The effect of body mass index extremes on immune-inflammatory markers and outcomes in trauma patients

Background: Body mass index (BMI) extremes, including underweight and extreme obesity, are associated with unique health challenges and increased risk of complications in trauma patients. Immune-inflammatory markers, such as neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), and systemic immune-inflammation index (SII) are widely used prognostic indicators. However, their role in trauma patients with extreme BMI remains unclear. Methods: This retrospective cohort study analyzed trauma registry data from a single institution between 2009 and 2023. Adult trauma patients aged ≥20 years were categorized into underweight, normal weight, and extreme obesity groups (BMI, <18.5, 18.5–24.9, and ≥40 kg/m2, respectively). NLR, MLR, PLR, and SII were calculated to evaluate the immune-inflammatory responses. Propensity score matching was performed to control for confounders such as age, sex, comorbidities, and injury severity. Results: Of 54,313 initially screened trauma patients, 19,967 were included. The underweight group exhibited higher MLR (0.45 vs. 0.39 vs. 0.41, p = 0.001), NLR (7.80 vs. 6.56 vs. 7.24, p = 0.003), and PLR (180.69 vs. 166.66 vs. 169.99, p = 0.004) than extreme obesity and normal weight groups. The underweight group also had the highest mortality rate (3.4% vs. 2.0% vs. 0.6%, p < 0.001), whereas the extreme obesity group had the longest hospital stay (10.7 vs. 8.7 days, p = 0.029). After propensity score matching, most immune markers showed no significant differences between the groups, except for monocyte counts, which remained significantly higher in the extreme obesity group (569.8 vs. 502.8/µL, p = 0.032). Conclusions: BMI extremes affect inflammatory profiles and trauma outcomes before matching, with patients having underweight demonstrating increased inflammatory ratios and mortality, and those with extreme obesity exhibiting prolonged hospital stay and elevated monocyte counts. Despite no significant differences in most immune markers after matching, these findings highlight the need for further studies on the interplay between BMI, immune response, and trauma recovery.

BMI extremes; Trauma outcomes; Immune-inflammatory markers; Neutrophil-to-lymphocyte ratio; Propensity score matching

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