Blood Test for p-tau217 Shows Promise in Early Dementia Detection and Clinical Diagnosis
New research demonstrates that blood tests measuring p-tau217 protein can identify dementia risk up to 25 years before symptoms and significantly improve diagnostic accuracy in clinical practice.
A routine blood test measuring plasma phosphorylated tau 217 (p-tau217) may help identify women at higher risk of dementia up to 25 years before symptoms appear, according to a new study published in JAMA Network Open. Researchers in the US analysed blood samples from 2,766 cognitively healthy women aged 65–79 in the 1990s, tracking their cognitive health over the following 25 years to see who developed mild cognitive impairment (MCI) or dementia.
The team measured levels of p-tau217, a protein linked to tau tangles in the brain—a hallmark of Alzheimer's and other dementias. Higher p-tau217 levels strongly correlated with an increased risk of MCI and dementia, though not all women with high levels developed the disease. The link between higher p-tau217 and dementia was stronger in women over 70 and those carrying the APOE ε4 gene, known for its connection to Alzheimer's.
Blood-based biomarkers like p-tau217 are promising because they are far less invasive and more accessible than brain scans or spinal fluid tests. These tests could accelerate research and evaluate dementia risk-reduction strategies.
In a separate prospective observational study published in the Journal of Neurology, researchers evaluated whether implementing serum p-tau217 testing improves diagnostic accuracy in real-world clinical practice. The study included 200 consecutive participants (mean age, 72.15 years; 67.0% women) from a tertiary hospital in Spain between 2024 and 2025. Overall, 38.5% of participants had subjective cognitive decline, 47.5% had mild cognitive impairment, and 14.0% had dementia.
After receiving p-tau217 test results, the clinical diagnosis was changed in approximately 25% of participants, and the diagnostic confidence improved significantly from 6.90 ± 1.74 to 8.49 ± 1.68 (t test, -10.46; P < .001). Diagnosis was reclassified in mild cognitive impairment (chi square, 47.21) and dementia (chi square, 17.15) groups, and the diagnostic confidence significantly improved across all cognitive stages and in both clinical settings (P < .001 for all). Diagnostic agreement with the final diagnosis improved markedly, rising from 75.5% before testing to 94.5% after testing (kappa index, 0.576 vs 0.906).
Digital cognitive assessment tools are also being developed to work alongside p-tau217 testing. New data presented at a global Alzheimer's conference examined prediction of plasma p-tau217 status and Alzheimer disease risk using the remote-ready Digital Assessment of Cognition (DAC). The approach showed high classification accuracy and negative predictive value as a front-end screener, potentially helping to prioritize confirmatory testing and reduce unnecessary biomarker testing for low-likelihood candidates.
In the long-term women's study, elevated p-tau217 predicted dementia in both White and Black women, though no association was seen with MCI in Black women. Researchers suggest this could be due to misdiagnosis, differing disease mechanisms, or demographic and health differences that were hard to fully control in the study. Among women on hormone therapy, higher p-tau217 predicted dementia in those taking combined estrogen and progestin, but not estrogen alone.
The p-tau217 blood test is not yet ready for general population screening. However, this research moves understanding of dementia's early development forward and highlights potential windows for intervention. High p-tau217 levels don't always lead to dementia, suggesting areas for future research. Identifying at-risk women decades before symptoms appear opens the door to earlier prevention and targeted monitoring.