Elevated WBC with metamyelocytes and myelocytes are seen. Which diagnosis is most likely?

• A. Acute Lymphoblastic Leukemia
• B. Acute Myeloid Leukemia
• C. Chronic Lymphocytic Leukemia
• D. Chronic Myelogenous Leukemia

Answer: (D)

A broad spectrum of granulocytic precursors in the blood, including metamyelocytes and myelocytes, points to a myeloproliferative process driving ongoing granulopoiesis. The classic condition with this pattern is chronic myelogenous leukemia, in which the BCR-ABL fusion protein causes unchecked production of granulocytes, leading to very high white blood cell counts and a left-shift that includes metamyelocytes and myelocytes in the peripheral smear.

In contrast, acute myeloid or acute lymphoblastic leukemias would typically show a high percentage of blasts rather than a wide range of maturing granulocytes. Chronic lymphocytic leukemia involves mature lymphocytes, not granulocytic precursors. A leukemoid reaction can show left-shifted neutrophils too, but it usually lacks the sustained, broad spectrum of granulocytic maturation and basophilia seen in CML, and it resolves with treatment of the underlying condition. Testing for the Philadelphia chromosome or BCR-ABL fusion can confirm CML.