A landmark meta-analysis finds plasma biomarkers outperforming traditional methods, opening the door to earlier detection and targeted screening for people with genetic risk or prior brain injury.

Dementia affected over 57 million people globally in 2019, a figure expected to rise to 153 million by 2050. The need for scalable, accessible, and accurate diagnostic tools is more pressing than ever.

Alzheimer’s disease is the most common type of dementia, accounting for 60–70% of dementia cases. With disease-modifying treatments now emerging, timely and accurate diagnosis is essential to ensure individuals are eligible for intervention before the onset of clinical symptoms.

In practice, Alzheimer’s disease is still most often diagnosed based on clinical presentation alone, which can be inaccurate. While PET imaging and CSF analysis offer more definitive evidence, these diagnostic tools are not routinely accessible and are typically performed after symptom onset.

The rise of blood-based biomarkers signals a major shift in Alzheimer’s detection. A simple blood test could replace invasive diagnostics, making early and accurate diagnosis more achievable. This comes just as disease-modifying treatments begin to reshape care.

Global Meta-Analysis Study Strengthens Case for Blood-Based Diagnosis

A landmark meta-analysis published in The Lancet Neurology (Sept 2025) reviewed 113 studies, across 24 countries worldwide, involving nearly 30,000 unique individuals. It represents the most comprehensive evaluation to date of blood-based biomarkers for diagnosing Alzheimer’s disease. The studies spanned from cohort, case-control, cross-sectional, and Randomised Controlled Trial (RCT) design, adding confidence that findings are not limited to one research setting.

The researchers examined five plasma phosphorylated tau (p-tau) biomarkers (p-tau181, p-tau205, p-tau212, p-tau217, p-tau231) which are proteins linked to Alzheimer’s pathology. These were compared against gold-standard diagnostic tests like PET scans and CSF analysis.

Among these, p-tau217 emerged as the most accurate, with a sensitivity of 88.1% and specificity of 88.7%, correctly identifying Alzheimer’s pathology in nearly 9 out of 10 cases. Its performance was strongest in individuals with cognitive impairment, while in asymptomatic individuals accuracy was lower, underscoring both its diagnostic potential today and the challenges of applying it to broad early screening.

While this falls just short of the 90% sensitivity and specificity benchmark proposed by the World Health Organization and the Global CEO Initiative for diagnostic use, several p-tau217 assays came close. This creates a strong potential for clinical implementation.

Why It Matters

Unlike PET and CSF tests, plasma biomarkers are less invasive, more affordable, and easier to scale. They’re well-suited for use in primary care, rural clinics, and even targeted screening programmes. p-tau217 has shown consistent performance across different assays and reference standards, including PET, CSF, and autopsy-confirmed pathology.

If adopted widely, blood-based diagnostics could reduce costs, improve access, and enable earlier intervention.

Implications For Screening:

Phosphorylated tau is a hallmark of Alzheimer’s pathology, and plasma p-tau217 now stands out as the leading candidate for blood-based detection. It opens the door to screening individuals at heightened risk, such as:

• Those with a family history of Alzheimer’s or other neurodegenerative diseases.
• Individuals with a history of traumatic brain injury (TBI), who may be at elevated risk for tau-related neurodegeneration.

Guidelines still advise against routine testing in symptom-free people, but p-tau217’s signal in unimpaired groups suggests it could one day support targeted risk profiling and early intervention.

What’s Next?

The meta-analysis makes one thing clear: what comes next is translation into practice. Yet the authors caution that much of the evidence carries bias and that p-tau217’s accuracy is strongest in symptomatic individuals. Large-scale, real-world studies will be critical, and if they succeed, blood tests could shift Alzheimer’s care toward earlier detection and timelier access to treatment.

The challenge now is turning promising data into actionable pathways for clinicians, while safeguarding patients at risk.

References:

Therriault, J., Brum, W.S., Trudel, L., Macedo, A.C., Bitencourt, F.V., Martins-Pfeifer, C.C., Nakouzi, M., Pola, I., Wong, M., Kac, P.R., Real, A.P., Witherow, C., Karikari, T.K., Moscoso, A., Zimmer, E.R., Schöll, M., Pascoal, T., Benedet, A.L., Ashton, N.J., Schindler, S.E., Zetterberg, H., Blennow, K. and Rosa-Neto, P., 2025. Blood phosphorylated tau for the diagnosis of Alzheimer’s disease: a systematic review and meta-analysis. The Lancet Neurology, 24(9), pp.740-752. doi:10.1016/S1474-4422(25)00227-3.

GBD 2019 Dementia Forecasting Collaborators, 2022. Estimation of the global prevalence of dementia in 2019 and forecasted prevalence in 2050: an analysis for the Global Burden of Disease Study 2019. The Lancet Public Health, 7(2), pp.e105-e125. doi:10.1016/S2468-2667(21)00249-8.

World Health Organization (WHO), 2025. Dementia. [online] Available at: https://www.who.int/en/news-room/fact-sheets/detail/dementia [Accessed 11 September 2025].

Livingston, G., et al., 2024. Dementia prevention, intervention, and care: 2024 report of the Lancet Standing Commission. The Lancet, 404(10452), pp.572-628.