Question

A $38$-year-old man is evaluated in the emergency department for progressive fatigue, severe epistaxis, and bleeding from his gums over the past two days. He has no significant past medical history and takes no medications. Vital signs are: Temperature $37.6^\circ\text{C}$ ($99.7^\circ\text{F}$), Blood pressure $100/60 \text{ mm Hg}$, Heart rate $112/\text{min}$, Respiratory rate $18/\text{min}$. Physical examination reveals marked mucosal pallor, continuous gingival oozing, and extensive coalescing petechiae and purpura over the trunk and bilateral lower extremities. Laboratory studies show:

Leukocyte count: $2,800/\text{mm}^3$
- Neutrophils: $15\%$
- Lymphocytes: $25\%$
- Atypical cells: $60\%$
Hemoglobin: $7.4 \text{ g/dL}$
Platelet count: $15,000/\text{mm}^3$
Prothrombin time: $24 \text{ seconds}$
Partial thromboplastin time: $54 \text{ seconds}$
Fibrinogen: $65 \text{ mg/dL}$ (Normal: $150-400 \text{ mg/dL}$)
D-dimer: $8,500 \text{ ng/mL}$ (Normal: $< 500 \text{ ng/mL}$)

Peripheral blood smear demonstrates predominant cells with bilobed nuclei and dense, coarse azurophilic granules. Several of these cells contain bundles of red-staining, needle-like cytoplasmic inclusions. Which of the following is the most appropriate initial step in the management of this patient?