RDW, Platelet Kinetics and Survival Outcome in Covid-19 Hospitalized Patients.

INTRODUCTION -CONCEPTION OF THE IDEA OF THE STYDY The erythrocytic index RDW is a parameter of red blood cells, expresses anisocytosis in the red blood population (11.5-14.5%) and its values are determined in the routine blood count of 25 parameters. (1,2,3)The medical literature shows that a raised RDW is associated with an increased risk of death in a number of pathological conditions, heart disease, lung disease, stroke, sepsis, cancer.(4,5,6,7) With the burst of publications concerning Covid-19 disease, there is extensive reference to the relationship of RDW with the severity and mortality of the disease. (8,9,10,11,12,13) Similarly, lower platelet counts (PLTs) - thrombocytopenia are common in Covid-19 disease, through a variety of mechanisms and are related to its severity and outcome, as reported in a systematic review of 24 studies,(14) but also in a meta-analysis of 9 studies where, despite the great heterogeneity among them, the more sizeable drop of platelets was observed in non-survivors.(15,16,17) In addition, although covid-19 disease affects mainly the respiratory system and can lead to respiratory failure, it also comes with a high number of thromboses with raised D-dimers and findings of micro thrombosis in the lungs or other organs of the affected deceased. To the coagulopathy of covid-19 disease that resembles but is not identical to other coagulation disorders such as sepsis-DIC (SIC/DIC), hemophagocytic syndrome (HPS), antiphospholipid syndrome (APS) and thrombotic microangiopathy (TMA),(18) contributes, the overactivation of platelets and immunothrombosis that often occurs in severe covid-19 disease.(19) In the systematic review by Daniels and colleagues, 32 studies were found that examined markers related to platelet size (Platelet Volume Indexes, PVI) in relation to the severity or mortality of covid-19 disease.(20) The PVI parameters in these studies included, in addition to platelet count PLT and MPV, others, such as PDW, P-LCR, LMR, MPR, to a varying degree and combination. The results showed a general trend that high values of these markers are associated with disease severity and mortality.(20) The 14 studies of the review, reported significant differences in baseline PVI values between severe and mild covid-19 disease, although the longitudinal studies showed varying trends in these platelet markers.(20) In recent years, researchers have been interested in the platelet index MPV/PLT ratio (derived from the ratio of mean platelet volume to platelet count) as a specific marker of platelet-based systemic thrombogenicity.(21,22,23)

AIM OF THE STUDY Our study will examine the relationship of the red cell index RDW, platelet count PLTs and platelet index MPV/PLT ratio, with the risk of mortality in hospitalized patients with SARS-COV2, at entry, discharge, 1st week , 2nd week, as well as the total duration of hospitalization. There are no other reports on this issue in Greece.

If there is a connection and we determine the cut off values we could suggest that Hematology Laboratory may have the potential to assist in early screening and prognosis of COVID-19 disease.

Study Protocol and Patients Group The registered diagnosed with SARS-Cov-2 patients are either directly admitted to the General Hospital Sismanoglio - A.Fleming or coming for continuance of treatment from other hospitals of 1st Health Region of Attica mainly, such as: G.Gennimatas GH, Evangelismos GH, Konstantopoulio GH, Laiko GH, Erythros GH, Alexandra GH, Ippokrateio GH, Attikon GH, with information notes and laboratory data at their admission and hospitalization.

Hematological laboratory testing has been performed on Hematology Analyzers who are subject to Internal and External Quality Control. Regarding the General Hospital Sismanoglio - A. Fleming , the Hematology and Hemostasis Analyzers used, were ADVIA 2-120 , Sysmex Ca-1500, BCS XP by Siemens Healthineers and SYSMEX XE 2100 by Roche Diagnostics.

Patients will be enrolled according to age, gender, comorbidities, covid-19 disease severity, outcome (improvement or death), RDW, PLT, MPV/PLT ratio, parameters, at entry, discharge and mean values of hospitalization duration. To monitor the parameters' trend, the mean values of PLT, MPV/PLT ratio of the 1st and 2nd week of hospitalization will be determined and recorded, the nadir values of PLT, mean and nadir values of lymphocytes (absolute number, percentage% and when), mean and zenith values of CRP and D-dimers, as well as the score for DIC of the deceased, based on ISTH criteria.(24) (Table 1) MPV/PLT ratio is defined and calculated as : : MPV value (fl)x100/ PLT per 1000/μl

The 1st and 2nd week intervals were of interest because between the 7th and 14th day from the onset of the disease, there is a surge of clinical manifestations, with a pronounced increase in inflammatory mediators and cytokines. (25) The values of D-dimer (fibrin degradation products) will be determined and recorded as indicative of endovascular thrombosis and as an independent predictor of mortality risk in covid-19 disease. (26) Lymphocyte values (mean, absolute number, percentage % nadir and when) are also recorded, as lymphopenia is a predominant finding in most severe cases of covid-19 disease (15, 27, 28, 29) and the sequential assessment of lymphocyte dynamics can be predictive of the patient's outcome.(28) The CRP value (mean, zenith and when) is determined and recorded as an indicator of inflammation, especially high in the cytokine storm that can occur in covid-19 patients and is associated with disease mortality. (30) The classification of patients into mild/moderate and severe/critical covid-19 disease was based on the criteria of National Public Health Organization of Greece (EODY).(31) The statistical analysis will be performed by SAS Software for Windows version 9.4 (SAS Institute Inc, NC, USA). For the analysis of variables expressed as numeral values, i.e. quantitative data (e.g., age, RDW, PLTs etc.) and specifically to identify for differences between survivors and non survivors, the statistical analysis is expected to be performed via the Mann-Whitney U test method. However, in case that data do follow the normal distribution as evaluated by the Kolmogorov-Smirnov test then the t-test method will be applied. For the evaluation of differences in the expression of RDW and PLTs and MPV/PLT ratio or other numerical data in various groups (such as different age groups ) the Kruskal Wallis method will be applied and in case of normality will be applied the ANOVA test. Categorical data differences in the study groups (e.g. gender, age groups etc.) will be tested by the x2 test and if required via the Fisher exact test.

The level of statistical significance is set to <0.05 (P <0.05) and all tests will be two-sided.

Finally, the statistical analysis is composed of descriptive statistics, i.e. for numerical variables measures of central values and dispersion such as mean value, median, standard deviation and quartile 1 and 3 (Q1 and Q3) and for categorical variables includes percentages and 95% confidence intervals. For the inferential statistics it will be evaluated the hypothesis that RDW and PLTs, MPV/PLT ratio, values as prognostic markers for the final outcomes of COVID-19 hospitalized patients.

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31. : https://eody.gov.gr/wp-content/uploads/2022/04/covid_19_algorithmos-mi-nosileuomenon_20220404.pdf