A 28-year-old multiparous woman at 38 weeks gestation presents with vaginal bleeding and abdominal pain. She delivers a stillborn infant 4 hours later. Postpartum, she has severe ongoing bleeding with a platelet count of 85,000/µL, PT 18 sec (control 12 sec), aPTT 45 sec (control 32 sec), and fibrinogen 120 mg/dL. Which laboratory finding best distinguishes disseminated intravascular coagulation (DIC) secondary to placental abruption from consumptive coagulopathy due to massive transfusion?