In which situation would the MCV typically be decreased?

A decreased mean corpuscular volume (MCV) is typically associated with microcytic anemias, the most common of which is iron deficiency anemia. In this condition, the body lacks sufficient iron to produce hemoglobin, leading to the formation of smaller-than-normal red blood cells (microcytes). This reduction in size directly results in a decreased MCV value.

Iron deficiency anemia is characterized by low hemoglobin levels, low ferritin, and increased total iron-binding capacity, all of which indicate insufficient iron stores in the body. The smaller red blood cells produced in response to this deficiency are unable to carry oxygen efficiently, contributing to the symptoms of anemia.

In contrast, other situations such as chronic dehydration may lead to an increased MCV due to a relative increase in plasma volume, while hemolytic anemias often present with normocytic red blood cells with a normal or slightly elevated MCV. Macrocytic anemias, as indicated by their name, have increased MCV due to larger red blood cells often resulting from deficiencies in vitamin B12 or folate. Thus, iron deficiency anemia distinctly stands out as the primary condition associated with a decreased MCV.