Creator: Help Dementia Editorial Team
Published: 2026-04-12T02:40:03

Reviewed by the Help Dementia Editorial Team — our editors review every article for accuracy against guidance from the National Institute on Aging, the Alzheimer’s Association, and peer-reviewed sources.

Expert panel sits at the center of this dementia and brain health question.

In August 2024, an international panel of experts published revised diagnostic criteria for Alzheimer’s disease that represent the most significant shift in how neurologists and primary care physicians identify this disease in decades. Rather than waiting for cognitive symptoms to appear—memory loss, confusion, difficulty with familiar tasks—the new criteria enable diagnosis based on biological evidence of Alzheimer’s pathology detected through advanced blood tests and imaging. This fundamental change moves Alzheimer’s diagnosis from the realm of observable symptoms to the realm of measurable biology, much like how doctors now diagnose diabetes through blood glucose levels rather than waiting for obvious complications to emerge. The revision was driven by a critical convergence of scientific progress and therapeutic opportunity.

The FDA approval of the first disease-modifying treatments for Alzheimer’s disease—aducanumab in 2023 and lecanemab in 2024—created an urgent need for earlier and more precise identification of people who could benefit from these drugs. At the same time, blood-based biomarkers have become reliable and accessible enough to enable testing beyond specialized research centers. An international working group of 46 experts from 17 countries spent years refining these new standards, published in the journal *Alzheimer’s & Dementia*, to ensure they reflect current scientific evidence and serve patients across different healthcare settings and countries. What this means in practical terms is that a person with early memory concerns might now receive an Alzheimer’s diagnosis before their cognitive decline becomes apparent to family members or affects their ability to work. This earlier identification creates the possibility of starting treatment sooner, when interventions may be most effective—but it also raises important questions about how to counsel people diagnosed with a disease they may not yet experience as a significant problem.

What Changed in How Doctors Diagnose Alzheimer’s Disease?
Understanding Core 1 and Core 2 Biomarkers
How Blood Tests Are Making Early Detection More Accessible
Comparing the Old and New Approaches to Diagnosis
Important Limitations and Implementation Challenges
The International Consensus Behind These Standards
What’s Next: The 2025 Clinical Practice Guidelines and Beyond
Conclusion

What Changed in How Doctors Diagnose Alzheimer’s Disease?

The old diagnostic approach relied heavily on cognitive testing and clinical observation. A person would visit a neurologist, undergo memory assessments, and receive an Alzheimer’s diagnosis if cognitive decline met certain thresholds. Brain imaging like MRI or PET scans could provide supporting evidence, but these were expensive and often reserved for specialists in academic medical centers. The diagnosis required the presence of symptoms—you couldn’t be said to have Alzheimer’s disease unless you already showed signs of cognitive impairment. The revised criteria fundamentally invert this logic. Now, an Alzheimer’s diagnosis can be made on biological grounds alone, in the absence of cognitive symptoms.

A person with normal thinking and memory but who tests positive for Alzheimer’s pathology biomarkers—specifically, amyloid and tau accumulation in the brain—can be diagnosed with presymptomatic Alzheimer’s disease. This represents a conceptual leap similar to diagnosing type 2 diabetes based on blood glucose and insulin resistance before a person develops diabetic complications. The new framework also incorporates neurodegeneration biomarkers that indicate actual brain damage, providing a more complete picture of disease progression. The criteria explicitly acknowledge that not everyone with Alzheimer’s pathology will develop dementia in their lifetime, a limitation that clinicians and patients must understand. However, the presence of this pathology, particularly when combined with cognitive decline or neurodegeneration markers, substantially increases risk and can guide treatment decisions. This shift enables earlier intervention but requires careful counseling so that people understand what a presymptomatic diagnosis means for their individual future.

What Changed in How Doctors Diagnose Alzheimer's Disease?

Understanding Core 1 and Core 2 Biomarkers

The revised criteria introduce a two-tier biomarker classification system designed to improve diagnostic accuracy and clarity. Core 1 biomarkers—amyloid and phosphorylated tau—are considered “early-changing” markers that appear in the brain years or decades before cognitive symptoms. Their presence alone is sufficient to confirm biological Alzheimer’s disease. Core 2 biomarkers—measures of neurodegeneration like phosphorylated tau variants, plasma phosphorylated tau181, and imaging evidence of brain atrophy—are “later-changing” markers that typically appear as brain damage begins. This tiered approach allows clinicians to match the intensity and specificity of testing to the clinical situation. For someone with cognitive symptoms but uncertain diagnosis, testing might start with blood-based biomarkers (which are less expensive and invasive than PET imaging) to look for Core 1 pathology. If present, this confirms Alzheimer’s disease.

