A dengue patient develops dengue haemorrhagic fever (DHF) Grade III. Which haematological finding BEST distinguishes DHF from dengue fever?

• A Platelet count <100,000/µL
• B Leucopenia with lymphocytosis
• C Elevated NS1 antigen
• D Haematocrit rise ≥20% above baseline ✓

Explanation

The WHO classification of DHF requires ALL four criteria: fever, haemorrhagic manifestations, thrombocytopenia (<100,000/µL), and evidence of plasma leakage — specifically a haematocrit rise ≥20% from baseline or equivalent drop after fluid replacement. Plasma leakage (not merely thrombocytopenia) is the pathophysiological hallmark differentiating DHF from dengue fever. DHF Grade III/IV (dengue shock syndrome) adds circulatory failure. Leucopenia and NS1 antigen are diagnostic of dengue infection but not specific to DHF. The haematocrit rise ≥20% is the single most important distinguishing criterion.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.