild UGT1A1 deficiency
Crigler-Najjar: severe UGT1A1 deficiency
Dubin-Johnson, Rotor: defective excretion (conjugated)
📚 References ⌄
  1. BMJ Best Practice
  2. Robbins Basic Pathology
  3. Lippincott Illustrated Reviews: Biochemistry
  4. Wheater's Functional Histology
  5. NICE guidance where applicable.

Further Resources

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