If cognitive decline is more advanced, clinicians might look for Core 2 biomarkers to stage the severity and guide treatment urgency. A person with only Core 1 evidence but no cognitive symptoms sits in a presymptomatic category that may warrant different counseling and monitoring strategies than someone showing signs of cognitive decline. One important limitation is that these biomarkers don’t tell the full story of individual risk. Some people with significant amyloid and tau pathology never develop dementia during their lifetime, while others progress rapidly. The presence of biomarkers increases risk substantially, but cannot predict with certainty whether an individual will develop symptoms or when. This uncertainty must be acknowledged in clinical conversations, and patients need realistic information about what these test results mean for their personal future. Additionally, access to these biomarkers remains unequal—blood tests are increasingly available, but some specialized tests and the interpretation of complex results still require neurology expertise that is concentrated in urban centers and academic medical centers.

How Blood Tests Are Making Early Detection More Accessible

One of the most transformative aspects of the revised criteria is the central role of blood-based biomarkers. These tests measure specific proteins—amyloid-beta, phosphorylated tau at various sites, and other neurological markers—that leak from the brain into the bloodstream as pathology develops. A simple blood draw, potentially done at a primary care office, can now provide information that previously required expensive PET imaging or invasive cerebrospinal fluid sampling. Consider a practical scenario: a 58-year-old woman notices she’s been more forgetful lately, struggling to recall names of colleagues she’s known for years. She schedules an appointment with her primary care doctor, who might once have dismissed her concerns as normal aging or recommended a specialist visit. Under the new criteria, that doctor can order a blood test for phosphorylated tau and amyloid biomarkers. If results come back positive, it indicates Alzheimer’s pathology is accumulating in her brain.

This same woman might have had normal results on standard cognitive screening tests, yet the biomarker evidence shows genuine biological disease. She and her doctor can then discuss whether early treatment makes sense for her situation. The accessibility advantage is significant, but it also brings new challenges. Primary care physicians—who may not have extensive neurology training—now need to understand how to order these tests appropriately, interpret results, and counsel patients about presymptomatic disease. Testing at scale requires robust quality control and standardization to ensure that a biomarker test performed in a rural clinic means the same thing as one done in a major medical center. Some blood-based biomarkers are more standardized and reliable than others, and guidance about which tests to use is still evolving. Clinicians also need to recognize that a positive biomarker result doesn’t automatically mean a patient needs immediate treatment—context, age, other health factors, and individual preferences all matter.

How Blood Tests Are Making Early Detection More Accessible

Comparing the Old and New Approaches to Diagnosis

The practical differences between symptom-based and biomarker-based diagnosis are profound, and understanding them helps families and patients navigate the changing landscape of Alzheimer’s care. Under the previous framework, diagnosis typically occurred after cognitive decline became noticeable enough for multiple family members to worry or for it to affect job performance or daily functioning. Treatment, when available, started relatively late in the disease process—potentially after years of silent brain damage. The new biomarker-focused approach enables diagnosis and treatment to begin years or even decades earlier, during the presymptomatic phase when the brain’s compensatory mechanisms may still be relatively intact. For someone at genuinely high risk—particularly those carrying the apolipoprotein E4 (APOE4) gene variant or those with a strong family history of dementia—this earlier intervention represents a meaningful opportunity.

However, this comes with a tradeoff: more people receive an Alzheimer’s diagnosis while still cognitively healthy, which raises psychological and practical challenges. A 50-year-old diagnosed with presymptomatic Alzheimer’s based on biomarkers may face discrimination in employment or insurance, may experience anxiety about their future, or may feel compelled to make major life decisions on the basis of a disease they may not develop for many years. The old approach had the advantage of simplicity and clarity—you had symptoms, therefore you had the disease. The new approach is more nuanced and scientifically accurate but requires sophisticated counseling and shared decision-making. Patients need to understand that biomarker positivity is a risk indicator, not a fixed destiny. They also need realistic information about what early treatment can and cannot do, including the fact that stopping cognitive decline before it starts is not yet proven possible with currently available medications.

