Which of the following anemias causes a decrease in serum iron levels?

Iron-deficiency anemia is characterized by a decrease in serum iron levels. This condition arises when the body lacks sufficient iron to produce hemoglobin, the protein in red blood cells responsible for carrying oxygen. As a result, iron stores in the body become depleted, leading to low serum iron levels.

When diagnosing anemias, it is important to understand the cause of the deficiency. In iron-deficiency anemia, dietary insufficiency, blood loss, or malabsorption issues often lead to reduced serum iron levels. This is contrasted with other types of anemia, such as pernicious anemia, aplastic anemia, and hemolytic anemia, which do not primarily involve a lack of iron.

Pernicious anemia is often related to a deficiency of vitamin B12 due to impaired absorption, causing megaloblastic anemia rather than affecting serum iron levels. Aplastic anemia results from failure of the bone marrow to produce adequate blood cells, which is not directly linked to iron levels. Hemolytic anemia occurs when red blood cells are destroyed prematurely, which may actually lead to the release of iron into the bloodstream, not a decrease in serum iron levels.

Thus, the association of iron-deficiency anemia with decreased serum iron levels makes it the correct answer.