In disseminated intravascular coagulation (DIC), which of the following laboratory findings is MOST specific for consumption of clotting factors?

Explanation

## Laboratory Diagnosis of DIC **Key Point:** DIC is characterized by **simultaneous activation of coagulation AND fibrinolysis**, resulting in consumption of platelets, fibrinogen, and clotting factors, with secondary elevation of fibrin degradation products (D-dimer, FDP). ### DIC Laboratory Profile | Test | Early DIC | Overt DIC | Interpretation | | --- | --- | --- | --- | | **Platelet count** | ↓ (mild) | ↓↓ (< 50,000) | Consumption | | **Fibrinogen** | Normal/↓ | ↓ (< 100 mg/dL) | Consumption + dilution | | **PT** | Normal/↑ | ↑ | Factor consumption | | **aPTT** | Normal/↑ | ↑ | Factor consumption | | **D-dimer / FDP** | ↑ | ↑↑ | Fibrinolysis | | **Thrombin time** | Normal/↑ | ↑ | Low fibrinogen + FDP | **Mnemonic:** **"FLAT"** — **F**ibrinogen ↓, **L**ow platelets, **A**bnormal PT/aPTT, **T**hrombotic microangiopathy ### Why Option 1 (Prolonged PT/aPTT + Low Fibrinogen + Elevated D-dimer) is Most Specific This constellation reflects: 1. **Consumption of clotting factors** (PT, aPTT prolonged) 2. **Consumption of fibrinogen** (low fibrinogen) 3. **Activation of fibrinolysis** (elevated D-dimer/FDP) Together, these three findings are **pathognomonic for DIC** and distinguish it from isolated fibrinolysis or factor deficiency. **High-Yield:** The **ISTH DIC Score** (International Society on Thrombosis and Haemostasis) uses: - Platelet count - D-dimer/FDP elevation - PT prolongation - Fibrinogen level A score ≥ 5 is compatible with overt DIC in the appropriate clinical context. **Clinical Pearl:** In DIC, **fibrinogen is consumed faster than it can be synthesized**, even though the liver is producing it. This is why fibrinogen drops despite hepatic production. In contrast, in liver disease alone, fibrinogen may be low but D-dimer is not markedly elevated (no active fibrinolysis). [cite:Harrison 21e Ch 181]