Which conditions are commonly associated with high mean corpuscular volume (MCV)?

High mean corpuscular volume (MCV) indicates that red blood cells are larger than normal, a condition known as macrocytosis. This phenomenon is frequently observed in cases of B12 or folate deficiency, as these vitamins play crucial roles in red blood cell production and maturation. When there is a deficiency of vitamin B12 or folate, there are disruptions in DNA synthesis that lead to abnormal red cell development, resulting in enlarged erythrocytes.

In contrast, conditions such as anemia of chronic disease, iron overload, and hemorrhagic shock typically do not present with an increase in MCV. Anemia of chronic disease often leads to microcytic anemia or normocytic anemia, depending on the underlying condition, but not macrocytosis. Iron overload primarily affects iron metabolism and typically does not increase the size of red blood cells, while hemorrhagic shock is characterized by decreased overall red cell mass due to blood loss, typically resulting in a decreased MCV rather than an elevated one. Therefore, the association of macrocytosis with B12 or folate deficiency makes this condition the correct answer regarding high MCV.