A 32-year-old woman presents to the emergency department with spontaneous bleeding from gums and multiple petechiae over her lower limbs for 3 days. She denies any recent trauma or drug intake. Vital signs are stable. Laboratory investigations reveal: Hemoglobin 10.2 g/dL, Platelet count 8,000/μL, PT 12 sec (control 12 sec), aPTT 32 sec (control 32 sec), Bleeding time 8 minutes (normal <5 min). Peripheral blood smear shows no abnormal cells. What is the most likely diagnosis?

Explanation

## Clinical Analysis **Key Point:** The patient presents with severe thrombocytopenia (8,000/μL) with spontaneous bleeding and normal coagulation times (PT and aPTT), indicating a platelet number/function defect rather than a coagulation cascade defect. ### Laboratory Interpretation | Finding | Patient Value | Interpretation | |---------|---------------|----------------| | Platelet count | 8,000/μL | Severe thrombocytopenia (normal: 150,000–400,000/μL) | | PT | 12 sec | Normal (extrinsic pathway intact) | | aPTT | 32 sec | Normal (intrinsic pathway intact) | | Bleeding time | 8 min | Prolonged (platelet dysfunction or low count) | | Hemoglobin | 10.2 g/dL | Mild anemia (likely from bleeding) | | Peripheral smear | No abnormal cells | Rules out leukemia, microangiopathy | ### Why This Is ITP **High-Yield:** ITP is characterized by: 1. **Isolated thrombocytopenia** — platelet count alone is low; RBC and WBC are normal 2. **Normal coagulation times** — PT and aPTT are normal because coagulation factors are intact 3. **Prolonged bleeding time** — reflects the severe reduction in platelet number 4. **Clinical presentation** — spontaneous bleeding (petechiae, gum bleeding) in the absence of systemic illness 5. **Immune-mediated destruction** — autoantibodies against platelet surface antigens (GPIIb/IIIa or GPIb/IX) cause clearance by splenic macrophages **Clinical Pearl:** Bleeding time is a poor screening test for coagulation disorders but is abnormal in thrombocytopenia (especially <50,000/μL) because platelet adhesion and aggregation are impaired. ### Pathophysiology of ITP ```mermaid flowchart TD A[Autoimmune attack on platelets]:::outcome --> B[IgG antibodies bind platelet surface]:::action B --> C[Splenic macrophages recognize IgG-coated platelets]:::action C --> D[Fc-receptor-mediated phagocytosis]:::action D --> E[Rapid platelet destruction]:::outcome E --> F[Severe thrombocytopenia]:::outcome F --> G{Platelet count <20,000/μL?}:::decision G -->|Yes| H[Spontaneous bleeding risk]:::urgent G -->|No| I[Bleeding with trauma only]:::outcome ``` **Mnemonic:** ITP = **I**solated **T**hrombocytopenia with **P**latelet destruction (immune-mediated) ### Why DIC, vWD, and Factor V Deficiency Are Wrong See **whyEachDistractorIsWrong** section below.