Biomarker Testing for Alzheimer Disease: Inside the Latest P-Tau217 Data

Blood-based biomarker testing for Alzheimer disease pathology continues to advance, with recent data evaluating the rule-in performance of plasma phosphorylated tau 217 (P-tau217) blood tests for identifying cognitively unimpaired individuals with Alzheimer disease. Eli Lilly presented findings at the 2026 Alzheimer's Association International Conference (AAIC) showing that P-tau217 blood tests were noninferior to amyloid positron emission tomography (PET) quantitation for detecting early disease pathology.¹ Although P-tau217 blood tests currently remain indicated only for early symptomatic Alzheimer disease, ongoing research into disease-modifying treatments in cognitively unimpaired stages underscored the growing clinical relevance of earlier, noninvasive detection. A recent study in JAMA further supported the prognostic value of P-tau217, reporting that participants with very high P-tau217 levels had a 38% absolute risk of progression to cognitive impairment over 5 years, compared with 24% among those with high levels.² Nino Sireci, MD, discussed these findings and their implications with Psychiatric Times.

Psychiatric Times: What are the clinical highlights and overall results of the recent investigation into P-tau 217 testing?

Nino Sireci, MD: Essentially,P-tau217 blood tests have proven to be highly accurate in confirming Alzheimer disease (AD) pathology to support a diagnosis of AD in symptomatic patients and may help guide management discussions. To further validate this, the data Eli Lilly and Company presented at AAIC evaluated the rule-in performance of P-tau217 blood tests for identifying cognitively unimpaired individuals with AD and assessed whether these tests were noninferior relative to amyloid PET quantitation in detecting early disease pathology.

This is important because cognitively unimpaired AD is characterized by AD pathology in individuals without objective cognitive impairment. Although P-tau217 blood tests are only available for use in early symptomatic AD patients at this time, studies evaluating the impact of disease-modifying treatments in cognitively unimpaired stages of AD are ongoing and, if successful, will make accurate and early identification of AD pathology in this population critical. In independent cohorts, P-tau217 blood tests demonstrated strong rule-in performance and noninferiority to amyloid PET quantitation for identifying AD pathology in individuals with cognitively unimpaired AD.

The results were consistent across 2 independent cohorts (Bio-Hermes and pooled Lilly studies), different assay platforms, and multiple sensitivity analyses, including varying amyloid thresholds and prevalence assumptions. Together, this supports the reproducibility and robustness of P-tau217 performance.

PT: Why is a biomarker test in non-cognitively impaired patients an important development?

Sireci: This is a forward-looking study designed to help build a foundation of data as the AD community looks to better understand earlier stages of AD. Amyloid can begin accumulating in the brain up to 20 years before symptoms appear, creating a long window where disease biology is present but not yet visible clinically. These data showed that P-tau217 blood testing is a promising method to identify underlying pathology in that window, once tests for this population are available and indicated for these uses.

This scientific opportunity also aligns with patient interest, as nearly 4 in 5 Americans (79%) would want to know if they had Alzheimer disease before symptoms emerge or interfere with daily activities, demonstrating the critical importance of early detection.

PT: Biologically, how does testing for P-tau217 enable identification of AD pathology?

Sireci: At the biological level,P-tau217 is a biomarker that reliably detects AD pathology by reflecting the phosphorylated tau present in amyloid plaques and tau tangles, which are the hallmark neuropathological features of AD.

This biological signal is supported by a strong body of evidence, as the presence of P-tau217 in blood correlates with amyloid burden on PET scans and in cerebrospinal fluid. A recently published JAMA study demonstrated that P-tau217 was not only a marker of AD pathology, but also a strong predictor of future clinical progression. In a pooled multicohort analysis, participants with very high P-tau217 levels (>2.5 SD) demonstrated a 38% absolute risk of progression to cognitive impairment over 5 years, compared to 24% for those with high P-tau217 levels (1.1-2.4 SD). While risk estimates were markedly higher over 10 years, longer-term estimates were constrained by limited follow-up data.

