Association between red blood cell distribution width and the prognosis of brain death in patients with a Glasgow Coma Scale < 6

Red blood cell distribution width (RDW) has been reported as a meaningful prognostic factor in various diseases. Our study compared patients’ RDW levels and prognosis at admission and discharge time. A total of 128 patients 77 patients who suffered brain death (subject group), and 51 patients who were discharged from the hospital (control group) with GCS ≤ 6 were recruited from 60 hospitals for this study. Demographical data and RDW measurements in these patients at admission time and brain death/discharge time were extracted into two groups. 46 (35.9%) patients were females and 82 patients (64.1%) were males with a median age of 36 years old. A significant difference in baseline characteristics of GCS (P < 0.001), RDW at admission time (P < 0.001), and RDW at discharge or brain death time (P < 0.001) were noted between the two groups. In the overall population, RDW at admission time had a median value of 13.75% and was positively correlated with gender (P < 0.04, rs = 0.582) and age (P < 0.023, rs = − 0.201). Initially, there were no significant differences in RDW upon admission. However, upon discharge, although the RDW in the control group was not significant (P < 0. 1), the RDW level at the time of brain death was notably 0.45 fold higher (P = 0.001) compared to the time of admission. The standardized residuals at the two-time points showed an approximately normal distribution. The most effective RDW cut-off in Brain death was determined as 14.55. Based on the findings, using RDW as a prognostic factor has a sensitivity of 0.468 and a specificity of 0.137 in diagnosing brain death. RDW biomarker is a simple and inexpensive laboratory test that may be seen as a valuable perspective for initial patient evaluation. RDW is a powerful marker for the prognosis of brain death in patients with a GCS ≤ 6 at admission time, in order to identify a subset of patients who may require more aggressive management in the trauma center.


Statistical analysis.
After evaluating the normality of the data using the Shapiro-Wilk test, descriptive statistics (frequency, mean and standard deviation) were studied.Changes in RDW at different time points were evaluated using a paired T-test.The strength of the association between RDW and clinical variables was assessed by univariate linear regression.An independent sample t-test was performed to compare the results between the study subjects and the controls.The mean changes of RDW level among the three groups were assessed with repeated measure analysis of variance.The receiver operating curve was used to determine the validity of different parameters in separating cases with RA from controls and the area under the curve (AUC).Meanwhile, the sensitivity, specificity, and cut-off values were calculated.In all analyses, a significance level of less than 0.05 was considered in SPSS16.

Ethical approval.
Ethical approval to report this case was obtained from * Tehran University of Medical Sciences (IR.TUMS.IKHC.REC.1400.020)*.

Participation informed consent.
Informed consent was obtained from all subjects' legal guardians to participate in this research.NO organs/tissues were procured from prisoners.
Statement of informed consent.Written informed consent was obtained from a legally authorized representative(s) for anonymized patient information to be published in this article.

Results
According to the obtained results, the mean age of the participants was 31.58 ± 15.54 (median age: 30 years).In addition, 82 (64.1%) of the participants were male, and 60 (46.68%) of the cause of brain death was head trauma.The mean and the median of the demographic data are shown in Table 1.
Additionally, 5.27 ± 4.07 days was the time interval between admission and brain death confirmation.The main characteristics of the study samples are reflected in Table 1.
A significant difference in baseline characteristics of GCS (P < 0.001), RDW at admission time (P < 0.001), and RDW at discharge or brain death time (P < 0.001) were noted between the two groups.(Tables 1, 2).
Furthermore, we also divided the cause of brain death into traumatic and non-traumatic groups in the subject group.An ANOVA test revealed that RDW levels at admission time and at the time of brain death were consistently higher in the traumatic patients' group compared to the non-traumatic ones (P = 0.008).www.nature.com/scientificreports/Based on Table 2, the RDW levels were constantly increasing throughout the study.There were no significant differences between RDW at admission time (13.38 ± 2.33) and RDW at discharge time (13.76 ± 2.12) in the control group (P = 0.1).
In contrast, RDW level at the time of brain death (16.36 ± 1.92) was higher compared to the time of admission (14.46 ± 1.89).The standardized residuals at the two-time points showed an approximately normal distribution (reflected in Fig. 1).
After relevant confounder adjustment using the univariate regression model, RDW value (OR 1.475, 95% confidence interval 1.16-1.86,P = 0.001) was an independent variable for brain death.Participants with RDW in the highest quartile had a fully adjusted hazard ratio for brain death compared with those with RDW in the www.nature.com/scientificreports/lowest quartile.Higher levels of RDW at admission time were also associated with an increased risk of brain death (P = 0.007).ROC curves of RDW levels were used to identify brain-dead group with a statistically significant level (area under the curve of 0.737; 95% confidence interval [CI], 0.645-0.829).As shown in Fig. 2, the best cut-off level for RDW in Brain death was 14.55.RDW in the diagnosis of brain death prognosis had a sensitivity of 0.468 and a specificity of 0.137.

Discussion
Previous studies explored the elevations in RDW levels associated with elevated inflammatory markers 16 , Previous studies explored the relationship between RDW and prognosis in patients with breast cancer 17 , Multiple Sclerosis (MS) 18 , and coronary artery disease 19 .
The role of RDW as a prognostic factor for brain death patients with GCS ≤ 6 is unclear.
Our study of the patients with GCS ≤ 6 showed a meaningful RDW increase in the brain death group compared to non-brain-dead patients.
The cut-off of 14.55% in the ROC curve demonstrated that RDW is a specific and sensitive biomarker for diagnosing brain death.According to our results, RDW may be a prognostic factor for brain death in patients with GCS < 6.
New markers with prognostic features can help to identify vulnerable patients and optimize patient care and management in high-risk groups 20 .Based on our results more attention should be paid to patients with a higher RDW at admission time.
To the best of our knowledge, there have been few studies investigating RDW as a prognostic factor of brain death.We were able to locate only one study by Nevzat Mehmet that identified RDW as a predictor of brain death.The study documented that RDW levels on the days of brain death and cardiac arrest were significantly higher than on the day of admission 21 .
Consist of our results, Lippi et al. showed significant RDW increase levels in traumatic patients upon admission compared to others.According to their findings, patients who had experienced trauma were three times more likely to have higher RDW values than those who had not experienced trauma 22 .
Zhang et al. 23 , showed that RDW might be a reliable prognostic biomarker for Traumatic brain injury mortality.
Similar to our results, Lee et al. 24 revealed that RDW can independently predict mortality in trauma patients.On the contrary, Sadaka et al. demonstrated that RDW was a poor prognostic factor of mortality with an AUC value of 0.66 in traumatic brain injury patients 16 .
Results have shown a correlation between RDW, gender, and age.Like our finding, Hoffmann et al. 25 found a strong association between RDW and age; however, they didn't find any association between RDW and gender.

Conclusion
In a retrospective study of 162 patients, we found that RDW is a powerful marker for the prognosis of brain death, in order to identify a subset of patients who may require more aggressive management in the trauma center 22 .In cases with loss of consciousness due to head injury, a high level of RDW could be associated with a higher risk of brain death.Therefore, RDW is a simple and inexpensive biomarker that could be seen as a valuable perspective for initial patient evaluation 22 .Utilizing these findings could aid in identifying the patients who would benefit from more aggressive management.
Considering the study's novelty, there was no similar research data to reference, resulting in some limitations in the study.It was a retrospective study with a small number of patients in both groups.Some patients were excluded from the study, given the abovementioned inclusion criteria.To improve future studies, we recommend increasing the number of patients and expanding the inclusion criteria, such as GCS to > 6. www.nature.com/scientificreports/ The strength of this research was the distribution of all hospitals in Iran.Therefore, our results may be applicable to other organizations with different patient populations and larger sample sizes with a wider variety of socio-demographic characteristics.Clearly, more studies are needed to confirm the validity of the present results in a larger population. https://doi.org/10.1038/s41598-023-39836-6

Figure 2 .
Figure 2. The relative operating characteristic (ROC) curve of RDW values for predicting brain death.

Table 1 .
Baseline characteristics of study population.

Table 2 .
The level of RDW in interval study period.
Figure 1.RDW values at admission time and time of brain death in the subject group compared to RDW values at admission time and time of discharge in the control group.Vol:.(1234567890)Scientific Reports | (2023) 13:14027 | https://doi.org/10.1038/s41598-023-39836-6