18 Questions
Which type of bilirubin is tightly bound to albumin and not present in urine?
Unconjugated bilirubin
In which condition can conjugated bilirubin be found in urine while serum bilirubin levels are normal?
Acute viral hepatitis
What is a sensitive indicator of hepatocellular dysfunction in the urine?
Urobilinogen
Where is urobilinogen markedly increased?
Hemolysis
Which disease may show early signs of urobilinogen in the urine?
Acute viral hepatitis
Which type of hepatitis may have conjugated bilirubin in the urine while serum bilirubin levels are normal?
Acute viral hepatitis
What is the primary source of bilirubin?
Hemoglobin
What is the characteristic of conjugated bilirubin?
Water-soluble and binds to glucuronic acid
What is the result of high levels of unconjugated bilirubin in neonates?
Permanent brain damage
What is the cause of unconjugated hyperbilirubinemia in babies?
Hemolysis
What is the result of high levels of conjugated bilirubin excretion in urine?
Deep orange color
What is the characteristic of intrahepatic biliary obstruction?
Difficult to diagnose
What is the primary source of bilirubin in the human body?
Hemoglobin degradation from RBCs
Which condition is associated with an increase in conjugated bilirubin?
Biliary system obstruction
What is the process by which bilirubin becomes water-soluble?
Conjugation
Which test is most useful in differentiating between conjugated and unconjugated hyperbilirubinemia?
Serum bilirubin
Which condition is associated with an increase in unconjugated bilirubin?
Hemolysis
What is the purpose of liver function tests (LFTs) in evaluating response to therapy for autoimmune hepatitis?
To monitor response to therapy
Study Notes
Urine Bilirubin
- Presence of urine bilirubin indicates hepatobiliary disease
- Unconjugated bilirubin is tightly bound to albumin and not filtered by the glomerulus, thus not present in urine
- Measurable amounts of conjugated bilirubin in serum are found only in hepatobiliary disease
- Conjugated bilirubin may be found in urine when serum bilirubin levels are normal, particularly in early acute viral hepatitis
- Test strips impregnated with diazo reagent can detect as little as 1-2 mmol bilirubin/L
Urobilinogen
- Increase in urobilinogen in urine is a sensitive indicator of hepatocellular dysfunction
- Good indication of alcoholic liver damage, well-compensated cirrhosis, or malignant disease of the liver
- Appears early in viral hepatitis and is markedly increased in hemolysis
Bilirubin
- Derived from hemoglobin and cytochrome
- Normally conjugated with glucuronic acid
- Both conjugated and unconjugated bilirubin may be present in plasma
- Conjugated bilirubin is water-soluble, while unconjugated bilirubin is not and binds to albumin
- Neurotoxic and can cause permanent brain damage in neonates if levels rise too high
- Bilirubin metabolites are responsible for the brown coloration of feces
- Bilirubin in the gut is metabolized by bacteria to produce stercobilinogen, which is partly reabsorbed and re-excreted in the urine as urobilinogen
Causes of High Bilirubin Level
- Hemolysis (Haemolytic): Increased hemoglobin breakdown produces bilirubin, overloading the conjugating mechanism
- Liver disorder (Hepatocellular): Failure of the conjugating mechanism within the hepatocyte
- Obstruction in the biliary system (Cholestatic)
Liver Function Tests (LFTs)
- Helpful in follow-up of certain liver diseases and evaluating response to therapy, such as autoimmune hepatitis
- Limitations: Lack sensitivity and specificity
- Lack specificity and are not specific for any particular disease
- Serum albumin may be decreased in chronic disease and nephritic syndrome
- Aminotransferases may be raised in cardiac diseases and hepatic diseases
Classification of Liver Function Tests
- Tests of the liver's capacity to transport organic anions and to metabolize drugs: Serum bilirubin, urine bilirubin, urobilinogen
- Tests that detect injury to hepatocytes (serum enzyme tests): Aminotransferases, alkaline phosphatase, α-glutamyl transpeptidase, 5-nucleotidase, leucine aminopeptidase
- Tests of the liver's biosynthetic capacity: Serum proteins, albumin, prealbumin, serum ceruloplasmin, procollagen III peptide, α1-antitrypsin, alpha-fetoprotein, prothrombin time
Test your knowledge on the reference range for normal plasma bilirubin concentrations and the differences between conjugated and unconjugated bilirubin. Learn about the clinical significance of bilirubin in biochemistry.
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