Age, admission platelet count, and mortality in severe isolated traumatic brain injury: A retrospective cohort study

Background: We asked whether patients >50 years of age with acute traumatic brain injury (TBI) present with lower platelet counts and whether lower platelet counts are independently associated with mortality. Methods: We combined trauma registry and laboratory data on a retrospective cohort of all patients >= 18 years of age admitted to our Level 1 US regional trauma center 2015-2021 with severe (Head Abbreviated Injury Score [AIS] >= 3), isolated (all other AIS <3) TBI who had a first platelet count within 1 h of arrival. Age and platelet count were assessed continuously and as groups (age 18-50 vs. >50, platelet normals, and at conventional transfusion thresholds). Outcomes such as mean admission platelet counts and in-hospital mortality were assessed categorically and with logistic regression. Results: Of 44,056 patients, 1298 (3%, median age: 52 [IQR 33,68], 76.1% male) met all inclusion criteria with no differences between younger and older age groups for (ISS; 18 [14,26] vs. 17 [14,26], p =.22), New ISS (NISS; 29 [19,50] vs. 28 [17,50], p =.36), or AIS-Head (4 [3,5] vs. 4 [3,5]; p =.87). Patients aged >50 had lower admission platelet counts (219,000 +/- 93,000 vs. 242,000 +/- 76,000/mu L; p <.001) and greater in-hospital mortality (24.5% vs. 15.6%, p <.001) than those 18-50. In multivariable regression, firearms injuries (OR9.08), increasing age (OR1.004), NISS (OR1.007), and AIS-Head (OR1.05), and decreasing admission platelet counts (OR0.998) were independently associated with mortality (p <.001-.041). Platelet transfusion in the first 4 h of care was more frequent among older patients (p <.001). Conclusions: Older patients with TBI had lower admission platelet counts, which were independently associated with greater mortality.