Bilirubin

Aka: Bilirubin, Total Bilirubin, Serum Bilirubin, Hyperbilirubinemia

1. See Also
   1. Jaundice
   2. Direct Bilirubin (Conjugated Bilirubin)
   3. Indirect Bilirubin (Unconjugated Bilirubin)
   4. Neonatal Bilirubin
   5. Liver Function Test
   6. Liver Function Test Abnormality
2. Physiology
   1. Heme product degradation yields Hemoglobin
      1. Red Blood Cells (responsible for 80% of heme product)
      2. Myoglobin
      3. Maturing Red Blood Cells
   2. Hemoglobin transported to reticuloendothelial system
      1. Hemoglobin bound to Haptoglobin in plasma
      2. Hemoglobin metabolized in reticuloendothelial system
         1. Heme is oxidized to bilverdin
         2. Iron
         3. Globin
   3. Bilverdin converted to Unconjugated Bilirubin
      1. Normal production of Bilirubin: 4 mg/kg/day
   4. Unconjugated Bilirubin circulates
      1. Tightly bound to albumin and fat soluble
         1. Displaced Bilirubin causes
            1. Albumin saturated with Bilirubin or
            2. Medications (e.g. Sulfisoxazole, Streptomycin, Vitamin K)
         2. Displaced Unconjugated Bilirubin crosses blood-brain barrier and placenta
            1. Results in toxicity (e.g. Hepatic Encephalopathy, Kernicterus)
      2. Unconjugated Bilirubin is insoluble in water
         1. Not found in tears or Saliva
         2. Unconjugated Bilirubin can not be excreted
      3. Concentrates in high albumin containing tissues
         1. Skin (especially face and trunk): Jaundice
         2. Sclera: Scleral Icterus
   5. Unconjugated Bilirubin converts to Conjugated Bilirubin
      1. Bilirubin conjugated with glucuronic acid in liver
         1. Conjugated by glucuronosyltransferase enzyme
      2. Conjugated Bilirubin is water soluble
      3. Only Conjugated Bilirubin can be excreted
   6. Conjugated Bilirubin excreted into biliary tract
      1. Stored in gallbladder
      2. Ultimately excreted into duodenum
   7. Conjugated Bilirubin passes into feces
      1. Converted by bacterial enzymes to Urobilinogen
      2. Most Urobilinogen excreted in stool
      3. Small levels Urobilinogen reabsorbed and urinated
3. Normal
   1. Total Bilirubin <1.0 mg/dl
4. Increased Total Bilirubin
   1. Diagnosis depends on whether Bilirubin is conjugated
      1. See Unconjugated Bilirubin (Hemolytic Jaundice)
      2. See Conjugated Bilirubin (Obstructive Jaundice)
   2. General Hyperbilirubinemia Causes
      1. See Medication Causes of Jaundice
      2. Hemolysis
      3. Liver disease
         1. Hepatitis
         2. Cirrhosis
         3. Liver tumor
         4. Cholangitis
         5. Biliary Tract Obstruction
         6. Epstein Barr Virus (EBV)
         7. Cytomegalovirus (CMV)
         8. Hereditary
            1. Gilbert's disease
            2. Dubin-Johnson syndrome
         9. Congestive Heart Failure
            1. Hepatic congestion
      4. Pulmonary Causes
         1. Pulmonary infarction
         2. Pulmonary Embolus