ASCP Specialist in Hematology (SH) Practice Exam 2025 – Your All-in-One Guide to Exam Success!

In the context of chronic myelogenous leukemia (CML), the presence of the Philadelphia chromosome is a key hallmark. This specific genetic abnormality arises from a reciprocal translocation between chromosomes 9 and 22, leading to the fusion of the BCR and ABL genes. This fusion creates an active tyrosine kinase that drives the proliferation of myeloid cells, which is characteristic of CML.

While increased white blood cell count, presence of basophils, and high platelet count can all be observed in CML, the Philadelphia chromosome is a definitive marker used in the diagnosis and classification of this leukemia. Identifying this chromosomal abnormality helps to confirm the diagnosis and to distinguish CML from other types of leukemias, as well as guiding treatment decisions, including the use of targeted therapies such as tyrosine kinase inhibitors. Thus, the Philadelphia chromosome is considered the hallmark of CML in blood tests.