Pseudoplatelets in acute myeloid leukemia.

A 19-year-old man presented with fever and gum pain for 2 weeks. Physical examination revealed pallor, gingival hyperplasia, and cervical and axillary lymphadenopathy. Automated blood count demonstrated 115 3 10/mm white blood cells, 10.7 g/dL of hemoglobin, hematocrit 31.5%, and 42 3 10/mm platelets. Peripheral blood smear revealed 85% monoblasts and promonocytes (blast equivalents) as well as cytoplasmic leukemic cell fragments (arrows) mimicking platelets (arrowheads) (panel A and inset). The blasts and “pseudoplatelets” (arrow) stained for nonspecific esterase, confirming their monocytic leukemic origin, whereas platelets (arrowheads) were negative (panel B). The pseudoplatelets accounted for 20% of the platelets counted by the automated counter. Flow cytometry confirmed the diagnosis of acute monocytic leukemia.