The findings of the current study showed a strong relationship between RDW upon ICU admission and short-term mortality in critically ill patients with T2DM, with a greater RDW being linked to a higher death rate. The same relationship was observed in all subgroups. Moreover, the RDW increased more rapidly in the non-survivor group within 48 h after ICU admission, and the difference continued to increase, suggesting that patient prognosis may be better judged by combining the dynamic changes based on the RDW from baseline upon admission to the ICU.
RDW, a common clinical indicator, is a quantitative indicator of the heterogeneity of erythrocyte volume; its reduction has limited clinical significance, while its elevation reflects the aggravation of erythrocyte volume inequality. It was first used for the morphological classification of anemia [16]. In recent years, related studies have demonstrated the broader clinical of RDW and its close association with various organ dysfunctions and inflammatory reflections, with mechanisms that may involve oxidative stress, poor nutritional status, and abnormal lipid metabolism. Hence, RDW has demonstrated promising applications in intensive care and has been used to assess the prognosis of patients with sepsis, heart failure, and acute respiratory distress syndrome (ARDS) [17–19]. When combined with other standard ICU scores, including SOFA, logistic organ dysfunction system, Acute Physiology and Chronic Health Evaluation II, and SAPS II, Moreno-Torres et al. discovered that RDW was an independent predictive marker of mortality and enhanced the prediction of death [20]. According to Xiao et al., increased RDW is a significant risk factor for developing ARDS after severe burns and plays a significant role in predicting its development [21]. The findings of these studies imply that RDW could be useful in determining a patient’s prognosis when they are severely sick. Similar to those in previous research, the results of this study demonstrated that elevated baseline levels and sustained elevation within 48 h of RDW were independently associated with all-cause 28-day/60-day mortality in critically ill patients with T2DM. This association persisted after accounting for several confounding variables, indicating the importance of paying close attention to the elevated RDW in critically ill patients with T2DM.
The underlying mechanisms by which elevated RDW leads to increased mortality in patients with T2DM are not fully elucidated. However, they may be related to glycemic variability and diabetes-related complications. Several studies have reported an association between increased RDW and increased glycosylated hemoglobin (HbA1c) levels, which reflects the magnitude of glycemic variability in patients with diabetes. Furthermore, these studies reported that hyperglycemia shortens the lifespan of red blood cells, leading to a highly variable red blood cell volume or RDW, which is associated with increased mortality [22–25]. In addition, RDW is associated with the development of diabetes-related complications. Such complications, particularly cardiovascular complications, are the leading cause of death in patients with diabetes [1]. Nam et al. observed a higher incidence of carotid atherosclerosis among patients with high RDW after adjusting for various covariates in patients with T2DM without cardiovascular diseases [10]; RDW may be a crucial clinical predictor for the development of diabetic complications such as cardiovascular and urinary system disorders, according to Malandrino et al., who examined regular blood test results in a representative sample of US adult patients with diabetes [26]. Overall, these findings suggest a strong and complex association between RDW and diabetes.
All of the subgroup analyses in the current investigation showed associations between RDW and mortality in critically ill patients with T2DM, demonstrating the consistency of the findings. In addition, better RDW predictive power of mortality was observed in the non-older adult, no acute kidney injury, and no renal replacement therapy subgroups, suggesting a potential interaction between these variables and RDW, and that these patients could benefit more from RDW detection. However, the underlying mechanisms require further study. Subsequently, GAMM analysis revealed elevated RDW in the first 48 h of ICU admission in both the non-survivor and survivor groups, with a more rapid increase in the non-survivor group. The difference in RDW between the two groups remained significant and increased over time, suggesting that patients with persistently elevated and high RDW were at a higher risk of death.
There are a few restrictions on this research. Firstly, since this was a single-center retrospective study, selection bias was inevitable, and multicenter prospective investigations are needed to corroborate the findings. Secondly, the data in this study were obtained from an open clinical database, and information regarding past medical history related to diabetes, which may be associated with patient mortality, was lacking [27]. Information was also lacking regarding whether patients had received medications that could affect RDW during ICU treatment, which may have also affected the results.