Blood Test Shows Promise in Predicting Alzheimer’s Disease Risk Decades in Advance

A simple blood test may facilitate predict a woman’s risk of developing dementia up to 25 years before symptoms appear, according to a new study published on March 10, 2026, in JAMA Network Open. The test measures levels of phosphorylated tau 217 (p-tau217), a protein linked to the brain changes seen in Alzheimer’s disease.

Study Details and Findings

Researchers tested blood samples from approximately 2,800 cognitively healthy women aged 65 to 79. Over a follow-up period of up to 25 years, over 1,300 women developed dementia or mild cognitive impairment (MCI), a potential precursor to dementia.

Women with the highest blood levels of p-tau217 at the start of the study were more than twice as likely to develop dementia or MCI compared to those with the lowest levels. This suggests a strong association between elevated p-tau217 levels and future cognitive decline.

Factors Influencing Risk Prediction

The study revealed that the predictive power of the blood test varied based on several factors:

• Age: Higher p-tau217 levels were more strongly linked to poorer cognitive outcomes in women over 70.
• Genetic Predisposition: The test was a better predictor of dementia risk in women with a genetic predisposition for Alzheimer’s disease.
• Hormone Therapy: Elevated p-tau217 levels were a stronger predictor of dementia risk in women who had used hormone therapy for menopause combining both estrogen and progestin, compared to those who hadn’t.

Hormone Therapy and Cognitive Risk

It’s important to note that the increased risk of cognitive decline associated with hormone therapy in this study was observed in women who initiated hormone therapy after age 65. Experts suggest that starting estrogen therapy earlier in menopause may have a neutral or even beneficial effect on cognition. Current recommendations advise women to consider starting hormone therapy before age 60 or within 10 years of the onset of menopause symptoms to minimize potential health risks Mayo Clinic.

Implications for Dementia Diagnosis and Prevention

Currently, blood tests for p-tau217 are approved by the U.S. Food and Drug Administration (FDA) to diagnose Alzheimer’s disease in individuals 55 and older who are already exhibiting symptoms. But, the potential for early risk prediction is significant.

Researchers emphasize that blood-based biomarker tests are less invasive and potentially more precise than traditional methods like spinal taps or brain scans Nature. While not yet approved for widespread screening, the findings suggest that this blood test could be “game-changing” in the field of dementia risk assessment UC San Diego.

“This is one of the largest studies to demonstrate that p-tau217 blood levels can successfully predict future risk of cognitive impairment and dementia,” says JoAnn Manson, MD, MPH, DrPH, a professor at Harvard Medical School.

Looking Ahead

Further research is needed to refine the employ of p-tau217 blood tests for early dementia risk assessment and to explore potential prevention strategies for individuals identified as being at elevated risk. The development of accessible and accurate blood-based biomarkers represents a significant step forward in the fight against Alzheimer’s disease and related dementias.