Dengue is one of the most rapidly spreading mosquito-borne viral infections worldwide, caused by the dengue virus belonging to the Flaviviridae family. It poses a significant public health burden in tropical and subtropical regions, including India. Clinical manifestations range from mild febrile illness to severe dengue characterized by plasma leakage, hemorrhage, and organ impairment. Thrombocytopenia is a hallmark of dengue infection, attributed to bone marrow suppression, peripheral destruction, and immune-mediated mechanisms. While platelet count is routinely used for monitoring, it may not fully reflect platelet function or activation status. Platelet indices such as mean platelet volume (MPV), platelet distribution width (PDW), and plateletcrit (PCT) are readily available from automated hematology analyzers and may provide additional insights into platelet kinetics and activation. These parameters have been increasingly studied as potential markers for disease severity. The present study aims to evaluate the role of platelet indices in dengue infection and correlate these indices with disease severity.

Study Design and Setting A cross-sectional observational study conducted in a tertiary care hospital over one year. Study Population • Total sample size: 180 patients • Inclusion: Laboratory-confirmed dengue (NS1 antigen or IgM ELISA positive) • Exclusion: Patients with hematological disorders, chronic liver disease, or other causes of thrombocytopenia Data Collection Detailed clinical and laboratory data were recorded. Classification of Dengue (WHO) • Dengue without warning signs • Dengue with warning signs • Severe dengue Laboratory Parameters • Platelet count • Mean Platelet Volume (MPV) • Platelet Distribution Width (PDW) • Plateletcrit (PCT) Statistical Analysis • Software: SPSS v25 • Tests: ANOVA, Pearson correlation • p < 0.05 considered significant

A total of 180 patients with laboratory-confirmed dengue infection were included in the present study. The demographic profile revealed a mean age of 32.6 ± 13 years, indicating that the majority of patients belonged to the young and middle-aged adult population, which is typically more exposed to mosquito-borne infections in endemic regions. A male predominance was observed, with males constituting 60% of the study population, while females accounted for 40%. This gender distribution may reflect greater outdoor exposure among males or differences in healthcare-seeking behavior. Based on the World Health Organization (WHO) classification, the study population was stratified into three categories according to disease severity. Dengue without warning signs constituted 50% of the cases, representing the largest group. Dengue with warning signs accounted for 35% of patients, while severe dengue was observed in 15% of cases. This distribution highlights that although the majority of cases are uncomplicated, a significant proportion progress to more severe forms, emphasizing the need for early identification and monitoring. The evaluation of platelet indices demonstrated marked variations across the severity spectrum. The mean platelet count showed a progressive decline with increasing disease severity. Patients with dengue without warning signs had a mean platelet count of 140 ± 35 ×10⁹/L, which decreased to 90 ± 25 ×10⁹/L in those with warning signs and further dropped to 45 ± 15 ×10⁹/L in severe dengue cases. This trend clearly indicates worsening thrombocytopenia with increasing severity and is consistent with the known pathophysiological mechanisms of dengue infection. In contrast, mean platelet volume (MPV) showed a rising trend with disease severity. The mean MPV was 8.5 ± 1.1 fL in patients without warning signs, increased to 9.8 ± 1.3 fL in those with warning signs, and reached 11.2 ± 1.5 fL in severe dengue cases. This increase in MPV suggests enhanced platelet turnover and release of larger, immature platelets from the bone marrow in response to peripheral destruction. Similarly, platelet distribution width (PDW), which reflects variability in platelet size, also demonstrated a significant increase across severity groups. The mean PDW was 13.5 ± 2.2% in dengue without warning signs, rising to 15.8 ± 2.5% in dengue with warning signs, and further increasing to 18.6 ± 3.1% in severe dengue. The elevated PDW values indicate increased platelet heterogeneity and activation, which are associated with inflammatory and pathological processes in dengue infection. Plateletcrit (PCT), which represents the total platelet mass in circulation, showed a decreasing trend with increasing severity. The mean PCT was 0.18 ± 0.05% in patients without warning signs, reduced to 0.12 ± 0.04% in those with warning signs, and further declined to 0.06 ± 0.02% in severe dengue cases. This reduction reflects the combined effect of decreased platelet count and altered platelet volume, indicating a significant decline in circulating platelet biomass. Statistical analysis revealed that the differences in platelet indices across the three severity groups were highly significant (p < 0.001), confirming a strong association between these parameters and disease severity. Correlation analysis further supported these findings. Platelet count demonstrated a negative correlation with disease severity, indicating that lower platelet counts are associated with more severe forms of dengue. In contrast, MPV showed a significant positive correlation with severity (r = +0.61, p < 0.001), suggesting that higher MPV values are indicative of severe disease. Similarly, PDW exhibited a positive correlation (r = +0.55, p < 0.01), reinforcing its role as a marker of platelet activation and disease progression. On the other hand, PCT showed a negative correlation with severity, reflecting reduced platelet mass in more advanced stages of the disease. Overall, the results clearly demonstrate that platelet indices vary significantly with dengue severity and may serve as valuable adjunct markers for assessing disease progression. Table 1: Comparison of Platelet Indices Across Different Severity Categories of Dengue Infection (Mean ± SD) Parameter Without Warning With Warning Severe Dengue Platelet count (×10⁹/L) 140 ± 35 90 ± 25 45 ± 15 MPV (fL) 8.5 ± 1.1 9.8 ± 1.3 11.2 ± 1.5 PDW (%) 13.5 ± 2.2 15.8 ± 2.5 18.6 ± 3.1 PCT (%) 0.18 ± 0.05 0.12 ± 0.04 0.06 ± 0.02 A statistically significant difference was observed across severity groups (p < 0.001). Correlation Analysis • Platelet count vs severity: negative correlation • MPV vs severity: positive correlation (r = +0.61, p < 0.001) • PDW vs severity: positive correlation (r = +0.55, p < 0.01) • PCT vs severity: negative correlation

