Alzheimer's Diagnosis Gets a Major Overhaul with New Criteria

The Alzheimer's Diagnosis That No Longer Depends on Memory Loss

For decades, the only way to get an Alzheimer's diagnosis was to fail. You forgot your grandchild's name. You got lost on the way home from the grocery store. A doctor ran some cognitive tests, and if you scored badly enough, you received the label. The disease was defined by its symptoms.

That is now obsolete.

In a sweeping revision published in Alzheimer's & Dementia, a workgroup convened by the National Institute on Aging and the Alzheimer's Association has done something radical: They have redefined Alzheimer's disease as a biological process, not a clinical one (Jack et al., 2024). You can have Alzheimer's pathology in your brain right now, without a single symptom, and the new criteria say you have the disease. This is not a subtle tweak. This is a philosophical shift that changes who gets diagnosed, when they get diagnosed, and what we mean when we say the word "Alzheimer's."

The paper, led by Clifford R. Jack of the Mayo Clinic, carries 2,082 citations and updates a framework that has governed Alzheimer's research since 2018. But this version is different. It is designed as a "bridge between research and clinical care" (Jack et al., 2024). That means your doctor could soon be using these criteria to tell you whether you have Alzheimer's years or even decades before you forget anything at all.

Why Defining Disease by Biology Instead of Symptoms Matters

Medicine has done this before. Oncology does not wait for a tumor to cause pain before calling it cancer. Cardiologists do not wait for a heart attack to diagnose coronary artery disease. But neurology has been stuck in a backward logic: You only have a neurodegenerative disease once you show neurodegenerative symptoms.

Jack and his colleagues argue that this makes no sense. "Defining diseases biologically, rather than based on syndromic presentation, has long been standard in many areas of medicine (e.g., oncology), and is becoming a unifying concept common to all neurodegenerative diseases, not just AD" (Jack et al., 2024). The authors are saying that Alzheimer's should be treated the same way we treat other diseases: You have it if the biology says you have it, regardless of what you feel.

The implications are enormous. Right now, approximately 6.5 million Americans have a clinical Alzheimer's diagnosis. But the number of people with biological Alzheimer's, meaning the amyloid plaques and tau tangles in their brain, is likely much higher. Many of these people will never develop dementia in their lifetime. Others will develop it slowly over 20 years. The new criteria capture all of them under the same disease label.

The Biomarker Revolution That Made This Possible

You cannot redefine a disease without tools to measure it. For Alzheimer's, those tools are biomarkers, and they have gotten dramatically better in the past five years.

The workgroup divides biomarkers into two categories: Core 1 and Core 2. Core 1 biomarkers are the early detectors. They include amyloid PET scans, cerebrospinal fluid tests, and a new class of blood tests that measure phosphorylated tau 217 (p-tau217). These biomarkers "map onto either the amyloid beta or AD tauopathy pathway" but "reflect the presence of ADNPC more generally (i.e., both neuritic plaques and tangles)" (Jack et al., 2024).

What this means in plain English: A single positive blood test can now tell you, with high accuracy, that Alzheimer's pathology is present in your brain. You do not need a spinal tap or an expensive PET scan. You do not need cognitive symptoms. You need a blood draw.

The authors are explicit about the diagnostic power of these tests. "An abnormal Core 1 biomarker result is sufficient to establish a diagnosis of AD and to inform clinical decision making throughout the disease continuum" (Jack et al., 2024). This is the headline: A blood test can diagnose Alzheimer's disease, period.

What the New Diagnostic Criteria Actually Say

The criteria are not a step by step clinical guide. The authors emphasize that they are "general principles to inform diagnosis and staging of AD that reflect current science" (Jack et al., 2024). But the principles themselves are remarkably clear.

