**Question:** A normal MCV would be expected in a patient with which one of the following conditions?

A. Sickle cell anemia
B. Thalassemia
C. Iron deficiency anemia
D. Polycythemia

**Core Concept:** Mean Corpuscular Volume (MCV) is a measure of the size of red blood cells (RBCs) and is calculated as a part of complete blood count (CBC) test. A normal MCV value ranges from 80-100 fL (femtoliters).

**Why the Correct Answer is Right:** A normal MCV indicates non-anemic conditions where RBCs are of normal size. In the given options, only D. Polycythemia is a condition characterized by increased RBC mass due to excessive erythropoietin production or reduced RBC destruction. As a result, the RBCs are larger than normal, leading to an elevated MCV value.

**Why Each Wrong Option is Incorrect:**

A. Sickle cell anemia (SCA) has a low MCV due to abnormal hemoglobin production and RBCs that are shorter and broader than normal, thus reducing their volume.
B. Thalassemia is a group of inherited blood disorders characterized by abnormal hemoglobin production and also results in low MCV values due to smaller RBCs.
C. Iron deficiency anemia is caused by reduced red blood cell production due to insufficient iron levels. It leads to smaller RBCs and a low MCV value.

**Clinical Pearl:** Understanding MCV values is essential for diagnosing and monitoring various hemoglobinopathies and anemias. A normal MCV value in a patient helps to exclude the presence of anemia and its associated complications.

**Correct Answer:** D. Polycythemia