## Distinguishing Dengue Fever from Dengue Hemorrhagic Fever ### Key Diagnostic Criterion **Key Point:** The hallmark discriminator between dengue fever (DF) and dengue hemorrhagic fever (DHF) is **plasma leakage**, evidenced by hemoconcentration (rising hematocrit ≥20% above baseline or ≥40% absolute), pleural effusion, or ascites. Thrombocytopenia alone is NOT sufficient to diagnose DHF. ### Clinical Features Comparison | Feature | Dengue Fever | Dengue Hemorrhagic Fever | |---------|--------------|-------------------------| | **Plasma leakage** | Absent | Present (defining feature) | | **Hemoconcentration** | Absent | Present (Hct rise ≥20%) | | **Platelet count** | Often <100,000 | <100,000 (common but not diagnostic) | | **Rash, myalgia, fever** | Present | Present | | **Hemorrhagic manifestations** | Minor (petechiae) | Spontaneous bleeding, GI bleed | ### Why Plasma Leakage is the Discriminator **High-Yield:** Dengue viremia causes endothelial dysfunction and increased vascular permeability during the **critical phase** (typically days 3–7). This plasma leakage is the pathophysiologic hallmark of DHF and distinguishes it from uncomplicated DF. **Clinical Pearl:** A child with fever, rash, and thrombocytopenia alone may still have DF if there is no evidence of plasma leakage. Conversely, a child with rising hematocrit, pleural effusion, or ascites has DHF regardless of bleeding manifestations. ### WHO Classification (2009) DHF requires: 1. Fever (recent or ongoing) 2. Hemorrhagic manifestations (positive tourniquet test, petechiae, ecchymosis, or spontaneous bleeding) 3. **Thrombocytopenia (<100,000/μL)** 4. **Evidence of plasma leakage** (hemoconcentration, pleural effusion, ascites, hypoproteinemia) **Mnemonic: PLASM** — **P**lasma leakage, **L**ow platelets, **A**cute hemorrhage, **S**evere vascular permeability, **M**ultiple organ involvement (DHF defining features). [cite:Park 26e Ch Dengue]
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