From the Research
Hematocrit rises in dengue fever primarily due to plasma leakage, which is a hallmark of severe dengue infection, as evidenced by the most recent study in 2025 1.
Background
Dengue infection triggers an immune response that increases vascular permeability, allowing plasma to leak out of blood vessels into surrounding tissues and body cavities. As plasma volume decreases while red blood cell mass remains constant, the proportion of red blood cells in the total blood volume (hematocrit) increases.
Pathophysiology
This plasma leakage occurs due to the release of inflammatory cytokines and other mediators that damage the endothelial cells lining blood vessels, as supported by a study in 2022 2. The World Health Organization considers a rapid rise in hematocrit (20% or more from baseline) accompanied by a decreasing platelet count as an important warning sign of progression to severe dengue.
Clinical Implications
Clinicians monitor hematocrit levels closely in dengue patients as rising values indicate worsening plasma leakage and potential progression to dengue shock syndrome, which requires immediate fluid resuscitation, as noted in a study from 2007 3. The hematocrit typically begins to rise during the critical phase of illness, around days 3-7 of fever, when defervescence (fever reduction) occurs.
Key Findings
A recent study in 2025 1 identified early circulating biomarkers, including Vascular cell adhesion molecule-1 and Interleukin 33 receptor, to predict plasma leakage in dengue fever. These biomarkers could improve clinical assessment and patient care in dengue cases. Another study in 2018 4 highlighted the importance of ultrasonography in detecting plasma leakage in dengue patients.
Recommendations
Monitoring hematocrit levels and using ultrasonography to detect plasma leakage are crucial in managing dengue patients, as they can help identify patients at risk of severe outcomes and guide timely interventions 1, 4.