Laboratory tests that distinguish Polycythemia Vera (PV) from Chronic Myelogenous Leukemia (CML) include all of the following EXCEPT?

Understanding the distinctions between Polycythemia Vera (PV) and Chronic Myelogenous Leukemia (CML) is key in hematology. The correct answer, hypercellular bone marrow, is characteristic of various myeloproliferative disorders, including both PV and CML. Therefore, hypercellularity alone does not help differentiate between these two conditions.

In contrast, the JAK2 mutation is a crucial marker primarily associated with PV and is found in about 95% of patients with this condition, while it is typically absent in CML. The presence of nucleated red blood cells can suggest PV, where erythropoiesis is increased, but is less specific for CML, where myeloid proliferation is prominent. The elevated leukocyte alkaline phosphatase (LAP) score is another distinguishing factor; it is usually high in PV due to increased granulocyte production and low in CML, where the leukocytes are often immature and have less alkaline phosphatase activity.

By focusing on the specifics of the conditions, hypercellular bone marrow cannot effectively serve as a differentiator between PV and CML, as both can present with such findings.