Emerging Alzheimer disease blood biomarkers show significantly reduced accuracy in individuals with a history of traumatic brain injury (TBI), according to a new study of older veterans.
Researchers analyzed banked plasma from 272 Vietnam War veterans, all without dementia but some with mild cognitive impairment. The study evaluated the plasma p-tau217/Aβ42 ratio, a leading test for detecting amyloid brain plaques.
The findings reveal a sharp decline in diagnostic performance tied to TBI severity. For veterans without a TBI, the blood test was 90% accurate. Accuracy fell to 78% for those with a TBI involving loss of consciousness for up to 5 minutes, and plummeted to 63% for those unconscious for more than 5 minutes.
The declining accuracy was primarily driven by low sensitivity, meaning the test frequently missed amyloid pathology in patients with a TBI history. This raises a serious clinical concern, as the blood test might miss more than half of amyloid-positive cases in this group.
The study authors advise caution when interpreting these results, emphasizing that TBI history and severity can substantially modify biomarker performance as blood-based diagnostics become more common.