American Board of Internal Medicine (ABIM) Certification Practice Exam

What characterizes a delayed hyperhemolytic transfusion reaction?

1. Immediate hemolysis after transfusion

2. A sudden drop in hemoglobin level with reticulocytosis

3. Increased platelet count

4. High creatinine levels

The correct answer is: A sudden drop in hemoglobin level with reticulocytosis

A delayed hyperhemolytic transfusion reaction is primarily characterized by a sudden drop in hemoglobin levels accompanied by reticulocytosis several days to weeks after the transfusion. This occurs due to an immune response in which the recipient's immune system identifies the transfused red blood cells (RBCs) as foreign and begins to destroy them over time. The reticulocytosis indicates an increased production of red blood cells by the bone marrow as a compensatory response to the hemolysis occurring in the body, reflecting the ongoing recovery effort against the anemia caused by the transfusion reaction. In contrast, immediate hemolysis after transfusion suggests an acute hemolytic reaction, which does not align with the delayed nature of this specific reaction. Increased platelet count or high creatinine levels are not typical features of a delayed hyperhemolytic transfusion reaction; instead, these findings could indicate other conditions, such as thrombotic microangiopathy or acute kidney injury. Therefore, the key characteristic of this delayed reaction is the drop in hemoglobin with reticulocytosis following the transfusion.