Before symptoms: preclinical Alzheimer's

Alzheimer's disease starts in the brain long before anyone notices memory problems. Scientists now think the first changes can begin 20 years or more before symptoms.³ This quiet early period is called preclinical Alzheimer's. "Preclinical" means before a person has any signs a doctor or family member would notice.

You may hear about this stage in the news, in ads for blood tests, or from a friend in a research study. This page explains what it means, why experts disagree about what to call it, and why doctors do not advise testing healthy people outside of research.

What happens in the brain before symptoms

Two proteins are at the center of Alzheimer's disease:

• Amyloid is a sticky protein that clumps into plaques between brain cells.
• Tau is a protein inside brain cells. In Alzheimer's, it twists into tangles that harm the cells.

In the preclinical stage, amyloid slowly builds up first. Tau changes often follow later.¹ The brain can cope with these changes for a long time, so the person feels and acts like themselves.

Much of what we know about timing comes from families with rare genes that almost always cause Alzheimer's. Their symptoms tend to start near the same age as a parent's. In these families, amyloid begins to rise about 19 years, on average, before expected symptoms. Brain shrinkage shows up much later, about 5 years before, on average.³

In most older adults, the timing is far less certain.

Where preclinical fits in the stages

Doctors used to describe Alzheimer's in three broad stages: preclinical, mild cognitive impairment, and dementia.² The 2024 criteria from an Alzheimer's Association workgroup add more detail. The early stages look like this:³

Stage 1 is what most people mean by "preclinical Alzheimer's." A person may stay in stage 1 for many years, or for the rest of their life.³ For the full picture of later stages, see Stages of dementia.

A biomarker is a measurable sign of what is happening in the body, found with a scan or in a body fluid.⁵ For Alzheimer's, the main ones are:

• An amyloid PET scan, a brain scan that uses a small amount of a tracer to light up plaques. See brain scans.
• A spinal fluid test, which measures amyloid and tau in fluid from the lower back. See spinal fluid tests.
• Blood tests, which measure forms of amyloid and tau in a blood sample. See blood tests for Alzheimer's.

The new biology-based definition, in plain words

For many years, a person was diagnosed with Alzheimer's only after symptoms began. In June 2024, an Alzheimer's Association workgroup published new criteria. They define Alzheimer's as a biological disease, much like doctors think about cancer or heart disease before symptoms appear.¹

Under these criteria, one abnormal result on a core test, such as an amyloid PET scan, a spinal fluid test or an accurate blood test, is enough to say Alzheimer's disease is present. That is true even if the person has no symptoms.¹ The authors also stress that the criteria are general principles, not step-by-step rules for doctors' offices.²

Not everyone agrees. In late 2024, an international group of experts (the International Working Group) pushed back. They said most people with positive biomarkers and normal thinking will not develop symptoms anytime soon. Telling them they "have Alzheimer's" could do more harm than good.⁴ This group suggests calling such people at risk for Alzheimer's. They would save the label "presymptomatic Alzheimer's" for people whose test pattern shows symptoms are likely soon.⁴

What this means for you. Both groups agree on the most practical point: amyloid in the brain of a healthy person raises the chance of future memory problems, but it does not decide your future. For now, the Alzheimer's Association says this kind of testing belongs in research, not in regular doctor visits.²

Does amyloid mean you will get dementia?

Not always. Many older people die with amyloid plaques in their brain without ever having memory problems.¹ Some live long enough to develop symptoms, and some die of other causes first. Having stage 1 Alzheimer's does not guarantee dementia.³

Higher levels and more kinds of brain changes seem to raise the odds. In a 2026 study of nearly 2,700 people with normal thinking, average age 70, those with very high levels of a blood marker called p-tau217 had an estimated 78% chance (about 3 in 4) of developing thinking problems within 10 years.¹⁰ People with only slightly raised levels had a lower risk.¹⁰

Even so, the researchers said this one number cannot fully predict a single person's future. Age, genes, kidney health, weight and other factors can affect both the test result and the risk of dementia.¹⁰ The 2026 Facts and Figures report also notes that other health problems can affect biomarker results, and that cutoffs may differ across racial and ethnic groups.³

Many older brains also have more than one problem at once, such as small strokes or other protein changes.¹ See mixed dementia.

