In‐hospital mortality in SARS‐CoV‐2 stratified by hemoglobin levels: A retrospective study

Abstract This study is to estimate in‐hospital mortality in severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) patients stratified by hemoglobin (Hb) level. Patients were stratified according to hemoglobin level into two groups, that is, Hb <100 g/L and Hb >100 g/L. A total of 6931 patients were included. Of these, 6377 (92%) patients had hemoglobin levels >100 g/L. The mean age was 44 ± 17 years, and 66% of the patients were males. The median length of overall hospital stay was 13 days [2; 31]. The remaining 554 (8%) patients had a hemoglobin level <100 g/L. Overall mortality was 176 patients (2.54%) but was significantly higher in the group with hemoglobin levels <100 g/L (124, 22.4%) than in the group with hemoglobin levels >100 g/L (52, 0.82%). Risk factors associated with increased mortality were determined by multivariate analysis. The Kaplan‐Meier survival analysis showed hemoglobin as a predictor of mortality. Cox proportional hazards regression coefficients for hemoglobin for the HB ≤ 100 category of hemoglobin were significant, B = 2.79, SE = 0.17, and HR = 16.34, p < 0.001. Multivariate logistic regression showed Hb < 100 g/L had a higher cumulative all‐cause in‐hospital mortality (22.4% vs. 0.8%; adjusted odds ratio [aOR], 0.33; 95% [CI]: [0.20–0.55]; p < 0.001). In this study, hemoglobin levels <100 g/L were found to be an independent predictor of in‐hospital mortality.

of mortality. Cox proportional hazards regression coefficients for hemoglobin for the HB ≤ 100 category of hemoglobin were significant, B = 2.79, SE = 0.17, and HR = 16.34, p < 0.001. Multivariate logistic regression showed Hb < 100 g/L had a higher cumulative all-cause in-hospital mortality (  .55]; p < 0.001). In this study, hemoglobin levels <100 g/L were found to be an independent predictor of in-hospital mortality. infection, the level of serum hemoglobin remains a predictor of adverse events. Low hemoglobin (Hb) levels in SARS-CoV-2 are associated with the development of respiratory failure. The requirement for mechanical ventilation was observed to be higher with low Hb levels [1]. Low hemoglobin levels in the setting of SARS-CoV-2 pneumonia may exacerbate O2 desaturation and are a predictor of poor prognosis [2]. Disseminated intravascular coagulation-related low Hb levels are seen in SARS-CoV-2 [3]. Many studies have shown that ventilator-dependent critically ill SARS-CoV-2 patients have low Hb levels [4]. Anemia is an independent predictor of severe SARS-CoV-2 infection as well as overall mortality [5].

METHODS
Participants and the study design comprised a total of 6931 confirmed

STATISTICAL ANALYSIS
Descriptive statistics are used to present the data. Categorical variables are summarized as frequencies and percentages and were analyzed using Pearson's χ 2 test. Continuous variables are summarized using the mean and standard deviation. To evaluate the impact of Hb level (Hb <100 g/L and Hb >100 g/L) on all-cause mortality, we used multivariable logistic regression. The odds ratios (ORs) for in-hospital all-cause mortality status were adjusted for sex, age, white blood cells, platelet counts, neutrophils, and hemoglobin levels.
A Cox proportional hazards model was performed to determine whether hemoglobin had a significant effect on the hazard of mortality.
The live category of mortality was used to indicate survival while the dead category was used to represent a hazard event. The level of significance was set at p < 0.05 a priori. Statistical analyses were conducted using R statistical packages [6] and SPSS version 27 (SPSS, Chicago, IL, USA).

RESULTS
A total of 6931 SARS-CoV-2-positive patients were included in the study; the mean patient age was 44 ± 17 years, and 66% of the patients were male. We observed that 6377 (92%) of the patients had hemoglobin levels >100 g/L. The median length of overall hospital stay was 13 days [2; 31]. In this study, 554 (8%) patients had a hemoglobin level <100 g/L. The overall mortality was 176 patients (2.54%), and the mortality rate was higher in the group with hemoglobin levels   Figure 1).

DISCUSSION
The observations from this multicenter observational study showed that SARS-CoV-2 patients with lower hemoglobin levels are at higher risk of in-hospital mortality than those with higher levels of >100 g/L.
In this study, lower hemoglobin levels were found to be an independent predictor of in-hospital mortality. Male sex had a significant impact on cumulative all-cause in-hospital mortality among the group with low hemoglobin levels. Among the two groups, age showed no significant impact on all-cause cumulative in-hospital mortality.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

ETHICS APPROVAL STATEMENT
This study was approved by the ethics committee and Ministry of Health Kuwait.

PATIENT CONSENT STATEMENT
Patient consented was not mandated for this retrospective observational study. Permission to reproduce material from other sources: No material from other sources is included in this study.

CLINICAL TRIAL REGISTRATION
This study was not a clinical trial.

NOVELTY STATEMENT
This study mainly focused on the clinical significance of hemoglobin levels while treating SAR-CoV-2 infection. These results will help the clinicians to categorize the patients as the low hemoglobin levels were proven to be an independent predictor in-hospital mortality. This will help the clinicians for early initiation of critical care strategies for such patients and thereby may reduce mortality and related complications to an extent.