Important Limitations and Implementation Challenges

While the revised criteria represent genuine scientific progress, several significant limitations must be understood by both clinicians and patients. First, the relationship between biomarkers and actual cognitive decline remains imperfect. Autopsy studies show that a substantial proportion of cognitively normal older adults have significant Alzheimer’s pathology in their brains—yet they maintained normal thinking throughout their lives. This phenomenon, sometimes called “cognitive reserve,” highlights that Alzheimer’s pathology is necessary but not sufficient for dementia. Some people’s brains tolerate substantial amyloid and tau without functional consequence. Second, the current blood-based biomarkers, while advancing rapidly, are not yet perfectly standardized across laboratories and testing platforms.

A phosphorylated tau measurement from one lab may not be directly comparable to the same measurement from another lab, creating potential for misdiagnosis or mismanagement if results are interpreted without understanding these limitations. Clinicians need to know the specific test platform used and its validation data, information that requires ongoing education as testing evolves. Third, there is a genuine risk of overdiagnosis and overtreatment. If biomarker testing becomes routine screening in asymptomatic populations, many people with low risk of ever developing dementia could be identified as having Alzheimer’s disease, leading to unnecessary anxiety and potentially to treatment with medications that carry side effects. The medications approved for early-stage Alzheimer’s (like lecanemab) can cause amyloid-related imaging abnormalities (ARIA)—brain swelling or microhemorrhages—that in rare cases can be serious. For someone unlikely to develop cognitive symptoms anyway, these risks may outweigh benefits. Clinicians must resist the temptation to test and treat everyone with biomarker evidence and instead focus on those at higher risk based on age, symptoms, genetics, or family history.

Important Limitations and Implementation Challenges

The International Consensus Behind These Standards

The strength of the revised diagnostic criteria rests on the breadth of international expert consensus that developed them. The 46 experts from 17 countries represented diverse healthcare systems, research traditions, and clinical perspectives. This diversity was essential because Alzheimer’s diagnostic and treatment approaches differ substantially across countries.

In the United States, specialists typically have earlier access to advanced imaging and biomarker testing, while in many European and lower-income countries, diagnosis often relies more heavily on cognitive assessment and simple laboratory tests. By involving experts from multiple regions, the workgroup ensured that the revised criteria could be adapted to different healthcare settings and resource levels. The criteria include recommendations for diagnosis in settings with access to advanced biomarking but also acknowledge pathways for diagnosis in resource-limited settings where such testing isn’t available. This international perspective also enriched the discussion of ethical implications—how presymptomatic diagnosis should be counseled, how to avoid genetic discrimination, and how to ensure equitable access to new treatments across different populations and countries.

What’s Next: The 2025 Clinical Practice Guidelines and Beyond

Building on the revised diagnostic criteria, the Alzheimer’s Association released updated clinical practice guidelines in 2025 that provide concrete recommendations for diagnostic evaluation, biomarker testing, patient counseling, and disclosure of suspected Alzheimer’s disease. These guidelines translate the revised criteria into actionable steps that clinicians can follow in real-world settings, including recommendations for which patients should be tested, in what sequence, and how to discuss results with patients and families. The field is moving toward a future where Alzheimer’s disease diagnosis becomes increasingly based on biology and happens earlier in the disease course, ideally before cognitive symptoms emerge.

This shift opens the possibility of treating people while their brains are still more resilient, potentially preventing or substantially delaying the onset of dementia. However, realizing this potential requires not just better diagnostic tests, but also improved treatments—the currently available medications slow cognitive decline modestly but don’t stop it. Ongoing research is focused on combination therapies, treatments targeting tau pathology, and approaches to enhance brain resilience. As these develop, the early diagnostic capability provided by the new criteria will become increasingly valuable.

Conclusion

The standardization of Alzheimer’s diagnostic criteria by international expert panels represents a watershed moment in how we understand and approach this disease. The shift from symptom-based to biomarker-based diagnosis, enabled by advances in blood testing and driven by the availability of disease-modifying treatments, fundamentally changes when and how people receive an Alzheimer’s diagnosis. For individuals and families, this means the possibility of earlier awareness of disease risk and earlier access to treatments that might slow progression. At the same time, this change creates new responsibilities for clinicians, patients, and healthcare systems.

Testing should be thoughtful and targeted rather than routine screening of all older adults. Results must be communicated with nuance and honesty about what biomarkers do and do not predict. Patients need realistic expectations about what early treatment can accomplish and clear information about potential risks and side effects. As these new criteria are implemented across diverse healthcare settings, success will depend on education, shared decision-making, and commitment to equitable access. For anyone concerned about cognitive health or family history of dementia, now is a good time to discuss with a primary care doctor whether biomarker testing makes sense for their individual situation.