Which of the following is the characteristic feature that distinguishes dengue hemorrhagic fever (DHF) from dengue fever (DF)?

Explanation

## Dengue Hemorrhagic Fever: Diagnostic Criteria **Key Point:** DHF is defined by the WHO as dengue with hemorrhagic manifestations PLUS evidence of plasma leakage (hemoconcentration, pleural effusion, ascites) AND thrombocytopenia (platelet count <100,000/μL). ### Classification of Dengue Severity | Feature | Dengue Fever (DF) | Dengue Hemorrhagic Fever (DHF) | |---------|-------------------|--------------------------------| | **Hemorrhagic signs** | Absent or mild | Present (petechiae, ecchymosis, GI bleed) | | **Platelet count** | Normal or mildly reduced | <100,000/μL | | **Hemoconcentration** | Absent | Present (Hct rise ≥20%) | | **Plasma leakage** | None | Evidence on imaging or clinical signs | | **Shock** | No | May progress to DSS | **High-Yield:** The critical distinction is NOT just hemorrhage, but hemorrhage + thrombocytopenia + plasma leakage (hemoconcentration). This triad defines DHF and separates it from uncomplicated DF with minor bleeding. **Clinical Pearl:** A patient with dengue who develops a rising hematocrit (>20% above baseline) despite falling platelet count is showing plasma leakage—the hallmark of DHF and a warning sign for progression to dengue shock syndrome (DSS). ### Pathophysiology of Plasma Leakage Dengue virus infection of endothelial cells triggers: 1. Increased vascular permeability via cytokine release (TNF-α, IL-6, IL-8) 2. Complement activation and immune complex deposition 3. Platelet dysfunction and consumption 4. Net result: fluid extravasation into interstitial space → hemoconcentration **Warning:** Fever duration and rash characteristics are common to both DF and DHF; they do NOT distinguish between them. Serological markers (IgM/IgG) appear similarly in both forms.