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Clinical audit on association between platelet count and serological parameters in dengue fever cases in a tertiary care hospital
*Corresponding author: Tresa Remya Athipozhi Thomas, Department of Biochemistry, Sri Manakula Vinayagar Medical College and Hospital, Puducherry, India. tresa2812@gmail.com
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Received: ,
Accepted: ,
How to cite this article: Rajesh LM, Festus EL, Athipozhi Thomas T, Sweta K, Gopal M, Manavalan J, et al. Clinical audit on association between platelet count and serological parameters in dengue fever cases in a tertiary care hospital. Glob J Health Sci Res. 2025;3:98-105. doi: 10.25259/GJHSR_41_2025
Abstract
Objectives:
The study aimed to understand the prevalence of thrombocytopenia and the association between platelet count and serological parameters, NS1 Ag and IgM Ab, in clinically diagnosed dengue patients.
Material and Methods:
This is a hospital-based retrospective descriptive study. Data related to dengue patients were obtained from the Medical Records Department. Cases of 58 dengue patients registered for routine blood investigation for platelet count during November 2023–January 2024 were considered for the analyses. Data collected includes hospital ID, age, platelet count, NS1 Ag, and IgM Ab test results. Analysis of variance of platelet count and serological parameters were done to check age- and gender-wise variations. Pearson correlation analysis was performed to predict the outcome of the association of platelet count, NS1 Ag, and/or IgM Ab by linear regression, and P-values were calculated. The analyses were done using IBM Statistical Package for the Social Sciences statistics version 24.0.
Results:
Among 58 dengue cases, 60% were males and ~40% were females. The age of the individuals varied from 1 to 81 years with a mean age of 37 years. Platelet levels associated with dengue cases ranged from 10,000 to 290,000/mm3. Individuals within 18–60 years were the most affected group, where 10% of cases had a platelet count <20,000. Thrombocytopenia was prevalent in 79% of cases. Among all the dengue patients, 55% were positive for NS1 Ag and 48.3% for IgM Ab. Statistical analysis showed a significant variation in platelet count with age group, represented by a P < 0.05. However, there was not any considerable variation in platelet count with respect to gender. As per Pearson correlation analysis, a significant association was observed between platelet count and IgM Ab with a P value of 0.010. However, platelet count did not show considerable variation with NS1 Ag.
Conclusion:
The current study laid emphasis on thrombocytopenia as a prevalent clinical manifestation of dengue observed in ~79% of patients. Large fraction of thrombocytopenia cases underlines the severity of dengue cases and urges to adopt preventing strategies. Although NS1Ag is a reliable marker for early dengue detection, higher correlation of platelet level with IgM Ab signifies the mainstay diagnosis by antibody testing.
Keywords
Dengue virus
Immunoglobulin-M antibody
Non-structural 1 antigen
Platelets count
Thrombocytopenia
INTRODUCTION
Dengue is one of the most prevalent and rapidly spreading epidemic infections worldwide, and the reported cases have dramatically increased in the past two decades by 50–100 million/year.[1,2] It is a major mosquito-borne arboviral disease, and the severity and duration of the outbreak vary with the serotypes, genotypes, or lineages of the virus.[3] Dengue virus (DENV) belongs to the family Flaviviridae and genus Flavivirus. There are four serotypes of DENV, which causes human disease through transmission by mosquito vectors.[4] DENV infection results in a broad spectrum of clinical symptoms, ranging from mild fever to dengue hemorrhagic fever (DHF), the latter may progress to dengue shock syndrome and death.[5]
Thrombocytopenia is a common clinical manifestation of DENV infections in which blood platelet count decreases below the normal level of 150,000–450,000/mm3 and may fall under 40,000/mm3 in many cases.[6] The World Health Organization guidelines listed thrombocytopenia as an important clinical symptom of disease severity.[7,8] However, the pathogenesis of thrombocytopenia and bleeding in DENV infections is yet to be fully known. It could either arise from viral-induced decreased production of cells from the bone marrow or from increased destruction and clearance of platelets from peripheral blood.[9,10]
Thrombocytopenia could be associated with the positivity of the non-structural 1 antigen (NS1 Ag), a glycoprotein that plays a key role in the viability of the DENV and the only protein secreted into the bloodstream.[11,12] Due to its specificity and early presence in blood during illness, NS1 is considered an efficient marker of dengue diagnosis.[13] Another important and routinely used marker for dengue diagnosis is IgM Ab, which is captured through enzyme-linked immunosorbent assay.[14] Compared to early detection of antigen, the time span of the appearance of IgM Ab varies from 4 to 6 days.[15]
With a focus on deepening the understanding of thrombocytopenia in DENV infections, we proposed to study the platelet counts in dengue cases attending a tertiary care hospital. In addition, to assess the impact of the illness, associations of platelet levels with age, gender, and serological parameters, including NS1 Ag and IgM Ab, were also examined.
