Platelet count and hematocrit monitoring in dengue

What it measures

Serial CBC tracks the key warning signs of dengue: falling platelets and rising hematocrit (plasma leakage). Monitoring is usually daily or more often during the critical phase (days 3–7).

Specimen and preparation

• Specimen: EDTA whole blood
• Tube: Lavender top
• Preparation: Repeat every 12–24 h (more often if unstable); record baseline hematocrit early.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Hematocrit rise ≥ 20% from baseline: plasma leakage
• Hematocrit rise with rapid platelet fall: warning sign
• Persistently high hematocrit despite fluids: ongoing leakage

Causes of low values

• Platelets < 100 × 10⁹/L: typical of critical phase
• Platelets < 20 × 10⁹/L: bleeding risk
• Falling hematocrit with instability: suspect hemorrhage
• Leukopenia is common early

Method

Automated hematology analyser; manual PCV and smear platelet estimate

Good to know

Recovery is marked by rising platelets and WBC; always verify very low automated platelet counts on a smear.

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