American Board of Internal Medicine (ABIM) Certification Practice Exam

In iron deficiency anemia, transferrin saturation is usually less than?

1. 15%

2. 25%

3. 30%

4. 10%

The correct answer is: 15%

In iron deficiency anemia, transferrin saturation is typically less than 15%. Transferrin is a protein that binds iron in the bloodstream and transports it to various tissues. In cases of iron deficiency, the body's iron stores are depleted, leading to a decrease in the levels of circulating iron. As a consequence, the quantity of transferrin that is saturated with iron is also reduced. Understanding transferrin saturation is critical in diagnosing and assessing the severity of iron deficiency anemia. When the iron stores are low, the transferrin saturation reflects how much of the available transferrin is occupied by iron. A saturation level less than 15% indicates a significant lack of iron for essential physiological functions, which aligns with the pathophysiology of iron deficiency anemia. Transferrin saturation levels above 15% may indicate that the body's iron stores are either adequate or excessive, which would not be consistent with iron deficiency anemia. Given this context, it is well established that in iron deficiency anemia, the saturation is characteristically found to be below this threshold, confirming the diagnosis of insufficient iron levels.