Liver Function Tests (LFTs)

Question 1

Why are LFTs checked?

Answer 1

• Confirm liver injury or disease
• Distinguish between hepatic jaundice and post-hepatic or obstructive jaundice

Question 2

What blood tests are used to assess liver function?

Answer 2

• Alanine transaminase (ALT)
• Aspartate aminotransferase (AST)
• Alkaline phosphatase (ALP)
• Gamma-glutamyltransferase (GGT)
• Bilirubin
• Albumin
• Prothrombin time (PT)

Question 3

ALT

Answer 3

High ALT = marker of hepatocellular injury

(ALT is usually found in high concentrations within hepatocytes and enters the blood following hepatocellular injury)

Question 4

ALP

Answer 4

High ALP = (indirect) marker of cholestasis - look at GGT too

(ALP is particularly concentrated in the liver, bile duct and bone tissues. ALP is often raised in liver pathology due to increased synthesis in response to cholestasis)

Question 5

GGT

Answer 5

High GGT = suggests biliary epithelial damage and bile flow obstruction.

Also sometimes raised in response to alcohol or drugs.

Markedly raised ALP with raised GGT = probably cholestasis

Question 6

ALP (isolated)

Answer 6

No raised GGT? Maybe non-hepatobiliary pathology:

• Bony metastases or primary bone tumours (e.g. sarcoma)
• Vitamin D deficiency
• Recent bone fractures
• Renal osteodystrophy

Question 7

What if the patient is jaundiced but ALT and ALP levels are normal?

Answer 7

Check bilirubin - isolated rise suggests pre-hepatic jaundice

• Gilbert’s syndrome (more common)
• Haemolysis

Question 8

Albumin

Answer 8

Low albumin =

• Liver disease e.g. cirrhosis
• Inflammation

Question 9

Prothrombin time (PT)

Answer 9

High PT = liver disease / dysfunction