Bilirubin Metabolism

Question 1

What are the reference ranges for total and conjugated bilirubin in an adult?

Answer 1

Total Bilirubin = <21micromol/L

Conjugated Bilirubin = <7micromol/L

Question 2

Which enzyme conjugates Bilirubin in the Hepatocytes of the liver?

Answer 2

UDP Glucuronyl Transferase

Question 3

Which enzyme converts Haem to Biliverdin?

Answer 3

Haem Oxygenase

Question 4

Which enzyme converts Biliverdin to Bilirubin?

Answer 4

Bilirubin Reductase

Question 5

At what ranges would you see Jaundice?

Answer 5

>30micromol/L = jaundice may be visible in the sclera
>100micromol/L = jaundice may be visible in the skin

Question 6

What is kernicterus

Answer 6

When bilirubin crosses the immature blood brain barrier in newborns and there is deposition of bilirubin in basal ganglia and brainstem nuclei, resulting in brain damage if left untreated. The treatment is high dose phototherapy and blood transfusion. This can occur in haemolytic disease of the newborn.

Question 7

In what ways can hepatic jaundice occur?

Answer 7

• Impaired uptake of unconjugated bilirubin
• Impaired conjugation of bilirubin - e.g. Gilberts (reduced glucuronyl transferase activity)
• Impaired transport of conjugated bilirubin into bile canaliculi - e.g. primary biliary cholangitis (autoimmune destruction of the small bile ducts)
• Liver Damage

Question 8

Describe what would be seen in Pre-Hepatic jaundice.

Answer 8

• Increased Unconjugated bilirubin in plasma/serum
• Normal/Increased Conjugated bilirubin in plasma/serum
• Conjugated bilirubin absent from urine
• Increased urobilin in urine
• Increased stercobilin in faeces

Question 9

Describe what would be seen in Hepatic jaundice.

Answer 9

• Increased unconjugated bilirubin in plasma/serum
• Increased conjugated bilirubin in plasma/serum
• Conjugated bilirubin present in urine
• Increase in urobilin in urine
• No chance in stercobilin in faeces

Question 10

Describe what would be seen in Post-hepatic jaundice.

Answer 10

• Normal unconjugated bilirubin in plasma/serum
• Increased conjugated bilirubin in plasma/serum
• Increased conjugated bilirubin in urine
• No urobilin in urine
• No stercobilin in faeces -> steatorrhoea

Question 11

What is the normal concentration of conjugated bilirubin?

Answer 11

<7micromol/L

Question 12

What is the normal concentration of total bilirubin?

Answer 12

<21micromol/L

Question 13

What is used to displace unconjugated bilirubin from albumin to test total concentration of bilirubin?

Answer 13

Caffeine

Question 14

What is conjugated bilirubin in the urine indicative of?

Answer 14

It is always pathological as it means conjugated bilirubin has leaked out into the systemic circulation. This is seen in hepatic and post-hepatic jaundice.

Question 15

What does the test area contain on urinalysis for Bilirubin?

Answer 15

Diazide

Question 16

What does the test area contain on urinalysis for Urobilinogen?

Answer 16

p-dimethylaminobenzaldehyde - forms pink dye in presence of urobilinogen. Urobilinogen is normally present in low concentrations, high concentrations can indicate increased haemolysis or liver disease (pre-hepatic or hepatic jaundice).

Question 17

What does high Alkaline Phosphatase indicate?

Answer 17

Cholestasis

Question 18

What does Low Albumin suggest?

Answer 18

Chronic Liver Disease

Question 19

What are raised anti-mitochondrial antibodies indicative of?

Answer 19

Primary Biliary Cholangitis (Hepatic Jaundice)