MATERIAL AND METHODS
Study design
A hospital-based retrospective descriptive study conducted over a 3-month period prospectively from November 1, 2023, to January 31, 2024 among dengue patients attending a tertiary care hospital.
Study setting and population
Data related to dengue patients were obtained from the Medical Records Department (MRD) of the tertiary care hospital. The study and related data analysis were carried out in the Central Research Laboratory. Patients registered for routine blood investigation for platelet count during November 2023–January 2024 were included in the study.
Sample size
Records of clinically diagnosed dengue cases from November 2023 to January 2024 in the tertiary care hospital were considered for the analysis. Data of 58 cases registered during the prescribed period are included in the study.
Data collection procedure
After obtaining consent from the authority, hospital IDs of dengue patients tested for platelet count and serological parameters during November 2023 to January 2024 were collected from the laboratory register of the tertiary care hospital. Based on the patient’s ID, parameters such as platelet count and test results of NS1 Ag and IgM Ab of each patient were retrieved from MRD.
Statistical analysis
Data obtained from MRD were represented as range, mean with standard deviation, or percentage as appropriate. Valid and cumulative percentages were calculated for positive results of NS1 Ag and IgM Ab. MS Excel was used to carry out an analysis of variance (ANOVA) in platelet count with age group and gender. Pearson correlation analysis was done to evaluate the extent of association between platelet count and serological parameters using IBM Statistical Package for the Social Sciences statistics version 24.0 (IBM Co., Armonk, NY, USA). A comprehensive flow chart of the study is depicted in Figure 1.
- Flow chart of the study. NS1 Ag: Non-structural 1 antigen (NS1 Ag), IgM Ab: Immunoglobulin-M antibody, ANOVA: Analysis of variance.
RESULTS
The study analyzed 58 cases with 60% males and ~40% females. The age of the individuals varied from 1 to 81 years with a mean of 37 years. The cases were divided into 3 age groups: ≤18 years, between 18 and 60, and ≥60 years. About 41 (~71%) of 58 cases were within 18–60 years, in which the number of male patients was nearly double (No: 27) that of females (No: 14). However, comparable proportion of both gender was observed below 18 years, and similar figures of both males and females were present above 60 years [Table 1].
| Age groups (years) | Gender | Total No. (%) | |
|---|---|---|---|
| No. of males (%) | No. of females (%) | ||
| ≥18 | 4 (6.9) | 5 (8.6) | 9 (15.5) |
| 18–60 | 27 (46.5) | 14 (24.1) | 41 (70.6) |
| ≥60 | 4 (6.9) | 4 (6.9) | 8 (13.7) |
| Total | 35 (60.3) | 23 (39.6) | 58 (100) |
Within 18–60 years, 10% of cases had intense thrombocytopenia (platelet counts <20,000/mm3). About 14% of individuals in this group had platelet count between 21,000 and 50,000/mm3, whereas 26% showed mild-to-moderate thrombocytopenia with counts between 51,000 and 100,000/mm3. Severe dengue cases were absent in patients under 18 and were limited to a few cases in 60 years and above. Overall, about 21% of dengue patients maintained normal platelet levels [Table 2].
| Age group (years) | Platelet count/mm3 No. of patients (%) |
||||
|---|---|---|---|---|---|
| <20,000 | 21,000–50,000 No. (%) |
51,000–1,00,000 No. (%) |
1,00,000–1,50,000 No. (%) |
>1,50,000 | |
| <18 | 0 | 0 | 5 (8.62) | 1 (1.72) | 3 (5.17) |
| 18–60 | 6 (10.34) | 8 (13.79) | 15 (25.86) | 8 (13.79) | 4 (6.90) |
| >60 | 1 (1.72) | 1 (1.72) | 0 | 1 (1.72) | 5 (8.62) |
| Total | 7 (12.06) | 9 (15.51) | 20 (34.48) | 10 (17.23) | 12 (20.69) |
<1,50,000 indicates thrombocytopenia cases
Gender-wise analysis of platelet count showed relatively higher values in females, varying from 17 × 103/mm3 to 296 × 103/mm3with an average of 106.47 × 103/mm3. In males, the counts were between 10 × 103/mm3 and 227 × 103/mm3 with an average of 83 × 103/mm3 [Figure 2]. Approximately 79% of dengue cases showed thrombocytopenia while 21% maintained normal platelet levels. Among these, the male population had a higher percentage of thrombocytopenia with 53.4% than females with ~23% [Figure 3].
