49. Jaundice, distinct effects on bilirubin metabolism within each group to form diagnosis

Question 1

Outline the mechanism causing pre-hepatic jaundice

Answer 1

Increase RBC breakdown (haemolysis)
Increased haemoglobin breakdown
Increased production of bilirubin (UCB)

Question 2

List some of the causes of prehepatic jaundice

Answer 2

Tropical diseases e.g. yellow fever
Side effect of quinine based anti-malarial drugs
Genetic disorders associated with increased haemolysis (sickle cell anaemia)

Question 3

Describe physiological jaundice of the newborn and how does it arise?

Answer 3

After birth, newborns need to destroy foetal haemoglobin and replace with adult haemoglobin - RBCs have a short lifespan
Undeveloped liver has insufficient capacity to cope with elevated haemolysis due to lack of glucuronyl transferase
Breast milk also contains inhibitors of conjugation
Peaks at 3-5 days and lasts for over 14 days

Question 4

How is physiological jaundice of the newborn treated?

Answer 4

Phototherapy

- blue light changes unconjugated bilirubin into conjugated bilirubin (water soluble) so it can be excreted

Question 5

Describe how haemolytic disease of the newborn arises

Answer 5

Rh incompatibility between the mother and foetus can cause increased haemolysis
Rh- of mother is sensitised by Rh+ foetus of previous pregnancy or a Rh+ blood transfusion
Can cause very high bilirubin concentrations

Question 6

Babies with haemolytic disease of the newborn are at risk of kernicterus. What is this?

Answer 6

Bilirubin crosses the immature blood brain barrier and is deposited in basal ganglia and brainstem nuclei - can lead to brain damage if untreated

Question 7

How is haemolytic disease of the newborn treated?

Answer 7

High dose phototherapy and blood transfusion

Question 8

What are the three main issues which cause hepatic jaundice?

Answer 8

1. Impaired UCB uptake
2. Impaired conjugation of bilirubin (e.g. Gilbert’s syndrome)
3. Impaired transport of conjugated bilirubin into bile canaliculi (e.g. primary biliary colangitis - autoimmune destruction of small bile ducts)

Question 9

What are some of the causes of hepatic jaundice?

Answer 9

Viral hepatitis
Cirrhosis
Hepatotoxic drugs

Question 10

Define post-hepatic jaundice

Answer 10

Obstruction of the cystic, hepatic, or common bile ducts preventing bile from entering the small intestine

Question 11

What are the three main causes of post-hepatic jaundice?

Answer 11

1. Gallstones - small pebbles made of cholesterol that move from gallbladder and block bile ducts
2. Pancreatitis
3. Pancreatic tumours

Question 12

What causes the formation of gallstones?

Answer 12

When the capacity for bile salts and phospholipids to solubilise cholesterol is exceeded

Question 13

What are the effects of a cystic duct blockage?

Answer 13

Painful contractions

Question 14

What are the effects of a common bile duct blockage?

Answer 14

No bile secretion into gut
Steatorrhoea (fatty faeces with no bile salts)
Grey faeces (no bile pigments)
Post-hepatic jaundice (as no excretion of bilirubin)

Question 15

What are the effects of a blockage of the duodenal papilla?

Answer 15

No bile or pancreatic secretions into the intestines
Malnutrition (no digestion of contents)
Acute pancreatitis

Question 16

Why is it important that vitamin K is injected into patients with post-hepatic jaundice prior to surgery?

Answer 16

Bile salts are required for the absorption of fat soluble vitamins and for the digestion and absorption of lipids
Vit K is important in efficiency of coagulation cofactor gamma-glutamyl carboxylase (GGCX) in the liver
GGCX required for the production of many activated coagulation factors (II, VII, IX, X)
Vit K administration therefore prevents haemorrhage

Question 17

What reagent is used to test for serum C-bilirubin?

Answer 17

Diazo reagent (turns C-bilirubin blue - azobilirubin)

Question 18

What reagent(s) is used to test for total bilirubin in serum?

Answer 18

Diazo reagent AND caffeine

Caffeine displaces unconjugated bilirubin, unbinding it from albumin and making it water soluble to react with diazo

Question 19

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

Answer 19

Total bilirubin <21 micro mol/L

Conjugated bilirubin <7 micro mol/L

Question 20

How are bile pigments measured in urine?

Answer 20

Multistix urinalysis

Tests for urobilinogen and bilirubin (not UCB)

Question 21

What does it mean if there is conjugated bilirubin detected in the urine?

Answer 21

At low concentrations - normal
Otherwise, always a pathological finding as it means conjugated bilirubin has leaked back into the bloodstream (hepatic or post-hepatic jaundice)

Question 22

What does absence of urobilinogen in the urine indicate when there is a jaundiced patient?

Answer 22

Biliary obstruction

Question 23

What do high urobilinogen levels indicate in the urine?

Answer 23

Increased haemolysis or liver disease

Question 24

What does absence of stercobilin in faeces indicate?

Answer 24

Post-hepatic jaundice (can tell just by looking)

Question 25

What are blood gas analysers used for in some neonatal care units?

Answer 25

Allows early detection of jaundice and monitors severity/treatment
Based on absorbance of whole blood sample

Question 26

What are transcutaneous measurements used for?

Answer 26

Measure yellowness of skin due to bilirubin
Measures at various wavelengths to correct for variations in haemoglobin, melanin, and skin thickness
Not to be used as a substitute for lab measurements but can minimise the requirement for blood samples for monitoring