🎗️ Before Memory Loss: The Alzheimer's Sign That Appears In The Blood

A simple blood test can reveal signs of Alzheimer's risk before memory begins to fail. In a group of nearly 2,700 initially healthy older adults, elevated levels of a protein linked to the disease were associated with a higher likelihood of developing cognitive impairment years later. This discovery could pave the way for a new generation of tests capable of identifying changes long before the first symptoms appear.

Alzheimer's disease can begin causing brain changes many years before memory or other cognitive abilities show clear signs of impairment. Now, a large study suggests that a simple blood test could help identify individuals at higher risk of developing cognitive problems in the future.

The marker analyzed is a specific form of the tau protein, known as phosphorylated tau 217, found in the blood. This protein is linked to the brain changes characteristic of Alzheimer's disease and can rise before symptoms become apparent.

To investigate this possibility, researchers gathered data on 2,684 older adults who showed no cognitive impairment at the start of the study. The participants were drawn from six different studies conducted in North America, Japan, and Australia. Follow-up began as early as 2004, with the most recent assessments taking place in 2025.

Researchers measured the amount of phosphorylated tau-217 in the blood at baseline and then followed the participants for years, tracking who developed cognitive impairment. In total, there were 478 cases of progression over a mean follow-up period of 5.4 years, with some individuals followed for up to 13.5 years.

Differences among participants were primarily observed in the amount of phosphorylated tau-217 present in the blood. The higher the level of this protein at the start of the study, the greater the risk of the individual subsequently developing cognitive impairment. For every one-standard-deviation increase in protein levels, the risk of progression rose by approximately 38%. This association remained significant even when researchers accounted for other indicators of Alzheimer's disease obtained through imaging tests.

The researchers also categorized participants based on protein levels. Among those with elevated levels, the estimated risk of developing cognitive impairment within five years was approximately 24%. For those with very high levels, exceeding 2.5 standard deviations, the risk reached 38% over the same five-year period.

The estimated risk rose further when considering a ten-year timeframe, although the researchers themselves note that these long-term estimates are less precise due to the smaller number of participants available for follow-up over such an extended period.

The test also appeared to be linked to the rate of cognitive decline. Individuals with very high levels of phosphorylated tau 217 showed a more rapid decline in measures of memory and other cognitive abilities during the follow-up period. This is significant because it suggests that the marker is not only associated with the potential to develop cognitive changes but may also help identify individuals at higher risk of experiencing a faster progression.

Despite the promising results, there is a significant difference between indicating risk and predicting a person's future with certainty. The participants belonged to selected groups from aging and Alzheimer's research studies; therefore, the findings still need to be confirmed in more diverse populations that are representative of the general public.

Thus, the phosphorylated tau-217 test should not yet be interpreted as a verdict or a confirmation that someone will develop Alzheimer's. What the study demonstrates is that a blood-detectable marker can provide important information regarding the future risk of cognitive decline, paving the way for monitoring strategies and, eventually, earlier interventions.

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Prognostic Value of Blood-Based P-Tau217 Levels for Progression to Cognitive Impairment

Rachel F. Buckley, Diana L. Townsend, Colin J. Birkenbihl, Madison Cuppels, Gillian T. Coughlan, Mabel T. Seto, Jane A. Brown, Michael J. Properzi, Merle C. Hoenig, Annie Li, Aaron P. Schultz, Jasmeer Chhatwal, Hyun-Sik Yang, Steven Arnold, Pia Kivisäkk, Bryan D. James, Sid O’Bryant, Robert A. Rissman, Melissa Petersen, Jessica Z. K. Caldwell, Tobey Betthauser, Julie Elisabeth Oomens, Maria Carrigan, Brian Healy, Jorge Garcia Condado, Sterling C. Johnson, Wai-Ying Wendy Yau, Oliver Langford, Michelle Farrell, Rebecca E. Amariglio, Dorene M. Rentz, Kathryn V. Papp, Ron Brookmeyer, Timothy J. Hohman, Michael Donohue, Paul S. Aisen, Keith A. Johnson and Reisa A. Sperling

JAMA. July 14, 2026

DOI: 10.1001/jama.2026.12556

Abstract: 

Blood-based biomarkers for Alzheimer disease, particularly plasma phosphorylated tau 217 (p-tau217), accurately reflect early Alzheimer disease brain pathology in cognitively unimpaired individuals, but estimates of absolute risk of progression to cognitive impairment across multiple cohorts are needed. To estimate absolute risk of progression to cognitive impairment and rates of cognitive decline based on plasma p-tau217 across cognitively unimpaired older adults. Longitudinal cohort study using harmonized data from 2684 cognitively unimpaired older adults (defined within cohort) across 6 observational and clinical trial cohorts based in North America, Japan, and Australia. The earliest enrollment was in 2004, with most recent follow-up in 2025. Baseline plasma p-tau217. The primary outcome was time to progression to cognitive impairment (mild cognitive impairment, dementia, or 2 consecutive global Clinical Dementia Rating scores ≥0.5). The secondary outcome was longitudinal change on the latent Preclinical Alzheimer Cognitive Composite (PACC; higher values indicate better performance). Among the 2684 participants (median [IQR] age, 69.6 [66.2-74.2] years; 1697 [63%] female), there were 478 events of progression to cognitive impairment over a median follow-up of 5.4 years (maximum follow-up of 13.5 years). Each 1-SD increase in baseline p-tau217 level was associated with an increased risk of progression to cognitive impairment (hazard ratio, 1.38 [95% CI, 1.30-1.46]), and the association remained significant after adjustment, including β-amyloid positron emission tomography scan Centiloids (hazard ratio, 1.32 [95% CI, 1.24-1.41]). Participants with high (1.1-2.4 SD) and very high (>2.5 SD) baseline p-tau217 had 24% (95% CI, 20%-28%) and 38% (95% CI, 33%-43%) absolute risk of progression over 5 years, respectively, and risk was markedly higher over 10 years, although longer-term estimates were constrained by limited data. Elevated p-tau217 was also associated with faster cognitive decline based on change in latent PACC score. Among the overall sample, baseline latent PACC scores ranged from −0.8 to 2.7. The 5-year annualized decline for the very high p-tau217 group was −0.07 latent PACC units/y (95% CI, −0.10 to −0.05), relative to 0.03 units/y (95% CI, 0.02-0.04) in the low p-tau217 group. In a pooled sample of multiple selected cohorts of cognitively unimpaired older adults, higher plasma p-tau217 levels were consistently associated with increased risk of clinical progression and accelerated cognitive decline. By providing time-specific absolute risk estimates, these findings support the potential of p-tau217 for prognostic model development, with direct implications for future trial design. Further validation in unselected populations is needed to inform individual prognosis and clinical decision-making in cognitively unimpaired individuals.