Together with Lilly’s data showing noninferiority to amyloid PET for identifying pathology, this reinforces P-tau217 as a clinically meaningful and scalable biomarker that may be capable of both identifying disease biology and informing how it may progress in the earliest stages of AD once tests are available and indicated for these uses.

Lilly is actively investigating the benefits of intervening at the earliest stages of Alzheimer disease. Lilly’s landmark phase 3 TRAILBLAZER-ALZ 3 study enrolled participants who were cognitively unimpaired but identified as having Alzheimer disease pathology using a P-tau217 blood test, which was used in the clinical trial but is not yet available for asymptomatic individuals. P-tau217 was used for study eligibility because of its strong ability to predict underlying Alzheimer disease pathology in cognitively unimpaired individuals.

PT: In a clinical setting, how would these types of tests ideally be used in the course of diagnosis and treatment?

Sireci: Today, FDA-cleared and CE-marked P-tau217 blood tests are only available for use in early symptomatic AD patients, where they can help streamline diagnostic pathways and guide management discussions.

What is particularly encouraging is as P-tau217 blood testing gains broader clinical acceptance and adoption, translating these advances into everyday clinical practice is crucial for identifying early symptomatic AD. P-tau217 blood testing gives clinicians a practical, noninvasive tool to start conversations with symptomatic patients, helping to identify disease earlier in its progression when intervention, planning, and care coordination can have the greatest impact.

Ultimately, in an ideal world, a simple blood sample could be collected at any doctor's office, even in rural or underserved communities, and sent to a major reference lab where, combined with the patient's initial cognitive and clinical assessments, it could provide information to help the treating physician appropriately diagnose and manage patients.

Of course, testing is just one part of the process, and physicians should conduct cognitive assessments on patients 65 and over regularly and educate on signs and symptoms, as well as AD risk factors.

PT: How can biomarker tests like this one work to fill gaps in AD diagnosis and treatment?

Sireci: One reason these tools matter is that despite growing disease awareness, a significant portion of adults with symptoms remain undiagnosed, particularly those in milder disease stages when symptoms are often mistaken for normal aging. Better detection and diagnostic tools help get ahead of disease progression.

That is especially important because there are amyloid-targeting therapies that have been FDA-approved to help slow clinical decline in early symptomatic AD, and data show they have the greatest potential benefit when patients are treated earlier in the disease.

More broadly, greater education, earlier screenings, and increased collaboration within the healthcare system will improve outcomes. P-tau217 blood testing can help to make detection more accessible across diverse populations and healthcare settings without requiring specialized neuroimaging infrastructure.

PT: For the practicing psychiatric clinician, what should they keep in mind around Alzheimer biomarkers testing?

Sireci: One key takeaway is that these results support the potential role of P-tau217 blood tests for identifying AD pathology in individuals with cognitively unimpaired AD who are at risk of clinical progression, and therefore selecting patients who may benefit from secondary prevention strategies.

Another important part is that P-tau217 blood tests are cost-effective, and easy-to-implement diagnostic tools for assessing AD pathology, that were shown to be noninferior to amyloid PET. At the end of the day, better detection and diagnostic tools help get ahead of disease progression, which provides the opportunity to have better outcomes.

Dr Sireci is the senior vice president of clinical biomarker and diagnostic development at Eli Lilly.

References

1. Lilly to present Alzheimer disease diagnostic and therapeutic research at AAIC 2026, including new data on P-tau217 blood tests and amyloid-targeting treatment. Press release. Published July 9, 2026. Accessed August 20, 2026. https://www.prnewswire.com/news-releases/lilly-to-present-alzheimers-disease-diagnostic-and-therapeutic-research-at-aaic-2026-including-new-data-on-p-tau217-blood-tests-and-amyloid-targeting-treatment-302821844.html

2. Buckley RF, Townsend DL, Birkenbihl CJ, et al. Prognostic value of blood-based P-tau217 levels for progression to cognitive impairment. JAMA. 2026.