Prognosis of COVID-19: Red Cell Distribution Width, Platelet Distribution Width, and C-Reactive Protein

Introduction Cytokine storm is central in the pathobiology of Coronavirus disease 2019 (COVID-19). The pro-inflammatory state and hypoxia disrupt erythropoiesis leading to alterations in red cell distribution width (RDW) and hematocrit. Platelet production increases alongside its destruction, inviting newly formed immature platelets into the circulation. Thus, the platelet distribution width (PDW) and mean platelet volume (MPV) are also affected. The study's objective is to analyze these indices and C-reactive protein (CRP) to elucidate prognostic insights in COVID-19 patients at the time of admission. Methodology This study was a retrospective cross-sectional study conducted at Chigateri General Hospital, attached to JJM Medical College, Davangere, over two months, July and August of 2020. Patients falling under categories B and C according to the interim guidelines issued by the Ministry of Health and Family Welfare, Government of India were enrolled in this study. Patients requiring mechanical ventilation and those with a prior diagnosis of malignancy were excepted from the study. Results The study population comprised a total of hundred patients. Seventy-five patients survived the disease and were discharged; twenty-five patients succumbed to the viral illness. The mean age of survivors (43.0 +/- 13.6 years) was significantly lesser than that of non-survivors (59.1 +/- 11.5 years) (p <0.001). RDW was significantly different among survivors (p=0.002); PDW and CRP were lower among the deceased (p=0.05 and p=0.10, respectively). Cut off values for RDW as 15%, CRP as 67 mg/l, and PDW as 17% were significantly associated with mortality. Hematocrit and MPV were not significantly associated with mortality. RDW has a sensitivity of 92% and a negative predictive value of 95% in predicting mortality. Discussion RDW showed a significant association with increased mortality. Impaired cell-mediated immunity at the onset of infection is responsible for rapid progression to moderate or even severe COVID disease. Since the investigations in our study were ordered at the time of admission, it may lead us to believe that higher RDW is associated with a better patient outcome. Lower C-reactive protein levels are associated with higher mortality. CRP is a non-specific marker for inflammation. Raised CRP is customarily an indicator of acute inflammation. Notwithstanding, the raised CRP may be an indicator of baseline immune response in early COVID infection. High PDW shows a significant association with increased mortality. The pathobiology of change in platelet indices in COVID-19 patients is presumably multifactorial: infection of the bone marrow; autoimmune platelet destruction; platelet sequestration. Conclusion Red cell distribution width, platelet distribution width, and C-reactive protein are useful early predictive markers of mortality in COVID-19. Although serial investigations would provide a better picture, these indices at admission can gauge the clinical outcome early in the disease. As there is still a lot to be understood about the natural history of COVID-19, our study aims to propose relatively inexpensive indices of mortality that can aid efficient management.


Results
The study population comprised a total of hundred patients. Seventy-five patients survived the disease and were discharged; twenty-five patients succumbed to the viral illness. The mean age of survivors (43.0 +/-13.6 years) was significantly lesser than that of non-survivors (59.1 +/-11.5 years) (p <0.001). RDW was significantly different among survivors (p=0.002); PDW and CRP were lower among the deceased (p=0.05 and p=0.10, respectively). Cut off values for RDW as 15%, CRP as 67 mg/l, and PDW as 17% were significantly associated with mortality. Hematocrit and MPV were not significantly associated with mortality. RDW has a sensitivity of 92% and a negative predictive value of 95% in predicting mortality.

Discussion
RDW showed a significant association with increased mortality. Impaired cell-mediated immunity at the onset of infection is responsible for rapid progression to moderate or even severe COVID disease. Since the investigations in our study were ordered at the time of admission, it may lead us to believe that higher RDW is associated with a better patient outcome.
Lower C-reactive protein levels are associated with higher mortality. CRP is a non-specific marker for inflammation. Raised CRP is customarily an indicator of acute inflammation. Notwithstanding, the raised CRP may be an indicator of baseline immune response in early COVID infection.
High PDW shows a significant association with increased mortality. The pathobiology of change in platelet indices in COVID-19 patients is presumably multifactorial: infection of the bone marrow; autoimmune platelet destruction; platelet sequestration.

Conclusion
Red cell distribution width, platelet distribution width, and C-reactive protein are useful early predictive markers of mortality in COVID-19. Although serial investigations would provide a better picture, these indices at admission can gauge the clinical outcome early in the disease. As there is still a lot to be understood about the natural history of COVID-19, our study aims to propose relatively inexpensive indices of mortality that can aid efficient management.

