Coronavirus disease (COVID-19) is an infectious disease caused by the SARS-CoV-2 virus.
According to official figures from the World Health Organization, the COVID-19 pandemic
has sickened 780 million people worldwide and caused more than 7 million deaths.

Common symptoms of COVID-19 include fever, cough, and shortness of breath. Symptoms such
as headache, sore throat, runny nose, muscle and joint pain, extreme fatigue, new-onset
loss of smell and taste, and diarrhea may also occur. While the disease can be
asymptomatic, severe cases can develop pneumonia, severe acute respiratory infection,
multiple organ failure, and death. Predicting high risk in patients with COVID-19 has the
potential to reduce mortality and morbidity by enabling early transfer of patients to
intensive care units and planning appropriate treatment. For this purpose, numerous
studies have been conducted to determine whether different markers can be used in
addition to risk scores such as APACHE and SOFA, which are currently used in intensive
care units. These markers include increased neutrophil and platelet counts, decreased
lymphocyte counts, and elevated levels of B-type natriuretic peptide (BNP), blood urea
nitrogen (BUN), creatine kinase (CK), bilirubin, interleukin-6 (IL-6), c-reactive protein
(CRP), procalcitonin, ferritin, alanine aminotransferase (ALT), albumin, and lactate
dehydrogenase (LDH). RDW (red blood cell distribution width), a measure of variation in
red blood cell size, has traditionally been used in the diagnosis of various
hematological conditions. In recent years, it has also been shown to be a potential
marker of inflammation.

Increased proinflammatory activity and hypoxia impair erythropoiesis, leading to an
increase in red cell distribution width (RDW) and changes in hematocrit. Increased RDW
has been associated with poor prognosis in other critical illnesses, such as sepsis and
cardiovascular disease. In COVID-19, viral inflammation can affect erythrocyte production
and turnover, leading to an increase in RDW. Increased RDW increases proportionally with
the degree of systemic inflammation and can therefore be a marker of disease severity.
Higher RDW values at hospitalization have been associated with increased mortality and
the need for intensive care. A meta-analysis of multiple studies has shown that high RDW
is a strong predictor of mortality in COVID-19 patients. This meta-analysis suggests that
RDW can be used as an early warning indicator to identify patients at high risk for
severe disease and adverse clinical outcomes. Other research supports the use of RDW as a
biomarker in COVID-19 and reinforces the role of RDW as a general marker of physiological
stress/disease severity. RDW, a low-cost parameter included in the standard complete
blood count, can be easily integrated into clinical practice, contributing to the early
identification of high-risk COVID-19 patients and facilitating the planning of timely and
appropriate medical interventions.

The aim of this study is to investigate the relationship between RDW values at admission
and the need for intubation in severely ill and critically ill patients admitted to
COVID-19 intensive care unit by analyzing the time course of RDW. Furthermore, the
relationship between RDW and other laboratory and clinical parameters will also be
investigated.

Materials and Methods: This retrospective study was conducted using data from patients
admitted to the COVID-19 intensive care unit at Ankara University Ibn-i Sina Research and
Application Hospital between April 2021 and August 2024. Among 758 patients admitted to
the intensive care unit (ICU) due to COVID-19 between the specified dates and who met the
World Health Organization's severe and critically ill COVID-19 criteria, 360 patients
were randomly selected.

Patients' demographic characteristics (age, gender, vaccination status), comorbidities,
length of stay in the ICU, need for intubation, laboratory parameters (RDW, hemoglobin,
platelet count, leukocyte count, neutrophil/lymphocyte (N/L) ratio, CRP, procalcitonin,
interleukin-6, etc.), and ICU severity scores (APACHE II and SOFA) were recorded. RDW
values were recorded for five consecutive days, starting from the first day of ICU
admission.

For statistical analyses, the Mann-Whitney U test was used to compare two independent
groups, the Chi-square test for categorical variables, and the Two-Way Repeated
Measurement ANOVA for repeated measurements. A P value of <0.05 was considered
statistically significant. The prognostic value of RDW and the optimal cut-off value were
determined using ROC analysis.