Final answer:
The most likely diagnosis for a 60-year-old patient with fatigue and splenomegaly and abnormal CBC results is chronic myelogenous leukemia (CML).
Step-by-step explanation:
The most likely diagnosis for a 60-year-old patient presenting with fatigue and splenomegaly, along with a CBC revealing a WBC count of 24,000/microliter, Hgb of 13.5 g/dl, and Hct of 40, is chronic myelogenous leukemia (CML). CML is a type of leukemia that affects the myeloid line of leukocytes. It is characterized by the overproduction of young, immature leukocytes, leading to high WBC counts. Fatigue and splenomegaly are common symptoms of CML. Acute lymphocytic leukemia (ALL), acute myelogenous leukemia (AML), and chronic lymphocytic leukemia (CLL) do not typically present with splenomegaly. Therefore, CML is the most likely diagnosis in this case.