In severe dengue, which laboratory finding best characterises the critical 'plasma leakage' phase that increases risk of dengue shock syndrome (DSS)?

• A Dengue NS1 antigen positivity alone
• B Serum bilirubin > 2 mg/dL with AST elevation
• C Rising haematocrit ≥20% above baseline with thrombocytopaenia < 100,000/µL ✓
• D IgM seroconversion on dengue serology

Explanation

The critical phase of dengue (days 3–7) is characterised by plasma leakage from capillaries due to DENV-induced cytokine release and increased vascular permeability. WHO dengue warning signs include rising haematocrit (≥20% increase from baseline or above local population reference) — haemodilution in reverse — combined with rapid platelet drop (<100,000/µL). These parameters indicate fluid shifting into third space (pleural effusion, ascites) predicting DSS. NS1 antigen is an early diagnostic marker (not severity). IgM seroconversion indicates secondary or recent infection.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.