American Board of Internal Medicine (ABIM) Certification Practice Exam

Which method is used to diagnose chronic myeloid leukemia (CML)?

1. Bone marrow biopsy

2. Detection of the (9;22) translocation

3. Complete blood count alone

4. Determining serum lactate dehydrogenase

The correct answer is: Detection of the (9;22) translocation

The detection of the (9;22) translocation is a pivotal method for diagnosing chronic myeloid leukemia (CML). This specific genetic abnormality, known as the Philadelphia chromosome, results from a reciprocal translocation between chromosomes 9 and 22. This translocation leads to the formation of the BCR-ABL fusion gene, which encodes for a tyrosine kinase that drives the proliferation of myeloid cells and contributes to the pathogenesis of CML. While a bone marrow biopsy can provide valuable information about the cellularity and overall morphology of the marrow, it is not specific to CML and can be performed in various hematologic conditions. A complete blood count (CBC) can suggest the presence of CML through findings such as leukocytosis and the presence of immature granulocytes, but it cannot confirm the diagnosis on its own due to overlapping features with other disorders. Determining serum lactate dehydrogenase levels can indicate cellular turnover or tissue damage but is also not specific to CML and lacks the diagnostic specificity provided by identifying the (9;22) translocation. Thus, detecting the (9;22) translocation directly associates with the underlying biology of CML and confirms the diagnosis effectively, making it the