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Questions and Answers
What type of bilirubin is typically associated with hemolysis?
What type of bilirubin is typically associated with hemolysis?
What is the typical laboratory finding for urine bilirubin in a case of obstruction?
What is the typical laboratory finding for urine bilirubin in a case of obstruction?
Which of the following is NOT a special cause of hyperbilirubinemia?
Which of the following is NOT a special cause of hyperbilirubinemia?
What is a key feature of Kernicterus related to bilirubin levels?
What is a key feature of Kernicterus related to bilirubin levels?
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Which syndrome is characterized by decreased UDP-glucuronyltransferase function?
Which syndrome is characterized by decreased UDP-glucuronyltransferase function?
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What is the primary function of bilirubin in the body?
What is the primary function of bilirubin in the body?
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Which process converts unconjugated bilirubin into a more soluble form in the liver?
Which process converts unconjugated bilirubin into a more soluble form in the liver?
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What is the primary fate of urobilinogen produced in the intestines?
What is the primary fate of urobilinogen produced in the intestines?
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What condition is characterized by elevated levels of conjugated bilirubin leading to dark urine?
What condition is characterized by elevated levels of conjugated bilirubin leading to dark urine?
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In hemolysis, which type of bilirubin is primarily elevated in serum?
In hemolysis, which type of bilirubin is primarily elevated in serum?
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What is a common finding in urine during biliary obstruction?
What is a common finding in urine during biliary obstruction?
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How does the body primarily excrete bilirubin?
How does the body primarily excrete bilirubin?
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Which enzyme facilitates the conversion of unconjugated bilirubin into a more water-soluble form in the liver?
Which enzyme facilitates the conversion of unconjugated bilirubin into a more water-soluble form in the liver?
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What laboratory measurement indicates the presence of conjugated bilirubin in the urine?
What laboratory measurement indicates the presence of conjugated bilirubin in the urine?
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What is the first sign of jaundice that is often observed?
What is the first sign of jaundice that is often observed?
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What condition is most likely if both serum and urine bilirubin are high?
What condition is most likely if both serum and urine bilirubin are high?
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What happens to urobilinogen levels in the late stages of liver disease?
What happens to urobilinogen levels in the late stages of liver disease?
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What laboratory test can assess total bilirubin levels in the serum?
What laboratory test can assess total bilirubin levels in the serum?
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Study Notes
Bilirubin Overview
- Bilirubin is a byproduct of heme metabolism.
- It's produced in the liver.
- It's stored in the gallbladder.
- It's secreted into the duodenum after a meal.
- Primarily composed of water, phospholipids, and electrolytes.
- Bile salts are crucial for lipid absorption.
- Bilirubin is the body's method of excreting waste.
- It's a brown/yellow color.
Bilirubin Metabolism
- Heme is released from aged red blood cells and myoglobin, and cytochromes.
- Macrophages process residual heme.
- The heme is converted to biliverdin then to bilirubin.
Bilirubin in Blood
- Bilirubin has poor water solubility.
- It's transported through the bloodstream by albumin to the liver.
Bilirubin Conjugation in the Liver
- The liver conjugates bilirubin with glucuronic acid.
- UDP-glucuronyltransferase adds glucuronic acid to bilirubin, making it more soluble in water.
- Bilirubin monoglucuronide and bilirubin diglucuronide are water-soluble compounds.
- Increased water solubility allows excretion with bile.
Bilirubin Metabolism in the Intestines
- Bacteria convert bilirubin back to unconjugated bilirubin in the intestines.
- Enzymes called beta-glucuronidase facilitate this conversion.
- Unconjugated bilirubin is converted to urobilinogen.
- This takes place in the distal small intestine and colon.
Urobilinogen Fate
- Urobilinogen is excreted in feces (~80-90%); converted to stercobilin, which makes stool dark.
- A smaller portion (10-20%) is reabsorbed by the intestines.
- Most is taken up by the liver.
- A small amount is excreted in urine; converted to urobilin, which makes urine yellow.
Clinical Measurements of Bilirubin
- Van den Bergh reaction: Coupling bilirubin with a diazonium salt to form a colored complex.
- Serum conjugated bilirubin is water-soluble and can undergo the reaction directly.
- Serum unconjugated bilirubin is not water-soluble and must be mixed with alcohol before reacting.
- Urine bilirubin (conjugated only) is normally absent.
- Urine urobilinogen is typically present in small amounts.
Jaundice
- Jaundice is characterized by yellowing skin, conjunctiva, and mucous membranes.
- Scleral icterus (yellowing of the whites of the eyes) is often the first sign.
- Visible early in the area under the tongue.
- Normal total bilirubin is <1.0 mg/dL.
- Jaundice usually occurs when total bilirubin is >3.0 mg/dL.
Dark Urine
- Dark urine is associated with elevated conjugated bilirubin, which is water-soluble.
- Other causes of dark urine include rhabdomyolysis, hematuria, and dehydration.
Bilirubin Metabolism Clinical Assessment
- Serum bilirubin (total, direct, indirect)
- Urine urobilinogen
- Urine bilirubin (conjugated)
Hyperbilirubinemia
- This is an excess of bilirubin in the blood
- Possible causes include hemolysis, biliary obstruction, and liver disease.
Hyperbilirubinemia - Hemolysis
- ↑ heme from breakdown of RBCs.
- ↑ unconjugated bilirubin.
- No urine bilirubin (conjugated).
- Increased urine urobilinogen.
Hyperbilirubinemia - Biliary Obstruction
- Lack of bile flow (cholestasis).
- Extrahepatic (outside the liver): Gallstones, pancreatic mass.
- Intrahepatic (within the liver): Alcoholic liver disease, viral hepatitis.
- ↑ direct bilirubin.
- Clay-colored stools (lack of stercobilin).
- ↑ urine bilirubin.
- Absent urobilinogen.
Hyperbilirubinemia - Primary Liver Diseases
- Unconjugated hyperbilirubinemia: Significant damage to hepatocytes (liver cells). Chronic hepatitis, advanced cirrhosis.
- Conjugated hyperbilirubinemia: Damage to bile ducts. Viral hepatitis, alcoholic hepatitis, NASH.
Special Causes of Hyperbilirubinemia
- Rifampin/Probenecid: Competition for liver uptake; mild ↑unconjugated bilirubin.
- Gilbert's syndrome: ↓ UDP-glucuronyltransferase function; mild ↑ unconjugated bilirubin.
- Crigler-Najjar syndrome (type I and II): Severely reduced/absent UGT enzyme; ↑ unconjugated bilirubin.
- Dubin-Johnson syndrome: Defective liver excretion of conjugated bilirubin; ↑ conjugated bilirubin; black liver.
- Rotor's syndrome: Similar to Dubin-Johnson but without a black liver; milder.
- Neonatal jaundice: ↓ UDP-glucuronyltransferase enzyme activity in newborns leading to ↑unconjugated bilirubin.
Neonatal Jaundice Treatment
- Phototherapy exposes skin to specific wavelengths, converting bilirubin to lumirubin, which is more water-soluble and excreted easily.
Bilirubin Algorithm
- This is a diagnostic flowchart to determine the kind of bilirubin problem.
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Description
Dive into the world of bilirubin, a vital byproduct of heme metabolism that plays a crucial role in bile production and waste excretion. This quiz explores its metabolism, transport in the bloodstream, and conjugation processes in the liver. Test your knowledge on how bilirubin contributes to lipid absorption and overall health.
