In disseminated intravascular coagulation, which of the following laboratory findings is MOST specific for active fibrinolysis and distinguishes DIC from other causes of thrombocytopenia?

Explanation

## Laboratory Diagnosis of DIC: The Consumptive Coagulopathy Pattern **Key Point:** DIC is characterized by simultaneous **consumption of clotting factors and platelets** coupled with **secondary fibrinolysis**. The combination of low fibrinogen, elevated FDP, and prolonged PT/aPTT is pathognomonic. ### The DIC Laboratory Triad | Finding | Mechanism | Why It Occurs | |---------|-----------|---------------| | **Low fibrinogen** | Consumption by thrombin | Widespread fibrin formation depletes fibrinogen | | **Elevated FDP** | Secondary fibrinolysis | Plasmin degrades deposited fibrin | | **Prolonged PT/aPTT** | Factor consumption | Factors II, V, VII, VIII, X, XIII consumed | | **Thrombocytopenia** | Platelet consumption | Incorporated into microthrombi | | **Elevated D-dimer** | Fibrin breakdown | Highly sensitive but NOT specific | **High-Yield:** The **combination** of low fibrinogen + elevated FDP + prolonged PT/aPTT + thrombocytopenia = DIC. No single test is diagnostic; you need the pattern. ### Why Each Finding Matters 1. **Fibrinogen** — decreases progressively as it is consumed 2. **FDP (fibrin degradation products)** — rises due to secondary fibrinolysis (plasmin degrades fibrin clots) 3. **PT/aPTT** — prolonged because clotting factors are consumed 4. **Platelets** — fall due to incorporation into microthrombi **Clinical Pearl:** In **chronic DIC** (e.g., malignancy), fibrinogen may be normal or elevated because the liver compensates with increased synthesis. In **acute DIC** (sepsis, trauma), fibrinogen drops rapidly. ### DIC Scoring System (ISTH) DIC diagnosis requires: - Platelet count < 100 × 10⁹/L - D-dimer/FDP elevated - PT prolonged - Fibrinogen < 100 mg/dL A score ≥ 5 is compatible with overt DIC.