## Distinguishing Dengue Fever from Dengue Hemorrhagic Fever ### Key Discriminating Feature **Key Point:** Plasma leakage (evidenced by rising hematocrit, pleural effusion, ascites, or hypoproteinemia) combined with thrombocytopenia (<100,000/μL) is the cardinal feature that separates DHF from uncomplicated dengue fever. This represents the critical pathophysiologic transition from vasculitis to increased vascular permeability. ### Comparative Table: Dengue Fever vs DHF | Feature | Dengue Fever | DHF Grade I | DHF Grade II+ | | --- | --- | --- | --- | | **Platelet count** | Often normal or mild ↓ | <100,000/μL | <100,000/μL | | **Plasma leakage** | Absent | Present (mild) | Present (moderate–severe) | | **Hematocrit rise** | <20% | ≥20% | ≥20% | | **Bleeding manifestations** | Absent or mild | Spontaneous bleeding or positive tourniquet test | Spontaneous bleeding | | **Shock** | Absent | Absent | May occur (DSS) | ### Why Other Features Are Non-Discriminatory **High-Yield:** Myalgia, arthralgia, and biphasic fever occur in uncomplicated dengue and are NOT specific to DHF. NS1 antigen positivity is seen in both dengue fever and DHF during the acute phase and does not distinguish severity. ### Clinical Pearl The **critical window** for DHF recognition is day 3–5 when fever subsides but plasma leakage peaks. Platelet count drop + hematocrit rise during defervescence = DHF until proven otherwise. This is when fluid resuscitation becomes life-saving. [cite:Park 26e Ch 7]
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