A 50-year-old man develops widespread petechiae and bleeding from venipuncture sites 10 days after receiving massive transfusion for trauma. Platelet count is 25,000/µL, PT and aPTT are mildly prolonged, and fibrinogen is low. Peripheral smear shows no schistocytes. Which mechanism best explains the thrombocytopenia?

• A Consumption from ongoing disseminated intravascular coagulation
• B Immune-mediated destruction from anti-HLA antibodies in donor plasma
• C Heparin-induced thrombocytopenia from intraoperative heparin use
• D Dilutional thrombocytopenia from transfusion of platelet-poor stored blood products ✓

Explanation

Massive transfusion (>1 blood volume in 24 hours) dilutes platelets and coagulation factors because stored packed red cells and FFP contain minimal functional platelets. Platelets degrade within 48 hours of storage. Dilutional coagulopathy is the most common cause of post-traumatic bleeding. The absence of schistocytes and timing (10 days) argue against DIC or HIT. TTP would present with MAHA and neurological symptoms.

Reference: Harrison's Principles of Internal Medicine, 20th ed.

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