Question

In post-hepatic (obstructive) jaundice, the concentration of conjugated bilirubin in the blood is higher than that of unconjugated bilirubin because

• A. There is an increased rate of destruction of red blood cells.
• B. The unconjugated bilirubin is trapped by a bile stone produced in the bile duct.
• C. The conjugation process of bilirubin in the liver remains operative without any interference.
• D. The UDP-glucuronosyl-transferase activity is increased manifold in obstructive jaundice.

Hint:

In obstructive jaundice the block is after conjugation, so the liver keeps conjugating bilirubin normally, and it backs up into blood.

Answer 1

The Correct Option is C

This question tests the difference between the three types of jaundice: pre-hepatic (hemolytic), hepatic, and post-hepatic (obstructive). The clue is that conjugated bilirubin, not unconjugated, is high in the blood.

1. Increased red cell destruction: A higher breakdown rate of red blood cells would flood the liver with unconjugated bilirubin, faster than it can be conjugated, so unconjugated bilirubin would rise. This is the pattern of hemolytic jaundice, not obstructive jaundice, so this option does not fit.
2. Unconjugated bilirubin trapped by a bile stone: A stone in the bile duct sits after the conjugation step, so it can only trap bilirubin that has already been conjugated, not the unconjugated form. This statement mixes up which form gets trapped.
3. Conjugation process remains operative: In obstructive jaundice the liver cells and the conjugating enzyme are untouched, so bilirubin keeps getting conjugated at a normal pace. Since the duct beyond the liver is blocked, this newly conjugated bilirubin has nowhere to go and spills back into the blood, which is exactly why the conjugated fraction dominates.
4. Increased UDP-glucuronosyl-transferase activity: There is no known rise in this enzyme's activity during duct obstruction, the enzyme works at its baseline rate, the problem is purely a blocked exit route.

The correct explanation is that conjugation continues normally in the liver cells, so the bilirubin reaching the blood is mainly in its conjugated form. This matches statement (C).

Let's summarize:

• Obstructive jaundice blocks the path after conjugation, so conjugated bilirubin regurgitates into blood.
• Hemolytic jaundice raises unconjugated bilirubin because red cell breakdown outpaces the liver's conjugating capacity.

So the reason conjugated bilirubin dominates in post-hepatic jaundice is that the conjugation step in the liver keeps working without interference.