D-dimer levels are negative while FDP is positive. This pattern helps distinguish primary fibrinogenolysis from DIC. Which option reflects that distinction?

• A. Elevated D-dimer
• B. Positive FDP
• C. Negative D-dimer
• D. Schistocytes present

Answer: (C)

D-dimer is produced when cross-linked fibrin is degraded by plasmin, so its presence signals breakdown of cross-linked fibrin formed during coagulation. In primary fibrinogenolysis (fibrinolysis without significant coagulation), plasmin mainly degrades fibrinogen and non–cross-linked fibrin, leading to elevated fibrinogen degradation products (FDP) but little or no cross-linked fibrin to form and break down, so D-dimer stays negative. In contrast, DIC involves widespread coagulation with formation of cross-linked fibrin, and its subsequent breakdown releases D-dimer; FDP can be elevated in both conditions, but the D-dimer rise points to cross-linked fibrin degradation. Thus, a pattern of FDP positive with D-dimer negative best indicates primary fibrinogenolysis rather than DIC. Elevated D-dimer would favor DIC, a positive FDP alone is less specific, and schistocytes reflect microangiopathic processes but don’t define this specific pattern.