Role of Hematological and Immunological Parameters in COVID-19 Patients.

BACKGROUND: The ongoing pandemic of coronavirus disease 2019 (COVID-19) which was caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to efforts from the medical and scientific community in understanding the biological basis of COVID-19 pathophysiological mechanisms. Thus, analysis of various hematological and immunological parameters may be helpful for COVID-19 infection evaluation for risks involved and effectiveness in management. AIM: The aim of this study was to analyze the role of various hematological and immunological parameters in patients infected with SARS-CoV-2.
MATERIALS AND METHODS: This retrospective analysis was performed on 300 patients who tested positive for SARS-CoV-2 by quantitative reverse transcription-polymerase chain reaction analysis. All participants of the study were divided into - (a) Group I: patients with mild symptoms and normal chest radiographic findings; (b) patients with moderate disease presenting with fever and cough along with other respiratory symptoms, and (c) patients suffering from severe disease. Data collection was done from all patients at the time of hospital admission for hematological and immunological parameters - (a) total leukocyte count, (b) lymphocyte count, (c) lymphocytic subset count, (d) lactate dehydrogenase (LDH) levels, (e) D-dimer, (f) C-reactive protein (CRP), and (g) ferritin levels. SPSS 22.0 software was used for determining P values by independent t-test and Chi-square test.
RESULTS: The median age was 65 years (interquartile range -57-71 years). While comparing white blood cell and lymphocyte counts, extremely significant P values were obtained. D-dimers and ferritin levels demonstrated extremely significant P values while both LDH and CRPs showed statistical significance. Correlation of lymphocytic subsets showed extreme significance in total lymphocyte counts in mild-to-moderate as compared to severely infected patients while both CD4+ and CD8+ counts demonstrated statistical significance in mild-moderate infected cases. Statistical significance was noted in D-dimer, CRP, and LDH levels also.
CONCLUSION: Assessment of hematological and immunological parameters can be used to plan the management of COVID-19 patients. Copyright:

INTRODUCTION

The erstwhile ongoing viral pandemic, coronavirus disease 2019 (COVID-19), was first of all reported from Wuhan which is located in Hubei province of China as cases of pneumonia of unknown etiology. In the early days of January 2020, this virus was identified from a patient using the next-generation sequencing method from the Chinese Center for Disease Control and Prevention. This disease was formally named the “severe acute respiratory syndrome coronavirus 2” (SARS-CoV-2) which was renamed as COVID-19 by the World Health Organization.[1] The SARS-CoV-2 has been named as such due to its similarity to a disease outbreak caused by SARS-CoV.[2] The SARS-CoV-2 belongs to β-coronavirus genus of family of coronavirus. This branch of coronavirus relates to the SARS-CoV and Middle East respiratory syndrome-related coronavirus (MERS-CoV). The SARS-CoV-2 demonstrates 79% genetic homology while the MERS-CoV shows 51.8% homology. The main routes of transmission of SARS-CoV-2 are respiratory droplets and transmission through surface contact.[3] It is a single-stranded RNA virus. It enters inside a host cell through human angiotensin-converting enzyme-2 and effects the numerous immunological mechanisms existing within the human body beginning at the time of viral entry and its replication within the body. The host response includes an increase in hematopoiesis, an increase in myeloid cell population which includes neutrophils and monocytes, and production of a multitude of cytokines along with chemokines. However, in case regulatory mechanisms that control these bodily phenomena do not occur, then the tissue damage and cytokine storm manifesting as dysfunction of organs come into existence.[4]

This disease is characterized by a broad plethora of a variety of signs and symptoms which are found to have numerous manifestations such as pyrexia, cough, dyspnea, pneumonia, and fatigue due to involvement of multiple organ systems such as nervous, gastrointestinal, and cardiovascular systems. Laboratory investigations have demonstrated high levels of serum ferritin, C-reactive protein (CRP), lactate dehydrogenase (LDH), and low white blood cell counts accompanied with lymphopenia.[56] It has been suggested that the virus, SARS-CoV-2 protein, infects hemoglobin protein by causing immunological hemolysis in red blood cells.[7]

Epidemiological analysis has demonstrated that the SARS-CoV-2 has higher contagious potential when compared to SARS-CoV and MERS-CoV although it has shown lesser fatality compared to these previous epidemics.[89] COVID-19-positive patients are categorized into four groups depending on their clinical manifestations such as (a) light, (b) common, (c) severe, and (d) critical. A study revealing the postmortem biopsy of a COVID-19-infected patient revealed a drastic decrease in numbers of hyperactivated CD4+ and CD8+ T-lymphocytes.[10] The platelet-to-lymphocytic ratio is an inflammation-related biomarker which reflects the severity of systemic inflammation and cytokine storm.[111213]

Patients diagnosed with COVID-19 infection may demonstrate mild-to-severe symptoms related to an acute infection of inflammatory origin. Those suffering from mild disease exhibit symptoms such as dry cough, fatigue, fever, and abnormalities in computed tomography scan of the chest. Few patients worsen rapidly which can turn the disease into acute respiratory distress syndrome (ARDS) which may culminate in multiple organ failure in short time period. According to various published reports, the mortality from COVID-19 ranges from 2.3% to 15%.[14151617]

Thus, it has been proposed that immunological factors play an important role in rapid disease progression. Hence, studying these immunological factors is important for early-stage identification of severe cases of COVID-19. Based on the above findings, the aim of the study was to analyze the role played by various hematological and immunological parameters in COVID-19 patients.

