A blood test that detects a protein linked to Alzheimer’s disease may help predict future cognitive impairment in older adults who are currently symptom-free, according to new research presented on 15 July 2026 at the Alzheimer’s Association International Conference (AAIC) 2026 in London (UK) and online and simultaneously published in JAMA - The Journal of the American Medical Association.
Researchers found that higher levels of the blood biomarker p-tau217 predicted faster cognitive decline, with the strongest effects in study participants with elevated amyloid beta based on a PET scan. Cognitively healthy older adults with very high p-tau217 had an approximately 78% risk of developing cognitive impairment (defined as mild cognitive impairment or MCI, dementia or a consecutive clinical dementia rating or CDR, of 0.5) over ten years, and about a one-in-three chance within five years. Even in those with slightly elevated p-tau217 (just over the average), the absolute risk of cognitive impairment was 15% and 45% over five and ten years, respectively.
The results reported at AAIC 2026 add a new dimension to a test already known to reliably identify Alzheimer’s-related changes in the brain. This study establishes the test’s prognostic value: p-tau217 levels in blood can be used to estimate a person’s risk of developing symptoms years later. This gives Alzheimer’s care a forward-looking risk measure of a type that clinicians already use in other conditions, for example a cholesterol or blood-pressure reading — used not only to diagnose disease, but also to gauge future risk and guide what to do about it.
Researchers analysed data from nearly 2,700 cognitively unimpaired adults, average age 70, from six major Alzheimer’s research groups and clinical trials, making it one of the largest and most comprehensive analyses to date examining the long-term prognostic value of p-tau217. The patients were cognitively healthy when their blood was collected and were followed for an average of nearly five years, with some followed for more than a decade. Researchers tracked participants over time using standard cognitive assessments to measure memory, thinking and daily functioning, then applied statistical models based on those real-world outcomes to estimate the likelihood of cognitive decline over two, five and ten years.
The study found:
Adults with very high p-tau217 levels — more than twice as high as average levels in the study — had a 78% estimated likelihood of progressing to cognitive impairment within ten years and roughly a 38% risk within five years.
People with moderately elevated levels had a lower but still significant risk, with approximately 15% risk over five years and 45% risk over ten years.
In this study, blood test results provided important predictive information beyond brain scans and genetic testing results.
Researchers cautioned that p-tau217 alone cannot fully predict an individual’s future risk — knowing someone’s ptau217 level alone can tell you something, but not everything. Factors including age, genetics, kidney function, obesity and racial and ethnic background can influence biomarker levels and dementia risk. The researchers also noted that more diverse study populations and longer follow-up will be needed to refine long-term estimates.
Full AAIC press release available, here: https://aaic.alz.org/releases-2026/blood-test-p-tau217-predicts-alzheimers-risk.asp
Read the full study in JAMA: https://jamanetwork.com/journals/jama/fullarticle/2851720
