Change of neutrophil-to-monocyte ratio to stratify the mortality risk of adult patients with trauma in the intensive care units

Background: The subtypes of circulating white blood cells undergo relative changes under systemic inflammation; thus, the derived ratio may reflect patients' immunoinflammatory status. Under the hypothesis that change in segmented neutrophil-to-monocyte (SeMo) ratio, delta-SeMo ratio, may reflect the host's immunoinflammatory response against illness, this study aims to investigate the effectiveness of using delta-SeMo ratio to assess the mortality risk of patients with trauma and critical illness. Materials and Methods: A total of 1476 adult patients with trauma admitted to the intensive care unit (ICU) between January 1, 2009, and December 31, 2020, were enrolled in this study. Delta-SeMo ratio was defined using the following formula: SeMo ratio at day 3 (72-96 h after admission into ICU)-SeMo ratio at admission (at admission into ICU). The primary outcome was inhospital mortality. Results: There was no significant difference in the SeMo ratio at admission between death and survival patients (18.7 ± 11.0 vs. 18.7 ± 18.4, P = 0.974); however, SeMo ratio at day 3 (20.3 ± 15.5 vs. 15.7 ± 16.0, P = 0.002) and delta-SeMo ratio (1.6 ± 19.5 vs.-3.0 ± 24.2, P = 0.034) of the patients who died were significantly higher than those of the patients who survived. The patients with delta-SeMo ratio ≥1.038, an estimated cutoff value for best predicting mortality by the plotted receiver operating characteristic curve, sustained an approximately 2-fold adjusted mortality (adjusted odds ratio [AOR]: 1.84, 95% confidence interval [CI]: 1.27-2.66, P = 0.001) than those with a delta-SeMo ratio <1.038. Furthermore, when the delta-SeMo ratio was set at 0, a threshold value indicating a condition with an increase or decrease in the SeMo ratio at day 3 than the SeMo ratio at admission, there was a 1.7-fold higher adjusted mortality (AOR: 1.70, 95% CI: 1.18-2.46, P = 0.004) of the patients with delta-SeMo ratio ≥0 than those with delta-SeMo ratio <0. Conclusion: Following trauma injury, critically ill patients with an increased SeMo ratio present with a higher rate of mortality and longer stay in the hospital and ICU than those with a decreased SeMo ratio. The use of the delta-SeMo ratio may help physicians quickly identify patients at higher risk of inhospital mortality.