MATERIALS AND METHODS

This was a retrospective study analysis performed on 300 patients who demonstrated positivity toward SARS-CoV-2 by utilizing the quantitative reverse transcription–polymerase chain reaction. Study participants were divided into the following groups – (a) Group I: patients presenting with mild symptoms and normal chest radiographic findings; (b) patients with moderate disease presenting with symptoms such as fever and cough along with other respiratory symptoms; and (c) patients suffering from severe disease exhibiting – (a) respiratory distress which was defined as “respiratory rate which is more than 30 breaths per minute,” (b) <93% oxygen saturation, and (c) ≤300 mmHg of oxygenation index.

Data were collected from all patients at the time of hospital admission for assessing the hematological and immunological findings – (a) (a) total leukocyte count, (b) lymphocyte count, (c) lymphocytic subset count, (d) LDH levels, (e) D-dimer, (f) CRP, and (g) ferritin levels. Statistical analysis was performed using the IBM, Armonk, NY, USA, statistical software. Independent t-test and Chi-square test were used to determine P values.

Ethics approval

This study was conducted in compliance with the protocol; ethical approval was obtained from the institutional ethical committee (EE/024-9920).

RESULTS

Of all the 300 COVID-19 patients, the median age was found to be 65 years (interquartile range: 57–71 years, range = 29–85 years). There were 152 mild symptomatic cases, 55 moderate symptomatic patients, while 93 belonged to severe category. All hematological and immunological parameters were noted [Table 1].

Table 1

Demonstrating hematological and immunological parameters in coronavirus disease 2019-positive patients

Parameters	P
WBC count (cells/mm3)	0.0001
Lymphocytic count (%)	0.0001
LDH (U/L)	0.002
D-dimer (ng/ml)	0.0003
CRP (mg/dl)	0.002
Ferritin (ng/ml)	0.0002

WBC: White blood cell, LDH: Lactate dehydrogenase, CRP: C-reactive protein

On comparing, the white blood cell count (cells/mm3) and lymphocyte count (percentage) extremely significant (P = 0.0001) were obtained. Immunological marker assessments of D-dimers (ng/ml) and ferritin levels are demonstrated extremely significant statistical P value (P = 0.0003 and 0.0002, respectively) while both levels of LDH (U/L) and CRPs (mg//dl) demonstrated significant P = 0.002, each [Table 1 and Graph 1].

Graph 1

Graph demonstrating P values for various parameters

On correlating various lymphocytic subsets, the following data were obtained on statistical correlation [Table 2]:

Table 2

Correlation between various subsets of lymphocytes

Lymphocyte subsets	Mild to moderate cases		Severe cases
	Rs.	P	Rs.	P
Total T-lymphocytes	0.3	0.04	0.17	0.5
CD4 + T-cells	0.25	0.05	0.35	0.2
CD8 + T-cells	0.28	0.06	0.12	0.67
NK-cells	0.35	0.8	0.12	0.64
B-lymphocytes	0.2	0.15	0.47	0.06
CD4+/CD8+ ratio	0.017	0.87	0.06	0.85

Total T-lymphocyte counts – In mild-to-moderate cases, an extremely significant difference of P = 0.04 was obtained, while in severe cases, no statistical significance (P = 0.5) could be derived [Table 2]

CD4+ lymphocytic count – Again, a statistically significant difference (P = 0.05) was obtained in CD4+ T-lymphocytic counts in mild-to-moderate cases of COVID-19, while in severe cases, no statistical significance was observed (P = 0.2) [Table 2]

CD8+ T-lymphocytic count – Here also, a statistically significant P value (0.06) was obtained while no statistical significance was obtained in severe cases (P = 0.67) [Table 2]

Natural killer (NK) cell counts – No statistically significant differences were observed in both mild-to-moderate symptomatic (P = 0.8) and severe COVID-19 cases (P = 0.64) [Table 2]

B-lymphocyte count – The B-lymphocytic count demonstrated statistical significance (P = 0.06) in severe cases, while in mild-to-moderate COVID-19 cases, no statistical significance was obtained (P = 0.15) [Table 2]

CD4+/CD8+ lymphocytic T-cell count ratio – No statistical significance was observed in the CD4+/CD8+ ratios in both mild-to-moderate and severe cases of COVID-19 infections [Table 2].

