Prognostic Evaluation of Red Blood Cell Distribution Width (RDW) in Severe and Critical COVID-19 Patients Monitored in the Intensive Care Unit
Conditions: COVID - 19, Prognosis, ICU
Sponsor: Ankara University

Date of Issue: June-1-2024 
Prognostic evaluation of red blood cell distribution width (RDW) in severe and critical 
COVID-19 patients monitored in the intensive care unit 
 
1. Methodology: 
Retrospective, single-center, observational study. 
This retrospective study included data from severe and critical COVID-19 patients admitted 
to the COVID-19 Intensive Care Unit of Ankara University Ibn-i Sina Research and Practice 
Hospital, Department of Anesthesiology and Reanimation, between June 2020 and May 2024. 
 
2. Objective of the Study: 
COVID-19 has caused significant morbidity and mortality worldwide, particularly among 
critically ill patients. Early identification of patients at high risk for poor outcomes is crucial. 
Red cell distribution width (RDW), a measure of the variation in red blood cell size, has 
emerged as a potential marker of inflammation and has been associated with adverse 
outcomes in various medical conditions, including COVID-19. 
This study aims to investigate the relationship between RDW and mortality in severe and 
critical patients admitted to our COVID-19 intensive care unit. 
• 
Primary Objective: To determine whether RDW can serve as a prognostic marker for 
mortality in severe and critical COVID-19 patients admitted to the ICU. 
• 
Secondary Objective: To evaluate the association of RDW with adverse outcomes 
such as invasive mechanical ventilation, duration of intubation, and secondary organ 
damage in severe and critical COVID-19 patients admitted to the ICU. 
 
3. Inclusion Criteria: 
• 
Patients over 18 years of age 
• 
Severe and critical COVID-19 patients (with positive PCR test or diagnosed clinically 
and radiologically) 
• 
Patients followed in the ICU for at least three days 
• 
Patients without hematological malignancy 
COVID-19 severity was classified according to the Diagnosis and Treatment Protocol for 
Novel Coronavirus Pneumonia (Trial Version 7) published by the National Health 
Commission of the People’s Republic of China: 
• 
Severe cases: Meeting any of the following criteria: 
o Respiratory rate (RR) ≥ 30 breaths/min 
o Resting oxygen saturation (finger) ≤ 93% 
o Arterial partial pressure of oxygen (PaO₂)/fraction of inspired oxygen (FiO₂) ≤ 
300 mmHg 

o 50% progression of lung lesions within 24–48 hours on imaging 
• 
Critical cases: Meeting any of the following criteria: 
o Respiratory failure requiring mechanical ventilation 
o Shock 
o ICU admission required due to organ failure other than respiratory failure 
Reference: National Health Commission & National Administration of Traditional Chinese 
Medicine. (2020). Diagnosis and treatment protocol for novel coronavirus pneumonia (Trial 
Version 7). Chinese Medical Journal, 133(09), 1087-1095. 
 
4. Exclusion Criteria: 
• 
Patients under 18 years of age 
• 
Patients with hematological malignancies (since RDW levels may be affected) 
• 
Patients who died within three days of ICU admission 
 
5. Data Collection: 
Patient demographics, clinical features, laboratory results (including RDW), and outcomes 
will be collected from electronic medical records and patient files. 
To ensure patient confidentiality, data will be anonymized. Since all data will be de-identified 
and analyzed retrospectively, no direct patient contact will be required. 
Data to be recorded: 
• 
Demographics: Sex, age, body mass index (BMI), number and type of COVID-19 
vaccines 
• 
Comorbidities 
• 
Hospitalization data: Referring department, length of stay, outcome 
(mortality/discharge), discharge destination 
• 
At ICU admission: APACHE II and SOFA scores, days from symptom onset to 
hospital admission, type of respiratory support, hematological and biochemical 
laboratory results 
• 
During follow-up: Trends in hematological and biochemical laboratory parameters 
(increase/decrease/normalization), need for invasive/non-invasive mechanical 
ventilation, duration of intubation, antiviral therapy, development of secondary 
infections, development of secondary organ failure, mortality/discharge 
6. Statistical Analysis 
• 
Sample Size Calculation 
The main hypothesis of the study was to investigate whether there is a difference in 
RDW levels between patients who survived and those who did not. Based on the study 
by Lorente et al. (2021), which reported RDW values of 13.4 ± 1.5 and 14.5 ± 2.2, an 
effect size of 0.58 was calculated. At a significance level of 0.05 and a statistical 
power of 0.80, the required sample size was determined to be 110 patients in total. The 
sample size calculation was performed using the G*Power software (version 3.1.9.2). 

• 
Statistical Methods 
Descriptive statistics will be presented as mean ± standard deviation (min–max) for 
normally distributed quantitative variables, as median (min–max) for non-normally 
distributed variables, and as percentages for categorical variables. To compare two 
independent groups, the Independent Samples t-test will be used when assumptions are 
met, while the Mann-Whitney U test will be applied otherwise. Relationships between 
categorical variables will be evaluated using the Chi-Square test, Fisher’s exact test, 
or multi-way Chi-Square test, as appropriate. For comparisons involving more than 
two groups, One-Way ANOVA or the Kruskal-Wallis test will be applied depending on 
the distribution of data. All statistical analyses will be performed using SPSS software 
(version 11.5). 
 
7. Ethical Considerations 
• 
Confidentiality: All patient data will be de-identified and securely stored. Access to 
the data will be restricted to authorized research personnel only. The data will be kept 
in a secure database with access limited to the research team. 
• 
Risk to Participants: Since this is a retrospective study utilizing existing medical 
records, there is no direct risk to participants. The study does not involve any 
intervention and does not cause any harm to patients whose records are analyzed. 
• 
Benefits: The potential benefits of this study include a better understanding of 
prognostic markers in COVID-19, which may improve patient care and resource 
allocation in intensive care units. This could contribute to better patient outcomes and 
more efficient use of healthcare resources. 
• 
Informed Consent: Given the retrospective design of the study and the use of de-
identified data, obtaining informed consent from patients was not feasible. Since the 
study poses no more than minimal risk to participants and does not involve procedures 
for which written consent is normally required outside the research context, a waiver 
of informed consent was requested and approved by the ethics committee.