Which of the following is not the cause of macrocytic anaemia ?
**Core Concept**
Macrocytic anaemia is characterized by an increase in the mean corpuscular volume (MCV) of red blood cells, resulting in larger than normal cells. This can be caused by various factors that disrupt normal red blood cell production, including deficiencies in vitamin B12 and folate, which are essential for DNA synthesis and cell division.
**Why the Correct Answer is Right**
The correct answer will be a cause of normocytic or microcytic anaemia, as these conditions are characterized by a normal or decreased MCV. The underlying pathophysiology involves impaired heme synthesis, iron deficiency, or increased red blood cell destruction.
**Why Each Wrong Option is Incorrect**
* **Option A:** This could be a cause of macrocytic anaemia, as a deficiency in vitamin B12 or folate can disrupt DNA synthesis and cell division, leading to larger than normal red blood cells.
* **Option B:** Similarly, this could be a cause of macrocytic anaemia, as impaired DNA synthesis can result in larger than normal red blood cells.
* **Option C:** This could also be a cause of macrocytic anaemia, as a deficiency in vitamin B12 or folate can disrupt DNA synthesis and cell division, leading to larger than normal red blood cells.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that macrocytic anaemia can also be caused by certain medications, such as chloramphenicol, which inhibit protein synthesis and can lead to larger than normal red blood cells.
**Correct Answer: D.**