The present study demonstrates a significant association between platelet indices and the severity of dengue infection, underscoring the clinical utility of these readily available hematological parameters. A progressive decline in platelet count was observed with increasing disease severity, which is consistent with the established pathophysiology of dengue. Thrombocytopenia in dengue is multifactorial, resulting from bone marrow suppression, immune-mediated peripheral destruction, and increased platelet consumption. The degree of thrombocytopenia often correlates with disease severity and risk of complications such as bleeding and plasma leakage. In addition to platelet count, the study highlights the importance of platelet indices in reflecting underlying pathophysiological changes. Mean platelet volume (MPV), a marker of platelet size and activity, was found to be significantly elevated in patients with severe dengue. Larger platelets are metabolically and enzymatically more active, indicating increased platelet turnover. This rise in MPV may represent a compensatory response of the bone marrow to peripheral platelet destruction, leading to the release of younger and larger platelets into circulation. Similar observations have been reported in previous studies, reinforcing the role of MPV as a potential indicator of disease severity. Platelet distribution width (PDW), which reflects variability in platelet size, was also significantly increased in severe dengue cases. Elevated PDW indicates greater heterogeneity in platelet morphology, often associated with platelet activation and anisocytosis. In the context of dengue infection, this may be attributed to both increased platelet destruction and the release of immature platelets. Furthermore, elevated PDW has been linked with inflammatory and thrombotic conditions, suggesting that it may also reflect the systemic inflammatory response seen in severe dengue. The parallel increase in both MPV and PDW supports the concept of enhanced platelet activation and turnover during disease progression. Plateletcrit (PCT), representing the total platelet mass in circulation, showed a declining trend with increasing severity of dengue. This reduction is primarily due to the marked decrease in platelet count and reflects diminished platelet biomass. Since PCT provides a more comprehensive assessment of platelet status by integrating both platelet count and volume, its decrease further emphasizes the extent of hematological compromise in severe cases. The combined evaluation of platelet count and platelet indices provides a more nuanced understanding of platelet dynamics in dengue infection. While platelet count alone is a commonly used marker, it may not fully capture the functional and morphological changes occurring during the disease. Platelet indices, being part of routine complete blood count analysis, offer additional information without incurring extra cost or requiring specialized investigations. The findings of the present study suggest that platelet indices can serve as useful adjunct markers for early identification of severe dengue cases. In resource-limited settings, where access to advanced diagnostic tools may be restricted, these parameters can aid in timely risk stratification and clinical decision-making. Early recognition of patients at risk of severe disease can facilitate closer monitoring, prompt intervention, and improved outcomes. Overall, the study reinforces the importance of integrating platelet indices into routine clinical assessment of dengue patients. Their simplicity, accessibility, and diagnostic relevance make them valuable tools in enhancing the management of dengue infection, particularly in endemic regions. LIMITATIONS • Single-center study • Moderate sample size • Lack of follow-up data • No viral serotyping

The present study demonstrates that platelet indices, particularly mean platelet volume (MPV) and platelet distribution width (PDW), show a significant correlation with the severity of dengue infection. An increase in MPV and PDW, along with a decline in platelet count and plateletcrit, reflects enhanced platelet activation and disease progression. These parameters, which are routinely available through automated hematology analyzers, can serve as simple, rapid, and cost-effective tools for early risk stratification. Incorporating platelet indices into routine evaluation may aid clinicians in timely identification of severe cases and improve patient monitoring and management, especially in resource-limited healthcare settings.

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