Which laboratory finding best distinguishes DIC (disseminated intravascular coagulation) from TTP (thrombotic thrombocytopenic purpura) in a critically ill patient presenting with thrombocytopenia and microangiopathic hemolytic anemia?

## Distinguishing DIC from TTP: Coagulation Profile ### Key Pathophysiologic Difference **Key Point:** DIC is a consumptive coagulopathy driven by widespread thrombin generation and fibrin deposition, whereas TTP is a primary thrombotic microangiopathy caused by ultra-large von Willebrand factor multimers. ### Comparison Table | Feature | DIC | TTP | |---------|-----|-----| | **PT/aPTT** | Prolonged | Normal or slightly prolonged | | **Fibrinogen** | Markedly decreased (<100 mg/dL) | Normal or mildly decreased | | **Platelet count** | Variable decrease | Severe (<20,000/μL typical) | | **D-dimer** | Markedly elevated | Mildly elevated | | **Schistocytes** | Present (mild to moderate) | Present (prominent) | | **LDH** | Elevated | Markedly elevated | | **Renal function** | May be abnormal | Often severely abnormal | | **Neurologic signs** | Absent | Present in 60% | ### High-Yield Discriminator **High-Yield:** The **coagulation cascade activation** in DIC consumes factors and fibrinogen, producing: - Prolonged PT and aPTT - Low fibrinogen (consumption) - Elevated D-dimer and FDPs In contrast, TTP has **intact coagulation studies** because the primary defect is platelet aggregation and mechanical hemolysis, not factor consumption. ### Clinical Pearl **Clinical Pearl:** A patient with thrombocytopenia + microangiopathic hemolysis + **normal PT/aPTT/fibrinogen** = think TTP first. A patient with the same findings + **prolonged PT/aPTT + low fibrinogen** = think DIC (often secondary to sepsis, trauma, or malignancy). ### Mnemonic **Mnemonic:** **DIC = Consumption Coagulopathy** (Decreased factors, Increased D-dimer, Consumed fibrinogen) **TTP = Thrombotic Microangiopathy** (Thrombocytopenia, Thrombosis, normal coagulation Tests)