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 auto mated platelet counts in therapy-related, secondary acute monocytic leukemi a. The first patient was a 69-year-old man with large cell carcinoma of the lung who developed acute monocytic leukemia 11/2 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 monocyt ic leukemia 11/2 year after initiation of chemotherapy for her lymphoma. Pl atelet counts were determined by the automated Coulter (STKS) counter. Both patients had clinical and laboratory evidences of tumor lysis syndrome and disseminated intra-vascular coagulation. The peripheral blood smears revea led numerous fragments of leukemic cells and apoptotic cells with pyknotic nuclei. The Coulter machine enumerated these cellular fragments as platelet s, resulting in falsely elevated platelet counts. Awareness of this laborat ory artifact in secondary acute monocytic leukemia with tumor lysis syndrom e is important so that potential life-threatening thrombocytopenia is not o verlooked.