All of the following statements about macrocytic anemias are true EXCEPT:

Explanation

## Macrocytic Anemias: Megaloblastic vs. Non-Megaloblastic **Key Point:** Macrocytic anemias are divided into two categories: **megaloblastic** (abnormal nuclear maturation) and **non-megaloblastic** (normal nuclear maturation). ### Classification of Macrocytic Anemias ```mermaid flowchart TD A[Macrocytic Anemia<br/>MCV > 100 fL] --> B{Megaloblastic?} B -->|Yes| C[B12 deficiency<br/>Folate deficiency<br/>Drug-induced] B -->|No| D[Reticulocytosis<br/>Hemolysis<br/>Liver disease<br/>Hypothyroidism<br/>Alcohol abuse] C --> E[Nuclear-cytoplasmic<br/>asynchrony] D --> F[Normal nuclear<br/>maturation] ``` **High-Yield:** Reticulocytosis causes macrocytosis because reticulocytes are larger than mature RBCs (they contain residual RNA). However, reticulocytosis is **non-megaloblastic** — nuclear maturation is normal. ### Megaloblastic vs. Non-Megaloblastic Features | Feature | Megaloblastic | Non-Megaloblastic | | --- | --- | --- | | Nuclear-cytoplasmic asynchrony | Present | Absent | | Cause | B12/folate deficiency, drugs | Reticulocytosis, hemolysis, liver disease | | Hypersegmented neutrophils | Yes | No | | Bone marrow | Giant metamyelocytes, abnormal mitosis | Normal maturation | | MCV elevation | Marked (>100 fL) | Mild to moderate | **Clinical Pearl:** Hypersegmented neutrophils (>5 lobes) are a hallmark of megaloblastic anemia and occur in both B12 and folate deficiency due to impaired DNA synthesis affecting all dividing cells. ### Why Option 3 Is Wrong Reticulocytosis causes macrocytosis but is **NOT megaloblastic**. Reticulocytes are larger because they contain residual RNA and ribosomes, not because of abnormal nuclear maturation. This is a critical distinction in anemia classification.