All-trans retinoic acid (ATRA) should be administered as soon as possible, followed by chemotherapy, for this patient with acute promyelocytic leukemia (APL). APL is a clinically and biologically distinct variant of acute myelocytic leukemia characterized by the presence of a (15;17) gene translocation, which gives rise to the promyelocytic leukemia–retinoic acid receptor-α fusion transcript and arrest of leukemic cells at the promyelocyte stage. Adding ATRA to standard induction and consolidation chemotherapy releases the block in promyelocyte maturation and produces cure in up to 80% of patients. If APL is suspected, ATRA should be initiated without waiting for confirmation. This patient's symptoms and laboratory studies strongly suggest APL, with prominent Auer rods on the peripheral blood smear and bleeding out of proportion to thrombocytopenia. She also has biochemical evidence of disseminated intravascular coagulation, which is a defining clinical clue to APL. In addition to appropriate blood product transfusion support, early ATRA administration is required to help patients survive induction chemotherapy. The greatest mortality risk from APL accrues in the first 2 weeks, with delay in ATRA administration being one of several root causes.

Testing for the t(9;22) would not be helpful in this patient, because it would identify the Philadelphia chromosome, which only has relevance in chronic myeloid leukemia or acute lymphoblastic leukemia.

Testing for the t(15;17) would confirm a diagnosis of APL and can be accomplished in less than 24 hours using fluorescence in situ hybridization. However, enough clinical clues are already provided to strongly suspect the diagnosis, and ATRA should be initiated at the point of clinical suspicion to improve early survival.