Hypercellular bone marrow of a CML patient
A complete blood count can reveal some key identifying features of CML. The most notable feature is a drastically increased white blood cell (WBC) count, typically well over 100 x 109/L (adult reference range approximately 4.5 - 11.0 x 109/L). Patients may have an increased platelet count, a reduced red blood cell (RBC) count, and moderate decrease in hemoglobin. Peripheral blood smears exhibit a left shift with increased neutrophils and myelocytes. Blast cells do not exceed 20% in most cases. Elevations in eosinophils, basophils, and monocytes can be observed along with an occasional pseudo-Pelger-Huet phenomenon. Micromegakaryocytes have also been observed on CML differentials.
Although not as common in today's laboratories, leukocyte alkaline phosphatase (LAP) scores can be helpful in differentiating CML from other conditions appearing similar in morphology, such as a leukemoid reaction. LAP scores are low with CML and high with leukemoid reaction. Note that CML always has a low LAP score. However, a low LAP score does not always indicate the presence of CML (ie, a low LAP score is not specific for CML). Most laboratories now utilize cytogenetic and molecular diagnostics to diagnose CML. The presence of the Philadelphia chromosome can aid in further differentiating CML from other myeloproliferative disorders that can have overlapping symptoms or laboratory findings.
Bone marrow analysis shows marked hypercellularity with a very high myeloid:erythroid ratio (up to 50:1) due to the increased production of myeloid cells. There are less than 20% blasts and no leukemic hiatus.
Serum uric acid and lactate dehydrogenase are often increased due to the rapid cell turnover associated with this condition.