Predictive value of platelet function assays in traumatic brain injury patients on antiplatelet therapy

INTRODUCTION Traumatic brain injury (TBI) patients on antiplatelet therapy face higher mortality because of impaired platelet function, which may be treated by platelet transfusion. The value of testing platelet function in this cohort remains controversial. We aimed to evaluate the relationship between platelet function assays and outcomes in TBI patients on antiplatelet therapy receiving platelet transfusions. We hypothesized that the magnitude of change in platelet assay performance following a transfusion would predict meaningful clinical outcomes. METHODS A cohort of patients, aged 18 to 89 years, with a history of preinjury antiplatelet therapy or who required platelet transfusion, and who were deemed at risk for neurosurgical intervention, was selected from a prospective randomized controlled trial of platelet transfusion for TBI. Pre- and posttransfusion blood samples were drawn. Platelet hemostatic function assays (PHFAs) included thromboelastography with platelet mapping (TEG-PM) and VerifyNow. Logistic regression models assessed the association of temporal assay results with 30-day all-cause mortality, need for craniotomy, and initial and follow-up Rotterdam scores. RESULTS Data from 94 TBI patients (43% female) with a median age of 76 years were analyzed. The 30-day mortality rate was 14%. VerifyNow aspirin assay was able to capture increases in platelet function following a platelet transfusion in patients on aspirin (significant positive Δ = 65 aspirin response units, p < 0.001). Thromboelastography with platelet mapping parameters detected improved platelet function following transfusion, although the absolute value of changes was minimal. Thromboelastography with platelet mapping parameters predicted important clinical outcomes on logistic regression, although no significant associations with clinical outcomes were identified by the change in PHFA after transfusion or after adjusting for multiple comparisons. CONCLUSION Higher absolute pre- and posttransfusion values of TEG-PM were associated with decreased mortality, decreased need for neurosurgical intervention, and decreased risk of progression of hemorrhage in TBI patients taking antiplatelet agents, although neither the change in TEG-PM after transfusion nor any other PHFA value predicted outcomes. LEVEL OF EVIDENCE Prognostic and Epidemiological; Level III.