In iron deficiency anemia, transferrin saturation is typically:

• A. Decreased
• B. Increased
• C. Normal
• D. Variable

Answer: (A)

Transferrin saturation reflects the proportion of transferrin binding sites actually bound by iron, calculated as serum iron divided by total iron-binding capacity (TIBC) times 100. In iron deficiency anemia, circulating iron falls because iron stores are depleted, while the liver increases transferrin production, raising TIBC. With less iron available but more binding sites, a smaller fraction of transferrin is iron-bound, so transferrin saturation decreases. This pattern helps distinguish iron deficiency from other causes of low iron, where the saturation would not be as reduced (for example, iron overload would raise saturation, and inflammatory states can lower iron with variable effects on TIBC).