A 34-year-old man presents with gum bleeding, petechiae, and fatigue. CBC: WBC 2,100/μL, Hb 8.0 g/dL, platelets 18,000/μL. PT and aPTT are prolonged, fibrinogen is 80 mg/dL, and D-dimer is markedly elevated. Peripheral smear shows abnormal promyelocytes with Auer rods. Which is the most appropriate immediate step?

• A Give platelet and plasma transfusions and await karyotype results
• B Start all-trans retinoic acid immediately, before cytogenetic confirmation ✓
• C Start hydroxyurea to control the white count
• D Begin broad-spectrum antibiotics and repeat the smear in 48 hours

Explanation

The picture of promyelocytes with Auer rods, severe coagulopathy, and pancytopenia is acute promyelocytic leukaemia with t(15;17) generating PML-RARA. ATRA binds the fusion receptor and releases the differentiation block, and early initiation sharply reduces early death from DIC. Because untreated APL has high mortality within days, ATRA is started empirically on morphological suspicion without waiting for cytogenetics. Supportive transfusion alone (option A) leaves the differentiation block unaddressed and does not arrest the coagulopathy.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.