A 5-year-old girl from Mumbai presents with fever for 6 days, severe abdominal pain, vomiting, and a platelet count of 45,000/μL. NS1 antigen is negative. IgM antibody against dengue is positive. She is suspected to have dengue hemorrhagic fever. Which investigation is most appropriate to assess the severity and guide fluid management?

## Severity Assessment in Dengue Hemorrhagic Fever (DHF) **Key Point:** Hematocrit (packed cell volume) is the single most important investigation for assessing plasma leakage and guiding fluid resuscitation in DHF. A rise in hematocrit ≥20% from baseline indicates significant plasma leakage. ### Role of Hematocrit in DHF Classification **High-Yield:** Hematocrit is used to: 1. **Diagnose plasma leakage** — a hallmark of DHF (rise ≥20% from baseline or ≥40% in absolute value) 2. **Assess severity** — guides the need for fluid resuscitation 3. **Monitor response to therapy** — serial measurements show adequacy of fluid management 4. **Predict progression** — rising hematocrit despite fluid therapy suggests ongoing plasma leakage and risk of shock ### Investigations in Dengue Hemorrhagic Fever | Investigation | Purpose | Timing | Clinical Significance | |---|---|---|---| | **Hematocrit (PCV)** | Plasma leakage assessment | **Serial, every 6–12 hrs** | **Rise ≥20% = DHF; guides fluid therapy** | | **Platelet count** | Thrombocytopenia severity | Daily | <100,000 = DHF; <50,000 = severe | | **Coagulation profile** | Bleeding risk | If bleeding manifestations | Prolonged PT/aPTT in severe cases | | **LFTs & albumin** | Liver involvement, nutritional status | Baseline | Hypoalbuminemia in plasma leakage | | **D-dimer/FDP** | DIC screening | If coagulopathy suspected | Not routine; expensive | **Clinical Pearl:** In DHF, the **hematocrit-to-platelet ratio** is a useful bedside marker. A rising hematocrit with falling platelets is pathognomonic for dengue hemorrhagic fever and indicates the need for aggressive fluid resuscitation. ### Fluid Management Algorithm Based on Hematocrit ```mermaid flowchart TD A[Suspected DHF]:::outcome --> B[Baseline hematocrit]:::action B --> C{Hematocrit rise?}:::decision C -->|<10%| D[Oral rehydration, monitor]:::action C -->|10-20%| E[IV fluids: Ringer's lactate 5-10 mL/kg/hr]:::action C -->|>20% or rising| F[IV fluids: 10-20 mL/kg/hr, ICU monitoring]:::urgent F --> G[Serial hematocrit every 6 hrs]:::action G --> H{Hematocrit stable?}:::decision H -->|Yes| I[Reduce fluid rate]:::action H -->|No, rising| J[Increase fluids, consider transfusion]:::urgent ``` **Mnemonic:** **HEMATOCRIT** — **H**igh PCV = plasma leakage; **E**very 6 hrs serial; **M**anage fluids accordingly; **A**ssess severity; **T**rend matters more than absolute value; **O**ver-resuscitation risks pulmonary edema; **C**ritical in DHF; **R**ise ≥20% = danger; **I**ntensive monitoring; **T**herapy guided by serial values