American Board of Internal Medicine (ABIM) Certification Practice Exam

Which condition is characterized by slightly increased hemoglobin A2 and some residual hemoglobin F?

1. Iron deficiency anemia

2. β-thalassemia

3. Acute lymphoblastic leukemia

4. Autoimmune hemolytic anemia

The correct answer is: β-thalassemia

The condition characterized by slightly increased hemoglobin A2 and some residual hemoglobin F is β-thalassemia. This disorder is a genetic form of anemia resulting from reduced production of one of the components of hemoglobin. In β-thalassemia, the beta-globin chains are underproduced, leading to an imbalance in hemoglobin synthesis. As a compensatory mechanism, there is often an increase in the production of hemoglobin A2 (which is composed of two alpha and two delta chains) and sometimes residual hemoglobin F (composed of two alpha and two gamma chains) can be present. In β-thalassemia, individuals may have a mild increase in hemoglobin A2 levels (greater than 3.5% of total hemoglobin) and detectable levels of hemoglobin F due to the body trying to compensate for the lack of functional beta chains. This distinguishes β-thalassemia from other conditions like iron deficiency anemia, which typically does not feature these specific changes in hemoglobin composition, or acute lymphoblastic leukemia and autoimmune hemolytic anemia, which have different pathophysiological mechanisms and hematological profiles. Thus, the distinctive combination of slightly elevated hemoglobin A2 and the presence of hemoglobin F