- Gender-wise distribution of platelet count.
- Spread of thrombocytopenia in dengue patients.
Among dengue patients, 55% were positive for NS1 Ag, and 44.8% were non-reactive for the same. For IgM Ab, 48.3% were positive and 51.7% were non-reactive [Figure 4]. In essence, percentage of NS1 Ag positivity was higher than IgM Ab reactivity. A distinct age-wise variation in NS1 Ag and IgM Ab positivity was observed in the study. Maximum number of cases positive for both Ag and Ab were observed within 18 to 60 years constituting 21% and 39.7% respectively. Below 18 years and 60 years and above, both Ag and Ab positivity was relatively low among dengue patients. NS1 Ag was detected only in 1.7% of cases below 18 years. Lowest IgM response of 3.4% was observed among patients of 60 years and above [Figure 5].
- Percentage of non-structural 1 antigen (NS1 Ag) and immunoglobulin-M antibody (IgM Ab) positivity.
- Age-wise variation in non-structural 1 antigen and immunoglobulin-M antibody (IgM Ab).
Gender-wise variation was also noticeable in NS1 Ag and IgM Ab response in dengue patients. Large number of males were positive for both NS1 Ag and IgM Ab, with ~33% and 29%, respectively. Females showed 22% of NS1 Ag and 14% of IgM Ab response. About 7% females and a relatively large proportion of males constituting ~19% remain positive for both Ag and Ab [Figure 6]. Of the 58 dengue cases studied, thrombocytopenia was present in 46 cases. About 21.7% of thrombocytopenia cases were positive for NS1 Ag and ~24% for IgM Ab. Relatively large percentage (30.4%) of such cases were positive for both NS1 Ag and IgM Ab. Conversely, another 24% did not turn positive for either Ag or Ab [Figure 7]. The average platelet count of NS1 Ag positive and negative cases was similar represented by 92.44 × 103/mm3 and 92.69 × 103/mm3, respectively. However, large standard deviation (SD) shows a wide spread of values. However, mean platelet count of IgM Ab-positive cases showed a higher number of 99.96 × 103/mm3 than negative cases. Nevertheless, in both cases, the data values exhibited wide variation [Figure 8].
- Gender-wise variation in non-structural 1 antigen (NS1 Ag) and immunoglobulin-M antibody (IgM Ab) positivity.
- Spread of non-structural 1 antigen (NS1 Ag) and immunoglobulin-M antibody (IgM Ab) detection in thrombocytopenia cases.
- Distribution of platelet count in non-structural 1 antigen (NS1 Ag) and immunoglobulin-M antibody (IgM Ab)-positive and negative cases.
ANOVA of platelet count of three different age groups showed significant variation with a P < 0.05 [Table 3]. However, there was not any considerable variation in platelet count with respect to gender. As per Pearson correlation analysis, a significant association was observed between platelet count and IgM Ab with a P = 0.010. Nonetheless, antigenic data did not show a strong relationship with platelet count [Table 4].