DISCUSSION

Various longitudinal studies across the globe on immune system responses can help in identifying biomarkers for immune effectiveness and thus may help in tackling this global infectious disease. Furthermore, research directed toward the immune responsiveness, thus enabling to devise a disease-specific treatment.[9]

The novel scope of this research included the investigation of various laboratory parameters that were associated with the severity and mortality of COVID-19 infection. These parameters including white blood cell (WBC) count; lymphocytes, platelet count, D-dimer, and ferritin were screened and evaluated in patients during the progression of this pandemic. The estimation of other inflammatory biomarkers such as CRP estimated the severity of disease.

In the current study, on comparing various hematological and immunological parameters, both the white blood cells and lymphocyte counts demonstrated extremely significant P values (0.0001, each). Immunological biomarker assessment comprising D-dimer and ferritin levels also showed extremely significant P values (0.0003 and 0.0002, respectively). Furthermore, both LDH and CRP levels showed statistical significance (P = 0.002, each). On comparing various lymphocytic subsets, B-lymphocyte counts showed statistical significance in severe COVID-19 symptomatic cases with no significance in mild to moderately symptomatic cases. An extremely statistical significant difference was noted in total lymphocytic counts in mild to moderately infected cases of COVID-19. Both the CD4+ and CD8+ lymphocytic counts demonstrated statistical significance in mild-to-moderate cases whereas no statistical significance was noted in NK cells’ counts. Our findings have been supported and confirmed by numerous investigators who have reported their findings from across the world as mentioned below.

Ding et al. analyzed the vital hematological parameter profile of COVID-19-infected patients during their hospital stay. 54.2% and 27.8% of the patients were shown to suffer from lymphopenia and leukopenia, respectively. 20.8% of the patients were of severe presentation while 79.2% were nonsevere in nature. In the nonsevere cases, higher counts of leukocytes, neutrophils, and lymphocyte-to-neutrophil ratio were seen. The lymphocytic counts were found to reduce in severe cases. In addition, a positive correlation of lymphocyte-to-neutrophil count was seen during the hospital stay. However, it was also noted that there were no hematological events occurring at simultaneous period of time. Thus, an immunological system disturbance which includes cytokine storm, lymphopenia, and imbalance in lymphocytic subgroups has been found to occur in COVID-19-infected patients and its severity may be closely linked with the extent of hematological disturbances.[1]

Ma et al. in their investigation compared various clinical manifestations and immunological profiles of COVID-19 patients undergoing hemodialysis with those with only COVID-19 infection. Analysis of blood samples using flow cytometry showed that various populations of lymphocytes had undergone a significant reduction. Furthermore, COVID-19 patients on hemodialysis had displayed a remarkable decrease in serum inflammation-causing cytokines.[5]

Najim and Kadhim in their study compared the levels of various laboratory parameters such as serum ferritin, CRP, D-dimer, and LDH levels. They also showed that COVID-19-infected patients had lower white blood cell counts which exhibited lymphopenia. Most of the study participants showed significantly high serum lactate dehydrogenase levels and serum CRPs. High levels of these acute-phase reactant markers have been related. They demonstrated lower lymphocytic percentage (P = 0.0001) and significant rise in serum ferritin, CRP, D-dimer, and LDH levels (P = 0.0001, 0.001, 0.0002, and 0.0004, respectively). All of these are acute-phase reactant markers which when elevated are associated with poor prognosis in COVID-19-infected patients.[6]

Zhao et al. in their study reported that the frequency of CD4+ T-cells has been positively correlated with lymphocytic counts (r = 0.787) and oxygen saturation levels (r = 0.295) while the CD4+ T-cells have a negative correlation with age (r = 0.323) and neutrophilic counts (r = −0.244). P < 0.001 was obtained on comparing the immunological parameters of nonsurvivors of COVID-19 disease.[8]

Wang et al. also reported depletion of lymphocytes along with platelets in COVID-positive patients.[10] Tan et al. have reported that lymphopenia may be used as an indicator for detecting the severity of COVID-19, and thus, it acts as an adjunctive aid for identifying prognostic indicators for differentiating between early and severe cases of COVID-19.[11]

Liao et al. reported thrombocytopenia (platelet count <100 × 109 cells//liter) in critical state patients. Both the lymphocytic and eosinophilic counts were reduced in patients with critical disease compared to those with moderate or severe disease (P < 0.0001). The prothrombin time, degradation of fibrin, and D-dimers were found to significantly increase with increasing severity of the disease (P < 0.0001). Using the multivariate analysis, it was seen that there was a significant association of mortality with thrombocytopenia (P = 0.00045), prolonged prothrombin time (P = 0.0094), an increase in neutrophil-to-lymphocytic ratio (P = 0.0042), and an increase in D-dimer (P = 0.041). In addition, thrombotic complications include ischemia of extremities, stroke, and venous thromboembolism. A reduction in platelet counts (thrombocytopenia) was observed. Furthermore, extremely significant P values (<0.001) were found on comparing the prothrombin time, fibrin degradation products, and D-dimers in critical compared to those with moderate and severe disease.[12]

