Which combination of findings would support a diagnosis of primary fibrinogenolysis?

• A. Fibrinogen decreased; FDP positive
• B. Fibrinogen increased; FDP negative
• C. Fibrinogen decreased; D-dimer positive
• D. Fibrinogen normal; FDP negative

Answer: (A)

In primary fibrinogenolysis, plasmin directly degrades fibrinogen, causing a drop in fibrinogen levels while producing fibrinogen degradation products (FDP). Because no cross-linked fibrin is formed, D-dimer, which comes specifically from breakdown of cross-linked fibrin, may not be elevated. So the pattern you’d expect is low fibrinogen with positive FDP (indicating fibrinogen breakdown by plasmin).

That’s why the finding of decreased fibrinogen with positive FDP best supports primary fibrinogenolysis. The other patterns don’t fit: an increased fibrinogen level isn’t compatible with consumption by fibrinolysis; decreased fibrinogen with a positive D-dimer would suggest fibrin formation and cross-linking (as in DIC or thrombolysis), not isolated fibrinogenolysis; and a normal fibrinogen with negative FDP shows no fibrinogen degradation activity.