| Summary | ||||||
| Groups | Count | Sum | Average | Variance | ||
| <18 | 9 | 1023 | 113.6667 | 4130.5 | ||
| 18–60 | 41 | 3225 | 78.65854 | 3362.18 | ||
| >60 | 8 | 1120 | 140 | 6012.857 | ||
| ANOVA | ||||||
| Source of variation | SS | df | MS | F | P-value | F crit |
| Between groups | 29937.13 | 2 | 14968.56 | 3.927422 | 0.025448 | 3.164993 |
| Within groups | 209621.2 | 55 | 3811.295 | |||
| Total | 239558.3 | 57 | ||||
ANOVA: Analysis of variance, SS: Sum of squares, DF: Degrees of freedom, MS: Mean squares, F: F-statistic
| NS1 Ag | Platelet count | IgM Ab | |
|---|---|---|---|
| NS1 Ag | |||
| Pearson correlation | 1 | −0.002 | −0.031 |
| Sig. (two-tailed) | 0.988 | 0.817 | |
| N | 58 | 58 | 58 |
| IgM Ab | |||
| Pearson correlation | −0.031 | −0.334* | 1 |
| Sig. (two-tailed) | 0.817 | 0.010 | |
| N | 58 | 58 | 58 |
DISCUSSION
As exposure to viral infection and response could vary with gender and age, it is important to examine the basic parameters related to dengue through age groups and genders. Among 58 dengue patients included in the study, about 60% were males and 40% females [Table 1]. Large percentages of male population affected by dengue were also reported by several studies, particularly in Asia.[16] It could be explained by more exposure of male population to dengue vector as they are assumed to be engaged in more outdoor activities than women.[17,18] An observational study conducted at a tertiary care center, Kerala, had male population of 56% compared to 41% females and the patients were in the age group of 25–44 years.[19] To an extent, relatable trend is also observed in the present study where ~71% of dengue patients belonged to the adult population of 18–60 years [Table 1].
This trend may vary with region as shown by a cross-sectional study in Faisalabad, Pakistan, where highest prevalence of dengue was diagnosed between relatively younger age of 16– 30 years.[17] Conversely, in North and South America, dengue cases reported are either an equal proportion of both male and female or large proportion of females.[20-22]
Platelet levels in dengue cases and thrombocytopenia
Platelet’s count varied from 10,000 to 2,90,000/mm3 where both lowest and highest counts were seen in the age group of 18–60 years [Table 2]. A median value of 75,000 was calculated from the platelet counts. An observational study from Kerala, India, also reported platelets in the range of 9,000–2,81,000 with a median value of 60,000/mm3.[19] In the present study, thrombocytopenia where platelets drop below 1,50,000/mm3 was detected in 79% cases. This is indeed a large figure compared to 30% of thrombocytopenia reported by Kulkarni et al. among suspected dengue fever (DF) cases in a tertiary care hospital.[23] DF with normal platelet count was observed in 33% of cases by a study conducted in Islamabad involving 250 dengue patients.[24] The present study, however, could see ~21% dengue cases with normal platelet levels [Figure 3]. Khan et al. also mentioned that only 2%[24] of the cases were categorized under severe thrombocytopenia compared to our study with 12% such cases. Although thrombocytopenia is commonly associated with DF, its severity could be a symptom of DHF.[25]
Decrease in platelet count, a characteristic feature of dengue was more evident in male patients than females with values ranging from 10,000 to 2,27,000 with a mean value of 83,000 [Figure 2]. A retrospective study conducted at a dengue serosurveillance center of a tertiary care hospital in Delhi, India, reported that the incidence of thrombocytopenia was significantly associated with females.[26] On the contrary, in this study, thrombocytopenia was associated with 53% of males and only 26% females [Figure 3].
Reactivity of NS1 Ag and IgM Ab in dengue patients
NS1 Ag positivity is reliable to address early dengue infection even when other serological tests are negative and often considered as a clinical feature of higher risk of progression into severe dengue.[27,28] About 55% of dengue cases in this study showed positive results for NS1 Ag. A study led by a tertiary care hospital and medical college, India, during 2014–2015 documented 33.3% NS1 positivity in serum samples from 358 suspected DF cases.[29] Several other studies from central and North India also listed 16–30% NS1 positivity in dengue cases.[23,30,31]
Like NS1 Ag, IgM Ab specific to dengue is a good indicator of infection and highly sensitive in the subsequent stages of infection.[23,32] About 48.3% positivity of IgM Ab is seen in the present study, which is lower than the antigen positivity. Since the antibody plays a pivotal role in the pathogenesis of DF, NS1 Ag along with IgM Ab serves as highly sensitive and reliable markers of dengue infection. The combination of these two markers proved to have the highest sensitivity of 97.8%.[23,32] In this study, age-wise variation in NS1 and IgM positivity was observed and the most notable difference was seen among 60 year and above where more number of cases confirmed NS1 Ag than IgM Ab [Figure 5]. Similar observations were also made by a study at Maternal and Child Tertiary health care, Rajasthan, where NS1 positivity was more prominent in patients below 10 years and was double than that of IgM Ab.[33] Considering the gender-wise variation in dengue biomarkers, males showed higher positivity than females with 33% and 29% for NS1 Ag and IgM Ab, respectively [Figure 6]. An observational cross-sectional study in a tertiary care hospital in Uttar Pradesh also concluded that number of males positive for NS1 Ag and IgM Ab was higher than that of female given by the ratio 1.54:1.[34]
