American Board of Internal Medicine (ABIM) Certification Practice Exam

How many lymphoblasts in the blood or bone marrow indicates a diagnosis according to standard criteria?

1. 5%

2. 10%

3. 25%

4. 50%

The correct answer is: 25%

A diagnosis of acute lymphoblastic leukemia (ALL) is often made when the percentage of lymphoblasts in the blood or bone marrow meets certain criteria established by hematologic guidelines. According to standard criteria, the presence of 20% or more lymphoblasts in the bone marrow is typically used as a threshold for diagnosis. Focusing on the provided options, the choice suggesting 25% aligns closely with this diagnostic criterion, as it indicates a significant level of lymphoblasts that would raise suspicion for leukemia. This percentage demonstrates that there is a substantial proliferation of lymphoblasts, which is characteristic of acute leukemia. On the other hand, lower percentages, such as 5%, 10%, or even 20%, may not provide sufficient evidence for a diagnosis of ALL, given that they can be observed in other benign or reactive processes. Thus, 25% is recognized as a point where it becomes clinically relevant, warranting further investigation and consideration for a definitive diagnosis.