Introduction
In December 2019, a new illness, caused by a novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), broke out in Wuhan city, China. In January 2020, the World Health Organization declared the outbreak a Public Health Emergency of International Concern [1].
Multifactorial causation is responsible for the relationship between mean platelet volume and Coronavirus disease 2019 (COVID-19). In a study conducted by Güçlü et al., there was an increase in mortality by 1.76 times for every one unit increase in mean platelet volume [2]. Bone marrow is infected, which leads to thrombocytopenia. There is a destruction of platelets by the immune system. Lastly, more platelets get consumed due to accumulation in the lungs. Platelet count decrease leads to an increase in platelet production. There is an increased production of young platelets, which are functionally more active than older platelets. All these factors lead to an increase in the mean platelet volume. Mean platelet volume can function as a simple, economical, quick, and widely available laboratory parameter that recognizes the severe presentation of COVID-19 [2].
Platelet distribution width (PDW) reflects the variation in the size of platelets. PDW increases when platelet destruction increases and there are variations in the size of newly formed immature platelets [3]. Increased cytokine release and inflammation lead to higher platelet production and increased platelet destruction. SARS-CoV-2 utilizes its spike protein to enter host cells by binding to angiotensin-converting enzyme 2 (ACE2) on the host cell membrane. Transmembrane protease serine 2, a serine protease, proteolytically cleaves and activates the spike protein to facilitate SARS-CoV-2 virus-cell membrane fusions. The spike protein potentiates thrombus formation. Coagulation factors are released, inflammatory cytokines are secreted, and leukocyte platelet aggregates are formed [4].
Red cell distribution width (RDW) conveys the degree of anisocytosis among red blood cells. Anisocytosis is a hugely inflammation dependent process. Many of the proinflammatory cytokines like TNF-α and interleukin-1 decrease erythropoietin production during cytokine storm. Additionally, hypoxia induces disruption of erythropoiesis in COVID-19. Super-added infections are quite common in COVID-19, therefore increasing sepsis. RDW plays a considerable role even in sepsis. Hematological analyzers automatically generate RDW and can hence be ordered multiple times per day [5]. Also, RDW can significantly predict mortality even after discharge from the intensive care unit [6].
The study's objective is to simultaneously assess and provide insights regarding several hematological indices in the mortality of COVID-19 patients at the time of admission.

Materials And Methods
This study was a retrospective cross-sectional study conducted at Chigateri General Hospital, attached to JJM Medical College, Davangere, over two months, July and August of 2020. Clearance was taken from the Institutional Ethics Committee to begin the study.
Patients with a confirmed diagnosis of SARS-COV-2 infection, positive real-time polymerase chain reaction (RT-PCR) for viral ribonucleic acid (RNA) were included in the study. Only patients falling under categories B and C according to the interim guidelines issued by the Ministry of Health and Family Welfare, Government of India were enrolled in this study [7]. Patients requiring mechanical ventilation and those with a prior diagnosis of malignancy were excepted from the study. Tocilizumab, pirfenidone, azathioprine, and cyclophosphamide were not administered to any of the patients. Figure 1 presents the treatment plan followed for all patients included in this study.
The laboratory records and clinical data of the patients were accessed and analyzed on IBM Statistical Package for the Social Sciences (SPSS) Statistics for Windows, version 27 (IBM Corp., Armonk, NY). Hematocrit (HCT), co-efficient of variation of the red cell distribution width (RDW-CV), C-reactive protein (CRP), co-efficient of variation of the platelet distribution width (PDW), and the mean platelet volume (MPV) were analyzed for their ability to predict and prognosticate the clinical outcome.
The demographic data has been depicted as descriptive statistics. The unpaired t-test was employed to compare the mean between two groups of data. Mann-Whitney U test was employed to compare the mean of two sets of non-parametric data. The chi-square test was used for categorical data. Odd's ratio was used to calculate the odds of occurrence of mortality using these indices. Diagnostic validity tests and receiver operator characteristic curves were applied to analyze and contrast the different indices. A p-value of 0.05 or less was deemed statistically significant.

