Effect of prior traumatic brain injury on Alzheimer’s disease blood biomarkers in Vietnam Veterans

Importance: Traumatic brain injury (TBI) is a risk factor for dementia and is known to impact levels of several Alzheimer's disease (AD) blood biomarkers. Plasma pTau217/ Aβ42 ratio has been reported to be 90% accurate for detection of brain amyloid in civilian cohorts. Objective: To evaluate the accuracy of emerging AD blood biomarkers in Veterans with and without TBI history. Design: We assessed the performance of the FDA-approved plasma pTau217/Aβ42 ratio and plasma levels of pTau217 and Aβ42/40 ratio for detecting brain amyloid-β positivity (e.g., amyloid-PET consensus visual read). We compared biomarkers' accuracy in Veterans with no TBI (N=93), TBI with loss of consciousness (LOC) 0-5 minutes (N=89), and TBI with LOC >5 minutes (N=90). Setting: Cross-sectional cohort study using existing data and banked plasma from the Alzheimer's Disease Neuroimaging Initiative Department of Defense (ADNI-DOD) study. Participants: 272 older Vietnam Veterans without dementia (83% cognitively unimpaired, 17% mild cognitive impairment), median (IQR) age 69 (67,72) years, 270/272 male, who had amyloid-PET and concurrently collected banked plasma available for analysis. Results: