The revised trauma score combined with the Injury Severity Score (ISS) remains the mostly commonly used system for predicting trauma mortality, but these scoring systems do not account for the patient's comorbidities. This study aims to evaluate the effect of comorbidities on ISS-related mortality and length of stay. A review of our trauma center's data registry from 2014 to 2016 was carried out. Patients were divided according to ISS into two groups: ISS ≤ 15 and ISS > 15. Each ISS group was then subdivided by number of comorbidities into two groups: 1 to 2 or ≥3 comorbidities. Demographic characteristics and outcome measures were compared. ANOVA, chi-squared, and t tests were used with significance defined as P < 0.05. A total 9845 adult trauma patients were admitted to our trauma center during the three-year study period. In the ISS ≤ 15 group, patients with <3 comorbidities had significantly higher mortality rate compared with patients with 1 to 2 comorbidities (1.50% vs 0.12%, P ≪ 0.000007). Comparing the ISS ≤ 15 group with ≥3 comorbidities with the ISS > 15 group with 1 to 2 comorbidities, the mortality rate was significantly higher (23.40% vs 4.50%, P ≪ 0.000002). The ICU length of stay was significantly higher in the ISS ≤ 15 groups (17 vs 10 days, P < 0.05) but similar in the ISS > 15 groups (31 vs 29 days) (P > 0.05). It was concluded that when controlling for injury severity, increased comorbidities are associated with a significantly higher mortality, indicating that they may serve as a marker of lower physiologic reserve and be an independent variable. Adding comorbidity parameters to the current trauma scoring systems can assist in predicting more accurate/reliable outcomes.

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