Liver function tests

Question 1

Give the four main functions of the liver

Answer 1

Synthesis
Detoxification
Immune function
Storage

Question 2

What compounds does the liver synthesise?

Answer 2

Clotting factors
Bile acids
Carbohydrates (glucose, glycogen)
Proteins (albumin)
Lipids (cholesterol, lipoprotein, tryglyceride)
Hormones (angiotensinogen, insulin-like growth factor)

Question 3

Describe the detoxification function of the liver

Answer 3

Urea production from ammonia
Detoxification of drugs (e.g. alcohol)
Bilirubin metabolism from breakdown of haemoglobin
Breakdown of insulin and other hormones

Question 4

Describe the immune function of the liver

Answer 4

Combating infection (primarily infectious particles that are absorbed through the gut wall or from arterial blood)
Cleaning blood of particles/infections including bacteria
Neutralising and destroying drugs and toxins

Question 5

What compounds does the liver store?

Answer 5

Glycogen
Vitamins A, D, B12, K
Copper, Iron

Question 6

List the main liver function tests

Answer 6

Bilirubin
Aminotransferases
Alkaline phosphate
Gamma GT
Albumin
Prothrombin time
Creatinine
Platelet count

Question 7

What is the normal range for bilirubin?

Answer 7

1-20umol/L

Question 8

What is the normal range for albumin?

Answer 8

35-50g/L

Question 9

What are the normal ranges for aminotransferase enzymes?

Answer 9

5-55 U/L

Question 10

Which two aminotransferase enzymes are tested for? What is the main difference between them?

Answer 10

Alanine aminotransferase (ALT)
Aspartate aminotransferase (AST)

ALT is very specific to liver disease whereas AST can indicate muscle damage elsewhere in the body

Question 11

Where is bilirubin produced?

Answer 11

In the spleen (by macrophages)

In the liver (Kupfer cells)

Question 12

Give the main causes of raised serum bilirubin

Answer 12

Prehepatic: excessive RBC breakdown

Hepatic: parenchymal damage, e.g. by alcohol, cirrhosis, hepatitis

Post-hepatic: obstruction of the bile duct

Question 13

What might be indicated by altered albumin levels?

Answer 13

Low albumin: chronic liver disease (although there are other causes e.g. renal disease, malnutrition/malabsorption, severe inflammation/shock)

High albumin: dehydration

Question 14

What is the normal range for alkaline phosphatase (ALP)?

Answer 14

30-130 U/L

Question 15

When would Gamma GT level be considered raised?

Answer 15

When it is higher than 35 U/L

Question 16

Where are aminotransferases normally found, and what does it suggest if serum levels are raised?

Answer 16

Usually found inside the hepatocytes
Therefore raised serum levels indicates liver damage, e.g. in chronic liver disease or cirrhosis
Levels are very high in hepatitis; can be 20-50 times higher than normal

Question 17

Describe how aminotransferase ratios can indicate disease

Answer 17

ALT > AST indicates chronic liver disease
AST > ALT indicates cirrhosis
Ratio >2 suggests alcoholic liver disease

Question 18

Explain the meaning of increased alkaline phosphatase (ALP) in the plasma

Answer 18

Usually means damage to the lining of the bile duct or to bone (ALP is found in large concentrations in these cells)
Largely elevated in bile duct obstruction (or injury)
Slightly raised in liver disease

Question 19

What test is done alongside ALP to distinguish between liver/biliary disease and bone disease?

Answer 19

Gamma GT; if GGT is normal then raised ALP is most likely to be caused by bone disease

Question 20

What is prothrombin time a marker of?

Answer 20

Synthetic function of the liver:
The liver synthesises and secretes clotting factors, so if it’s failing, levels of clotting factors will decrease and prothrombin time will increase

Question 21

Give a use for testing prothrombin time

Answer 21

Useful in staging liver disease to distinguish whether a patient is in need of a transplant

Question 22

What is the most likely cause of jaundice if Alkaline Phosphatase (ALP) is raised?

Answer 22

Obstructive (post-hepatic) jaundice

e.g. gallstones, stricture, sclerosing cholangitis, pancreatitis, tumour blocking the bile duct.

Question 23

What test (besides serum bilirubin) can be done to diagnose hepatic and post-hepatic jaundice?

Answer 23

Urinary bilirubin

• may be high in hepatic
• high post-hepatic
• no urinary bilirubin in pre-hepatic jaundice

Question 24

What investigation should always be done in a patient presenting with jaundice?

Answer 24

Abdominal ultrasound