The diagnosis now rests on a binary: Is a Core 1 biomarker abnormal or not? If yes, you have Alzheimer's disease. That is the biological diagnosis. The clinical stage, meaning whether you have symptoms and how severe they are, is a separate axis. You can be biologically positive and clinically asymptomatic. You can be biologically positive and have mild cognitive impairment. You can be biologically positive and have full blown dementia. All of these are Alzheimer's disease.

This creates a new staging system that integrates biology and symptoms. The authors describe "an integrated biological and clinical staging scheme" that accounts for the fact that "common copathologies, cognitive reserve, and resistance may modify relationships between clinical and biological AD stages" (Jack et al., 2024). In other words, two people with the same amount of brain pathology can have very different symptoms depending on their age, genetics, other health conditions, and even their education level.

How the Study Was Built

This is not a single experiment. It is a consensus document from a workgroup convened by two of the most powerful organizations in Alzheimer's research. The group included Clifford R. Jack from Mayo Clinic, J. Scott Andrews from the Alzheimer's Association, Thomas G. Beach from Banner Sun Health Research Institute, and Teresa Buracchio from the FDA, among others. They reviewed the explosion of biomarker research since 2018 and synthesized it into a new framework.

The methodology is one of expert consensus grounded in published evidence. The authors do not present new data from a single trial. Instead, they reinterpret the entire field. This gives the document enormous weight because it represents an agreement among leading researchers about how to move forward. But it also means the criteria are only as good as the evidence behind the biomarkers, and that evidence is still accumulating.

The Blood Test That Changes Everything

The most practical consequence of these new criteria is the elevation of blood biomarkers. Five years ago, blood tests for Alzheimer's were research tools with questionable accuracy. Today, they are approaching clinical grade.

The specific biomarker that gets the most attention is phosphorylated tau 217, or p-tau217. This protein fragment appears in the blood when Alzheimer's pathology is active in the brain. The authors list "accurate plasma biomarkers (especially phosphorylated tau 217)" as Core 1 biomarkers that can establish a diagnosis (Jack et al., 2024).

The word "accurate" is doing heavy lifting here. Not all blood tests are created equal. Some measure different forms of amyloid or tau and have varying levels of accuracy. But the p-tau217 tests, particularly those from companies like Roche and Eli Lilly, have shown remarkable performance in research studies, with accuracy rates above 90 percent in distinguishing Alzheimer's from other forms of dementia.

This changes the economics of diagnosis. A PET scan costs thousands of dollars and requires a radioactive tracer. A spinal tap is invasive and requires a specialist. A blood test costs a few hundred dollars and can be done in any clinic. If these criteria become standard, the bottleneck in Alzheimer's diagnosis shifts from "can we afford the test" to "are we ready to tell people the result."

Core 2 Biomarkers and the Staging of Disease

Core 1 biomarkers tell you whether Alzheimer's pathology is present. Core 2 biomarkers tell you how advanced it is. These include tau PET scans and more specialized biofluid tests that measure tau tangles directly.

"Later-changing Core 2 biomarkers (biofluid and tau PET) can provide prognostic information, and when abnormal, will increase confidence that AD is contributing to symptoms" (Jack et al., 2024). This is a crucial distinction. A Core 1 positive result means you have the disease. A Core 2 positive result means the disease is actively causing damage and symptoms are likely to appear or worsen.

This two tier system allows doctors to stratify patients. Someone who is Core 1 positive but Core 2 negative might be in an early, potentially reversible stage. Someone who is positive on both is further along the pathological cascade. This matters enormously for clinical trials testing treatments that aim to prevent or slow the disease. You do not want to enroll people who already have widespread tau tangles in a prevention trial. You want the Core 1 positive, Core 2 negative people.

What This Means for People Who Have No Symptoms

This is the most controversial part of the new criteria. If you are 55 years old, feeling fine, and a blood test shows you have Alzheimer's pathology, the criteria say you have Alzheimer's disease. You are asymptomatic, but you have the disease.

The authors are clear about this: "We define Alzheimer's disease (AD) to be a biological process that begins with the appearance of AD neuropathologic change (ADNPC) while people are asymptomatic" (Jack et al., 2024). The disease starts before the symptoms. The symptoms are a late stage complication, not the disease itself.

