Evaluation of Haematological Parameters in Dengue Fever: A Hospital-Based Study

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1. Introduction

Dengue fever is an acute mosquito-borne viral illness caused by the dengue virus (DENV-1 to DENV-4), transmitted primarily by Aedes aegypti and Aedes albopictus. It is among the most rapidly spreading arboviral diseases worldwide, with an estimated 100–400 million infections each year, the majority occurring in tropical and subtropical regions including the Indian subcontinent [1,2]. The clinical spectrum ranges from a self-limiting febrile illness to severe forms characterised by plasma leakage, haemorrhage and shock [3].

Haematological alterations are a hallmark of dengue infection and frequently precede overt clinical deterioration. Thrombocytopenia, leukopenia, haemoconcentration and atypical lymphocytosis reflect the underlying pathophysiology of bone-marrow suppression, immune-mediated platelet destruction and increased vascular permeability [4,5]. Because these changes can be detected early through a simple complete blood count, haematological monitoring serves as an accessible and inexpensive tool for assessing disease progression in resource-limited settings [6].

Despite the availability of serological confirmation through NS1 antigen and IgM/IgG antibody testing, the complete blood count remains indispensable for day-to-day management and triage [7]. The present hospital-based study was therefore undertaken to evaluate the pattern of haematological parameters in confirmed dengue patients and to examine their association with clinical warning signs, with the aim of supporting early risk stratification.

2. Methodology

• Study design and setting: This was a hospital-based descriptive observational study conducted in the Department of Pathology of a tertiary-care teaching hospital over a six-month period (July to December 2025), coinciding with the post-monsoon dengue transmission season. • Study population: A total of 180 patients of either sex with serologically confirmed dengue infection were included. Confirmation was based on a positive NS1 antigen test and/or dengue-specific IgM antibody by ELISA. Patients with other concurrent febrile illnesses (malaria, enteric fever, sepsis), pre-existing haematological disorders, chronic liver disease or those on anticoagulant/antiplatelet therapy were excluded to avoid confounding. • Data collection: Demographic details, day of illness at presentation and clinical findings were recorded using a structured proforma. Venous blood samples collected in EDTA vacutainers were analysed on a five-part automated haematology analyser. Parameters studied included haemoglobin, haematocrit, total leukocyte count, differential count and platelet count. • Thrombocytopenia was defined as a platelet count <150 ×10³/µL and graded as mild (100–150), moderate (50– 99) or severe (<50). Leukopenia was defined as a total leukocyte count <4.0 ×10³/µL. Warning signs were identified according to the WHO 2009 classification. • Statistical analysis: Data were compiled in a spreadsheet and analysed using standard statistical software. Continuous variables were expressed as mean ± standard deviation and categorical variables as frequencies and percentages. The chi-square test was used to assess associations between haematological abnormalities and warning signs; a p-value <0.05 was considered statistically significant. Institutional ethics committee approval and informed consent were obtained.

3. Results

Of the 180 confirmed dengue patients, 110 (61.1%) were male and 70 (38.9%) were female, giving a male-to-female ratio of 1.57:1. The mean age was 28.6 ± 13.2 years, with the largest proportion in the 21–30-year age group. NS1 antigen was positive in 124 (68.9%) patients and dengue IgM in 92 (51.1%). Baseline characteristics are summarised in Table 1.

Table 1: Demographic and baseline characteristics of the study population (n = 180). Characteristic Value Mean age (years) 28.6 ± 13.2 Male, n (%) 110 (61.1)

Mean day of illness at presentation 4.3 ± 1.6 The mean values of the major haematological parameters and the frequency of their derangements are presented in Table 2. Thrombocytopenia was the most common abnormality, observed in 141 (78.3%) patients, followed by leukopenia in 86 (47.8%) and atypical lymphocytes in 68 (37.8%). A raised haematocrit suggestive of haemoconcentration was noted in 54 (30.0%) patients.

Table 2: Mean haematological parameters and frequency of abnormalities. Parameter Mean ± SD Abnormality (n, %)

Fig 1: Frequency of haematological abnormalities among dengue patients (%).

Among the 141 patients with thrombocytopenia, moderate thrombocytopenia was the most frequent grade (43.3%), while severe thrombocytopenia (<50 ×10³/µL) was present in 36 (25.5%) patients. The distribution of severity grades and association with warning signs is shown in Table 3. Severe thrombocytopenia and raised haematocrit were both significantly associated with the presence of warning signs (p < 0.05).

Serial platelet counts by day of illness showed a progressive decline reaching a nadir around the sixth day, followed by spontaneous recovery during convalescence, as illustrated in Figure 2. This pattern underscores the importance of timing when interpreting a single platelet value.

Fig 2: Mean platelet count by day of illness showing the characteristic nadir and recovery.

4. Discussion

The present study confirms that haematological derangements are a consistent and clinically meaningful feature of dengue infection. The male predominance (61.1%) and the clustering of cases in the second and third decades of life are in keeping with previous Indian reports, likely reflecting greater outdoor exposure among young adult males rather than any true biological susceptibility [8,9]. Thrombocytopenia emerged as the most frequent abnormality, affecting 78.3% of patients, a finding consistent with the wide range of 60–90% reported across the literature [10,11]. The pathogenesis is multifactorial, involving direct viral suppression of megakaryopoiesis, immune-mediated peripheral destruction of platelets and platelet sequestration [12]. Importantly, the characteristic fall in platelet count to a nadir around the sixth day of illness, followed by recovery, highlights that a single low value must be interpreted in the context of the day of illness rather than in isolation [13]. Leukopenia (47.8%) and atypical lymphocytosis (37.8%) reflect the marrow-suppressive and immune-activating effects of the virus and may point to the diagnosis even before serological confirmation [5,6]. The significant association of raised haematocrit and severe thrombocytopenia with warning signs reinforces the role of haemoconcentration as a marker of plasma leakage and impending severe disease [3,14]. Being simple and rapidly available, these parameters are particularly valuable for triage in resource-limited settings. The strength of this study lies in its reliance on routinely available, low-cost investigations that are easily replicated in peripheral hospitals. Its limitations include a single-centre design, modest sample size and the absence of serial day-wise sampling for every patient. Larger multicentric studies with serial monitoring and outcome correlation would further strengthen these observations [15].

5. Conclusion

Haematological parameters, particularly platelet count and haematocrit, are reliable, inexpensive and widely accessible indicators of disease activity in dengue fever. Thrombocytopenia is the most common abnormality, while severe thrombocytopenia and haemoconcentration correlate with clinical warning signs. Serial monitoring of the complete blood count, interpreted in relation to the day of illness, enables early identification of patients at risk of progression and supports timely intervention, thereby contributing to reduced morbidity and mortality.