Blood Biomarkers Are Rewriting How We Diagnose Alzheimer's Disease
A landmark Lancet review maps the evolving Alzheimer's diagnostic landscape, highlighting how blood biomarkers may soon transform global clinical practice.
Summary
A major 2025 Lancet review by an international team of leading dementia researchers examines the rapidly changing diagnosis of Alzheimer's disease. Before biomarkers existed, definitive diagnosis required post-mortem examination. Today, PET imaging and cerebrospinal fluid analysis can detect β-amyloid and hyperphosphorylated tau — the molecular hallmarks of Alzheimer's — during life, enabling precise differential diagnosis and eligibility assessment for newly approved anti-amyloid therapies. The review highlights that blood-based biomarkers, already available in some countries, represent the next diagnostic revolution. These accessible tests could dramatically change how and where Alzheimer's is diagnosed, potentially shifting burden away from specialist centers and reshaping health systems worldwide.
Detailed Summary
Alzheimer's disease is among the most feared and costly conditions associated with aging, representing a leading cause of disability and social care expenditure globally. For decades, a definitive diagnosis was only possible after death through post-mortem brain examination — a fundamental limitation that impeded both clinical care and therapeutic development.
This first paper in a Lancet Series reviews the current state of Alzheimer's diagnosis in specialist settings. The authors describe how clinicians conduct differential diagnoses to determine whether Alzheimer's pathology — specifically cerebral deposition of β-amyloid plaques and hyperphosphorylated tau tangles — contributes to a patient's cognitive impairment.
The review highlights that PET neuroimaging and cerebrospinal fluid (CSF) analysis now enable molecular-level diagnosis during life. These biomarkers of β-amyloid and tau dysregulation are not merely confirmatory tools; they are now a mandatory gateway for determining eligibility for recently approved anti-amyloid immunotherapies such as lecanemab and donanemab, marking a fundamental shift in clinical practice.
Looking ahead, the authors anticipate that blood-based biomarkers — measuring plasma phosphorylated tau, amyloid ratios, and neurodegeneration markers — will trigger a second diagnostic revolution. Already available in some countries, these tests offer accessibility far beyond what PET or lumbar puncture can provide, potentially enabling diagnosis in primary care and lower-resource settings worldwide.
The review carries important caveats: it is based on a narrative synthesis without a formal systematic review methodology, and the clinical utility of blood biomarkers across diverse populations and health systems remains incompletely validated. Many authors also disclose extensive industry relationships with pharmaceutical companies developing Alzheimer's diagnostics and therapeutics, warranting careful interpretation of the framing and conclusions.
Key Findings
- PET and CSF biomarkers now allow molecular-level Alzheimer's diagnosis during life, replacing post-mortem confirmation.
- Biomarker testing is now mandatory to determine eligibility for approved anti-amyloid therapies like lecanemab.
- Blood-based biomarkers measuring plasma tau and amyloid are already available in some countries and signal a new diagnostic era.
- Accessible blood tests could shift Alzheimer's diagnosis from specialist centers to primary care globally.
- The diagnostic journey in specialist settings centers on differential diagnosis of β-amyloid and tau pathology as contributors to impairment.
Methodology
This is a narrative review article — the first paper in a Lancet Series on Alzheimer's disease — authored by an international panel of 18 leading dementia researchers and clinicians. It synthesizes current evidence on diagnostic practices, biomarker technologies, and clinical workflows in specialist memory settings. No primary data collection or systematic review methodology was employed.
Study Limitations
As a narrative review without systematic methodology, it may reflect the perspectives and framing of its authors, many of whom have extensive financial ties to pharmaceutical companies active in Alzheimer's diagnostics and treatment. Blood biomarker performance data across ethnically and clinically diverse populations remain limited, and widespread clinical implementation varies considerably by country and health system.
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