GI Liver Function Tests

Question 1

What are the “true” tests of liver function in LFTs?

Answer 1

Synthetic functions:
- Albumin
- Clotting factors (e.g., prothrombin time)
- Glucose

Excretory function:
- Bilirubin

Question 2

Why are AST and ALT not considered “true” liver function tests?

Answer 2

They indicate liver damage, not liver function.

Question 3

What other tissues can release AST?

Answer 3

Cardiac muscle

Skeletal muscle

Kidneys

Red blood cells

Question 4

What is the significance of the AST/ALT ratio?

Answer 4

ALT > AST: Viral or drug-induced hepatitis

AST > ALT: Alcoholic hepatitis or cirrhosis

Question 5

What does a raised ALP with a normal GGT suggest?

Answer 5

A bone source of ALP elevation.

Question 6

What does raised ALP with raised GGT suggest?

Answer 6

A biliary source of enzyme elevation.

Possible causes:

Biliary obstruction

Infiltration

Congestion

Question 7

What are the two main patterns of abnormal liver function test results?

Answer 7

Obstructive (cholestatic):

High bilirubin
High ALP
Normal ALT/AST

Hepatic (inflammatory):

High ALT (200–2000 U/L)
Variable bilirubin elevation
Slightly raised ALP (<2x normal)
Increased PT/INR

Question 8

What are some limitations of LFT interpretation?

Answer 8

Patterns aren’t always definitive.

Hepatocellular injury may release bilirubin.

Obstruction can cause secondary hepatocellular damage.

Question 9

What is the role of GGT in LFT interpretation?

Answer 9

Helps confirm biliary origin when ALP is elevated.

Isolated GGT elevation is nonspecific.

Question 10

When might isoenzymes be useful in interpreting LFTs?

Answer 10

Rarely needed.

Can help differentiate between liver and bone sources of ALP elevation.

Question 11

What can prolonged PT/INR indicate in liver disease?

Answer 11

Synthetic failure due to reduced clotting factor production.