Prevalence of thrombocytopenia in dengue cases
The present study shows a higher percentage (79%) of thrombocytopenia in dengue cases compared to some of the earlier studies from various tertiary care hospitals in India where prevalence range was 30–69%.[23,33] We observed a platelet count of <1,50,000 denoting thrombocytopenia in an alarming fraction of 64% within the population of 18–60 years [Table 2]. About 53.4% of thrombocytopenia cases were detected in males [Figure 3]. A retrospective study on dengue epidemic in Sao Paulo, Brazil, also stated age and gender as risk factors of thrombocytopenia. Men and older patients >65 years were three times more susceptible than the young population.[35] Nonetheless, in our study, percentage of thrombocytopenia in 60 and above was only 5% [Table 2]. About 30% of thrombocytopenia cases showed positivity toward NS1 Ag and IgM Ab and the cases showing the presence of either NS1 Ag or IgM Ab were 21.7 and 23.9%, respectively [Figure 7]. Related pattern was also noticed by a study conducted among clinically suspected DF cases in Guntur, Andhra Pradesh, where a greater number of thrombocytopenia cases were associated with IgM positivity than NS1 Ag.[36]
Relation of platelet count with age and serology
This study showed a significant variation in platelet level among different age groups (P < 0.05) [Table 3]. Such variations were also noted in dengue epidemic cases in Brazil where a strong correlation was evident with thrombocytopenia and patients within 46–64 years.[35] In contrast, an observational study carried out at a tertiary care hospital in Karnataka, India, could not find any association of platelet level with age in severe thrombocytopenia.[37] The present study also showed a strong correlation of platelet count to IgM Ab with a P value of 0.01 [Table 4]. This aligns with a study conducted in the western region of India where a higher degree of statistically significant association (P = 0.03) was found between thrombocytopenia and IgM.[38] However, there was not any considerable correlation between NS1 Ag and platelet levels in the current study, indicating NS1 Ag levels may not directly reflect the platelet depletion. Almost equal average platelet count of 92.4 × 103/mm3 and 92.6 × 103/mm3 was noted in NS1 Ag positive and negative cases, respectively [Figure 8].
One of the studies in a tertiary care hospital at Colombo, Sri Lanka, observed an association of NS1 Ag positivity and low platelet count, though not significant.[27] A strong association (P < 0.01) of thrombocytopenia with both NS1 Ag and IgM Ab positivity was observed among dengue cases in India at a tertiary care hospital.[23] Although the present study observed 30% of thrombocytopenia cases having both NS1 Ag and IgM Ab positivity [Figure 7], they did not show any significant association.
Limitations of the study
The study would benefit by incorporating hematological profile, clinical features of the patients, and analyzing their interrelatedness. Inclusion of platelet parameters such as mean platelet volume, platelet distribution width, plateletcrit, and platelet index would be helpful to assess the degree of thrombocytopenia in dengue patients.
CONCLUSION
Platelet levels among dengue cases varied from 10,000 to 290,000/mm3. Thrombocytopenia, a hallmark feature of dengue, was observed in 79% of the cases, highlighting its prevalence and clinical importance. Within 18–60 years, 10% of patients experienced severe thrombocytopenia, defined by platelet counts below 20,000/mm3. Significant association between platelet counts and IgM Ab suggests that antibody reactivity could serve as an indicator of disease severity, particularly in thrombocytopenia. These findings highlight that the multifaceted nature of dengue pathophysiology and emphasize the need for a comprehensive approach to select diagnostic markers based on the phase of illness. Monitoring IgM Ab levels alongside platelet counts may provide valuable insights into disease progression and severity, aiding in better clinical management of dengue patients.
Acknowledgment:
The authors acknowledge the MRD of the tertiary care hospital for providing data for retrospective analyses. The authors are also grateful to Ms. Shalini Balamurugan and Ms. Jasmine Manna Rani for their assistance during the study.
Ethical approval:
Institutional Review Board approval is not required as this is a retrospective study.
Declaration of patient consent:
Patient’s consent not required as patient identity was not disclosed or compromised.
Conflicts of interest:
There are no conflicts of interest.
Use of artificial intelligence (AI)-assisted technology for manuscript preparation:
The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.
Financial support and sponsorship: Nil.
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