**Question:** Unconjugated hyperbilirubinemia of newborn is caused by all EXCEPT ___________

**Core Concept:**
Unconjugated hyperbilirubinemia, also known as neonatal jaundice, is a common condition in newborns characterized by increased levels of bilirubin, a yellow pigment produced during the breakdown of red blood cells. In newborns, unconjugated hyperbilirubinemia is primarily caused by immature liver function and inadequate bilirubin elimination. The liver plays a crucial role in conjugating bilirubin, which enables its excretion in the bile.

**Why the Correct Answer is Right:**
The correct answer, **D**, refers to a condition where bilirubin levels are increased due to an increase in the production of bilirubin. This is a separate condition from unconjugated hyperbilirubinemia, which is caused by immature liver function and inadequate bilirubin elimination. Conditions associated with increased bilirubin production include:

Option A: Hemolysis - This refers to the breakdown of red blood cells, which leads to increased bilirubin production. In contrast, unconjugated hyperbilirubinemia is caused by inadequate elimination of bilirubin.

Option B: Hemolytic jaundice - This is a specific type of jaundice caused by hemolysis. Again, this is different from unconjugated hyperbilirubinemia.

Option C: Gilbert's syndrome - This is a genetic disorder causing mildly elevated bilirubin levels due to reduced bilirubin conjugation. While Gilbert's syndrome may coexist with unconjugated hyperbilirubinemia, it does not cause unconjugated hyperbilirubinemia on its own.

**Why Each Wrong Option is Incorrect:**
Option A (hemolysis), B (hemolytic jaundice), and C (Gilbert's syndrome) are all conditions that can cause elevated bilirubin levels. However, they do not explain the unconjugated hyperbilirubinemia in newborns.

**Why the Correct Answer is Right:**
Conditions causing increased bilirubin production (A, B, C) do not explain the mechanism of unconjugated hyperbilirubinemia in newborns. Unconjugated hyperbilirubinemia is primarily due to immature liver function and inadequate elimination of bilirubin, which is why option D (immature liver function) is the correct answer. The immature liver in newborns is unable to efficiently conjugate bilirubin, leading to increased unconjugated bilirubin levels.

**Why Each Wrong Option is Incorrect:**
Option A (hemolysis), B (hemolytic jaundice), and C (Gilbert's syndrome) are conditions causing increased bilirubin levels but do not address the primary issue of immature liver function, which is responsible for unconjugated hyperbilirubinemia.

**Core Concept:**
Unconjugated hyperbilirubinemia in newborns is mainly due to the immature liver function, which is unable to efficiently conjugate bilirubin.