Zhang et al. in their investigation reported that the lymphocytic subsets were closely linked with severity and progression of COVID-19 disease. While in patients diagnosed with nonsevere COVID-19, recovery in overall T-cell count was observed on a day-to-day basis following the onset of the disease. In the end, it was surmised that CD4+ and CD8+ T-lymphocytic count served as predictors of risk for assessing the outcome for COVID-19. It has been suggested that acquired immunological host response is important for effective clearance of virus from the body. It has been reported that following infection by SARS-CoV-2, the CD4+ T-lymphocyte cells undergo rapid activation into T-helper cells which are pathogenetic in nature. Following this activation, the pathogenetic Th1 lymphocytes get activated and cause secretion of cytokines which are pro-inflammatory in nature, namely interleukin-6 (IL-6). This IL-6 activates monocytic cells which after entering the pulmonary circulation results in serious injury to the lungs. Thus, it has been suggested that by blocking the IL-6 or granulocyte-monocyte colony-stimulating factor, an inhibition of immunopathological injury can be undertaken.[18]

Yuan et al. studied 117 laboratory-confirmed SARS-Co-V-2-infected patients and found that the severely affected and critically sick patients had low lymphocytic count (P < 0.01); decreased red blood cell counts and levels of hemoglobin (P < 0.01), low immunoglobulin G (IgG) levels (P < 0.05) and significantly high levels of D-dimer (P < 0.0001), fibrinogen (P < 0.01), counts of white blood cells (P < 0.01) and neutrophilic count (P < 0.0001), IL-6 levels (P < 0.05), CRP levels (P < 0.01), level of procalcitonin (P < 0.01), and erythrocyte sedimentation rate (ESR) (P < 0.05), Significant ferritin levels (P < 0.01) along with LDH (P < 0.01) levels.[2] These authors confirmed the impaired counts of red blood cells, lymphocytes, and IgG antibodies in COVID-19-infected patients. In addition, blood was found to be in a hypercoagulable state in patients who were critically sick.[2]

Mathew et al. analyzed 125 COVID-19-hospitalized patients. They reported that although the CD4 and CD8+ lymphocytic cells were activated in some individuals, there was a limited T-cell response in others. In few patients, it was observed that the proliferation of CD4+ and CD8+ T-cells is consistent with antiviral response while the plasmablastic response was seen in more than 30% of B-lymphocytes. Thus, different immunotypic patterns were seen in the COVID-19 patients who were hospitalized.[19]

Zhu et al. in their analysis on 127 confirmed COVID-19 patients who were hospitalized and grouped into (a) severe and b) nonsevere groups found that high CRPs and IL-6 levels along with hypertension are risk factors that are independent in assessment of the severity of COVID-I9 affliction.[20]

Mann et al. in their study found no significant difference in neutrophil, lymphocytic, monocytic, and total white blood cell counts between mild, moderate, and severe cases of COVID-19. Although, a progressively higher neutrophil-to-lymphocytic count was seen among these patients.[4] Thus, there exists a greatly elevated neutrophilia in severe cases of COVID-19 which contributes to the ARDS.[2122]

Various neutrophilic by-products have been found in sera of patients suffering from COVID-19 and can be strongly correlated with biochemical parameters such as LDH, D-dimer, and CRP levels.[23] In fact, analysis of cohorts presenting with elevated WBC levels (odds ratio [OR] = 1.75), neutrophilic count (OR = 2.62), D-dimers (OR = 3.97), a prolonged prothrombin time (OR = 1.82), elevated fibrinogen levels (OR = 3.14), increased ESR (OR = 1.60), levels of procalcitonin (OR = 4.76), IL-6 (OR = 2.10), and IL-10 (OR = 4.93) has demonstrated higher OR of progressing to severe disease phenotype.[2425]

CONCLUSION

COVID-19 is a disease which is not limited within the boundaries of its country of origin, however, it has spread all across the world in a brief span of time. As a result of this, emerging research from all corners of the world is providing wide information and a variety of clinical data of patients infected with COVID-19 virus that might help in the early detection in various patient categories along with helping in characterizing the associated complications specifically, in association with other chronic diseases. However, there are insufficient data that can characterize varied changes in the hematological and immunological parameters in the COVID-19-infected patients. This study has provided with additional findings which can help in developing management protocols in various stages of COVID-19-infected patients.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.