Results
The study population comprised a total of 100 patients. Seventy-five patients survived the disease and were discharged; 25 patients succumbed to the viral illness. The study population's mean age was 47.1 ± 14.8 years, ranging from 20 years to 78 years. Of the 100 participants, 57 were males, and 43 were females.
The mean age of patients who survived the disease was 43 years, significantly lesser than that of nonsurvivors (59.1 years), with a p-value of <0.001 ( Table 1).    Table 3 presents the different indices in a comparison between survivors and non-survivors. RDW was significantly higher among the patients who survived the disease with a p-value of 0.002 as against the nonsurvivors. PDW and CRP were lower among the deceased, and the strength of the associations were p=0.05 and 0.10, respectively.  The unpaired t-test has been used in the analysis of data that followed a normal distribution (HCT, MPV, and PDW). RDW and CRP were analyzed using the Mann-Whitney U test.  The diagnostic validity of RDW, PDW, and CRP at the abovementioned cut-off values have been presented in Table 5. RDW has a sensitivity of 92% and a negative predictive value of 95% in predicting mortality. Figure  2 compares the diagnostic validity of RDW, PDW, and CRP in the prediction of mortality.

Discussion
RDW showed a significant association with increased mortality. With a cut-off value as 15 mg/dl, RDW of lower than 15% was significantly associated with increased mortality (X ²= 12.02, p = 0.001). RDW also has a high sensitivity of 92% and a high negative predictive value of 95% in predicting adverse outcomes. This observation disagrees with a study done by Foy et al., which found that RDW higher than 14.5% was associated with higher mortality [8]. Also, a study by Gong et al. ascertained a similar result. Uncontrolled immune activation in COVID-19 can result in increased red cell turnover, which can raise RDW. Various cytokines like IL-1 and TNF alpha can raise erythropoietin secretion, raising RDW [9]. Conversely, Sharma et al. concluded that there was no significant association between RDW and mortality [10]. This ambiguity shows that the relationship between RDW and mortality is not consistent, and further investigation into the same is warranted.
Impaired cell-mediated immunity at the onset of infection is responsible for rapid progression to moderate or even severe COVID disease. Since the investigations in our study were ordered at the time of admission, it may lead us to believe that higher RDW is associated with a better patient outcome. However, the modestly raised RDW is within normal limits and may indicate baseline immune response in early infection. The importance of robust cell-mediated immunity in preventing severe COVID has adequately been described in the literature [11].
Lower C-reactive protein levels are associated with higher mortality, but the association's significance was defined at smaller confidence intervals (p < 0.10). CRP lower than 67 mg/dl was associated with higher mortality (X² = 5.41, p = 0.02). CRP also has a high negative predictive value of 87% and a high sensitivity of 76%. In a study by Wang, the size of the pulmonary lesion and CRP levels showed a positive correlation [12]. Findings in our study were conflicting with this. CRP is a non-specific marker for inflammation. Raised CRP is customarily an indicator of acute inflammation [13]. Notwithstanding, the raised CRP may be an indicator of baseline immune response in early COVID infection. An appropriate brisk immune response in the early stages of infection could decrease viral load and, by extension, decrease illness severity. Since the patients included in the study were in the early stages of infection, presenting within four days of symptoms, low CRP could indicate a weak baseline immune response, thereby resulting in a worse clinical outcome [11].
High PDW shows a significant association with increased mortality. A cut-off value of 17% was significantly associated with increased mortality (X² = 6.31, p = 0.012). PDW also has a high sensitivity of 84% and a high negative predictive value of 89%. This finding concurs with Güçlü et al. and Yun et al. [2,14]. The pathobiology of change in platelet indices in COVID-19 patients is presumably multifactorial. The following three hypotheses related to platelet count and structure are proposed in COVID-19: 1. As with other coronaviruses, thrombocytopenia is perhaps due to infection of the bone marrow.
3. Platelet sequestration in the lungs in response to alveolar damage may be responsible for the altered finding.

Limitations
A limitation of this study is that financial and logistical constraints came in the way of conducting serial investigations. The size of the sample was small and, larger studies are necessary to validate the findings. Also, follow-up of patients after discharge could not be done.

Conclusions
Red cell distribution width, platelet distribution width, and C-reactive protein are useful, inexpensive, and early predictive markers of mortality in COVID-19. Although serial investigations would provide a better picture, these indices at admission can gauge the clinical outcome early in the disease. As there is still a lot to be understood about the natural history of COVID-19, our study aims to propose relatively inexpensive indices of mortality that can aid efficient management.