## Distinguishing Dengue Fever from Dengue Hemorrhagic Fever ### Key Clinical Discriminator **Key Point:** The hallmark of dengue hemorrhagic fever (DHF) is the **triad of thrombocytopenia (<100,000/μL), hemoconcentration (elevated hematocrit ≥20%), and plasma leakage** — these features are absent in uncomplicated dengue fever (DF). ### Comparative Features | Feature | Dengue Fever (DF) | Dengue Hemorrhagic Fever (DHF) | |---------|-------------------|--------------------------------| | **Platelet count** | Normal to mildly decreased | <100,000/μL (critical finding) | | **Hematocrit** | Normal | Elevated ≥20% (plasma leakage) | | **Hemorrhagic manifestations** | Absent or minor petechiae | Positive tourniquet test, spontaneous bleeding | | **Plasma leakage** | Absent | Present (pleural effusion, ascites) | | **Shock** | Does not occur | May occur (dengue shock syndrome) | | **Myalgia/arthralgia** | Present in both | Present in both | | **Fever pattern** | Present in both | Present in both | | **NS1 antigen** | Positive in both | Positive in both | ### High-Yield Classification **High-Yield:** WHO 2009 classification defines DHF by: 1. Fever (any duration) 2. Hemorrhagic manifestations (positive tourniquet test, petechiae, ecchymosis, bleeding from GI tract, gum, injection sites) 3. Thrombocytopenia (<100,000/μL) 4. Evidence of plasma leakage (hemoconcentration, pleural effusion, ascites, hypoproteinemia) **Clinical Pearl:** The **critical phase** (days 3–7) is when plasma leakage peaks and DHF becomes apparent. Platelet count dropping below 100,000/μL combined with rising hematocrit is the biochemical signature of DHF. ### Why Other Features Are Non-Discriminatory - **Myalgia and arthralgia** occur in both DF and DHF - **Biphasic fever** is typical of DF but can also occur in DHF - **NS1 antigen positivity** is present in both DF and DHF (viremia phase) [cite:Park 26e Ch 20]
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