Spurious elevation of automated platelet counts in secondary acute monocytic leukemia associated with tumor lysis syndrome.

The intent of this article is to describe the effect of tumor lysis on automated platelet counts in therapy-related, secondary acute monocytic leukemia. The first patient was a 69-year-old man with large cell carcinoma of the lung who developed acute monocytic leukemia 1(1/2) years after initiation of radiation and chemotherapy for his carcinoma. The second patient was a 72-year-old female with peripheral T-cell lymphoma who developed acute monocytic leukemia 1 year after initiation of chemotherapy for her lymphoma. Platelet counts were determined by the automated Coulter (STKS) counter. Both patients had clinical and laboratory evidences of tumor lysis syndrome and disseminated intravascular coagulation. The peripheral blood smears revealed numerous fragments of leukemic cells and apoptotic cells with pyknotic nuclei. The Coulter machine enumerated these cellular fragments as platelets, resulting in falsely elevated platelet counts. Awareness of this laboratory artifact in secondary acute monocytic leukemia with tumor lysis syndrome is important so that potential life-threatening thrombocytopenia is not overlooked.