American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the most common cause of hyporesponsiveness to erythropoietin?

1. Dehydration

2. Iron deficiency

3. Vitamin B12 deficiency

4. Chronic kidney disease

The correct answer is: Iron deficiency

The most common cause of hyporesponsiveness to erythropoietin is iron deficiency. Erythropoietin is a hormone produced by the kidneys that stimulates the production of red blood cells in the bone marrow. For this process to occur effectively, essential nutrients—including iron—must be available. Iron is vital for hemoglobin synthesis, and if a patient is iron deficient, the body struggles to produce adequate red blood cells, even in the presence of erythropoietin. In scenarios where erythropoietin is administered, if iron deficiency is present, the expected response (i.e., an increase in red blood cell production) will not occur, leading to a state of hyporesponsiveness. This condition is particularly relevant in patients with chronic kidney disease who may already have at least some degree of erythropoietin deficiency and might therefore require additional iron supplementation to respond adequately when erythropoietin is given. While other factors, such as dehydration or chronic kidney disease, can impact red blood cell production and anemia, their effects are not as directly related to the responsiveness to erythropoietin as iron deficiency. Understanding the importance of iron in hematopoiesis is crucial for addressing anemia effectively in clinical