This mirrors how we think about other chronic diseases. A person with elevated blood pressure has hypertension even if they feel fine. A person with a growing tumor has cancer even if they have no pain. The difference is that we have effective treatments for hypertension and many cancers. For Alzheimer's, we have drugs like lecanemab and donanemab that modestly slow progression, but we have no cure and no proven prevention strategy.

The criteria are ahead of the treatments. They tell you that you have a disease before you can do much about it. This creates an ethical challenge that the authors acknowledge implicitly by noting that the criteria are "not intended to provide step by step clinical practice guidelines for clinical workflow or specific treatment protocols" (Jack et al., 2024). They are giving you the diagnosis. Your doctor still has to figure out what to do with it.

What the Research Does Not Prove

The new criteria are a framework, not a final answer. Several open questions remain.

First, not everyone with Alzheimer's pathology develops dementia. Autopsy studies have consistently found people who died with abundant plaques and tangles but had normal cognition until the end. The criteria do not explain this disconnect. They simply note that "cognitive reserve, and resistance may modify relationships between clinical and biological AD stages" (Jack et al., 2024). This is a placeholder for something we do not understand.

Second, the accuracy of blood biomarkers varies by age, race, and other health conditions. Most validation studies have been done in predominantly white, well educated populations. It is not clear whether a p-tau217 test performs equally well in a 75 year old Black woman with hypertension and diabetes as it does in a 65 year old white man with no comorbidities. The criteria assume the biomarkers are accurate, but the evidence base is still growing.

Third, the criteria do not address how to handle incidental findings. If a person gets a blood test for something else and the p-tau217 comes back positive, what happens? The authors do not recommend population screening. The criteria are designed for people who present with symptoms or have a strong family history. But as blood tests become cheaper and more available, incidental positives will happen, and the field has no protocol for managing them.

The Practical Upside: Better Clinical Trials and Faster Drug Development

The biggest immediate beneficiary of these criteria is not patients. It is research. Clinical trials for Alzheimer's drugs have been hamstrung by imprecise diagnosis. Up to 30 percent of people enrolled in some trials did not actually have Alzheimer's pathology. They had other forms of dementia or mixed pathology. This diluted the results and made it harder to show that drugs worked.

With biomarker based diagnosis, trials can enroll only people who are Core 1 positive. This increases the signal to noise ratio and reduces the number of patients needed to prove a drug works. It also allows trials to target specific stages of the disease. You can test prevention drugs in Core 1 positive, asymptomatic people. You can test early intervention drugs in Core 1 positive people with mild symptoms. You can test symptomatic treatments in people with advanced Core 2 positivity.

The authors designed the criteria with this in mind. They wanted a framework that "reflects current science" and "serves as a bridge between research and clinical care" (Jack et al., 2024). The bridge goes both ways. Research informs the criteria, and the criteria enable better research.

What This Actually Means

• ▸If you are over 50 and worried about Alzheimer's, a blood test can now tell you with high accuracy whether Alzheimer's pathology is present in your brain. This test is not yet standard in most clinics, but the new criteria clear the path for its adoption.

• ▸A positive blood test does not mean you will develop dementia. Many people with Alzheimer's pathology never lose their memory. The criteria separate the diagnosis (you have the biology) from the prognosis (you may or may not get symptoms).

• ▸Clinical trials for Alzheimer's drugs will become more efficient because they can now enroll only people who actually have the disease. This should accelerate drug development and reduce the cost of testing new treatments.

• ▸If you already have a diagnosis of mild cognitive impairment or dementia, the new criteria may change your label but not your treatment. The criteria are about diagnosis, not about new therapies.

• ▸The biggest ethical question remains unanswered: Should you get tested if you have no symptoms and no family history? The criteria do not answer this. They give you the tool. You and your doctor must decide whether to use it.