Association of admission aggregate index of systemic inflammation with lower-extremity deep vein thrombosis after severe trauma.

Early identification of patients at risk for lower-extremity deep vein thrombosis (LEDVT) after severe trauma remains difficult. This retrospective cohort study evaluated whether admission aggregate index of systemic inflammation (AISI), derived from platelet, neutrophil, monocyte, and lymphocyte counts, was associated with ultrasound-confirmed in-hospital LEDVT detected before the earlier of discharge or post-injury day 30 and whether it improved risk stratification. Among 223 adults with an Injury Severity Score of 16 or higher and evaluable bilateral lower-extremity ultrasonography, 93 (41.7%) had LEDVT. Each 1-SD increase in log-transformed AISI was associated with LEDVT after adjustment for age, sex, Injury Severity Score, Glasgow Coma Scale score, and shock index (odds ratio [OR], 2.07; 95% CI, 1.47-2.91; P < 0.001) and after additional adjustment for D-dimer, fibrin/fibrinogen degradation products, prothrombin time, activated partial thromboplastin time, and fibrinogen (OR, 1.86; 95% CI, 1.26-2.73; P = 0.002). Adding AISI to clinical variables increased the area under the receiver operating characteristic curve (AUC) from 0.619 to 0.714 (AUC difference, 0.095; bootstrap 95% CI, 0.023 to 0.168; P = 0.009). After coagulation markers were included, the AUC difference was smaller and uncertain (0.018; 95% CI, -0.010 to 0.046; P = 0.166), although the Brier score improved by 0.014 (P = 0.020). For Model 4, bootstrap-corrected and repeated-cross-validation AUCs were 0.797 and 0.790, and calibration slopes were 0.831 and 0.773, respectively. With 93 events and 11 candidate parameters, these internally validated results indicate shrinkage and require prospective external validation; AISI should be interpreted as a complementary admission marker.