Why testing healthy people is not advised outside research

The Alzheimer's Association recommends against testing people who have no thinking problems, unless they are part of a research study.² This is true even under its own new biology-based criteria. Here is why:

1. There is no approved treatment for this stage. Lecanemab (Leqembi) and donanemab (Kisunla) are approved only for people who already have mild symptoms. They were not tested in people at stages 0 to 2.³ As of October 2026, no medicine is approved to prevent Alzheimer's in people without symptoms.²

2. The results are hard to interpret. A positive result does not tell you whether or when symptoms will come.^3,10 A negative result does not mean you will never get dementia from any cause.

3. The blood tests on the market were made for people with symptoms. The first FDA-cleared blood test, cleared in May 2025, is for adults 55 and older with signs of memory decline who are seen in a specialty clinic. The FDA says it is not a screening test.⁷ A second FDA-cleared blood test, for primary care, is also for people with thinking complaints.³ A 2025 Alzheimer's Association guideline on blood tests covers only people with thinking problems seen in specialty care. It also warns that many tests for sale do not meet its accuracy standards.⁸

4. Experts advise against consumer and screening tests. Alzheimer's Association guidance says blood tests should not be used to screen the general public or sold as direct-to-consumer risk tests.⁹

5. A result can be a heavy burden. Learning you have amyloid can bring worry or fear, with no medical treatment to offer. Family members may worry about their own risk too.

6. Insurance protections have gaps. A federal law called GINA protects genetic test results from use in health insurance and most job decisions. It does not cover life, disability or long-term care insurance, and it does not apply to employers with fewer than 15 workers.¹⁵ Amyloid and tau tests are not genetic tests, so GINA may not protect those results at all. Ask before testing who will see the results.

Research studies for people without symptoms

Research is where testing healthy people makes sense. Studies need people at this stage to learn whether treatment can delay or prevent symptoms.

What has been tried so far:

• The A4 study tested a drug called solanezumab in people with amyloid but no symptoms. Results in March 2023 showed it did not slow decline compared with placebo (a look-alike with no medicine).¹¹
• The AHEAD 3-45 study is testing lecanemab in people ages 55 to 80 with no symptoms and raised amyloid. It is no longer enrolling. Main results are expected around the end of 2028.¹²
• The TRAILBLAZER-ALZ 3 study is testing donanemab in people ages 55 to 80 with preclinical Alzheimer's. It is also no longer enrolling. Main results are expected around late 2027.¹³

These dates are estimates and can change.

If you want to help, see joining a dementia clinical trial. The Alzheimer's Association Helpline at 800-272-3900 can also point you to studies near you.

What you can do now, with or without a test

You do not need a biomarker test to protect your brain. A 2024 report from a major international commission named 14 health and lifestyle factors linked to dementia. It estimated that nearly half of dementia cases (about 45%) might be prevented or delayed if all of them were addressed.¹⁴ The factors include high blood pressure, hearing loss, untreated vision loss, high LDL cholesterol, diabetes, smoking, heavy drinking, physical inactivity, depression and social isolation.¹⁴

In the U.S. POINTER study, older adults at risk of memory decline followed a lifestyle program for about two years. It included exercise, the MIND diet, brain and social activities, and health checks. Thinking scores improved in both the structured and self-guided groups, with greater gains in the structured group.¹⁶ The study did not show that the program prevents dementia. That is still being followed.¹⁶

For a fuller plan, see keeping your brain healthy.

Worried about your memory?

If you or your family notice real changes in memory or thinking, that is different from preclinical Alzheimer's. It is a reason to see a doctor. Many causes of memory trouble can be treated, such as thyroid problems, low vitamin B12, medicine side effects, poor sleep or depression. See treatable conditions that look like dementia and the first doctor visit about memory.

If fear about Alzheimer's is taking over your days, read about health anxiety.

Common questions

Should I get an amyloid blood test to see if I will get Alzheimer's?

If you have no memory or thinking problems, experts advise against it outside of research.^2,9 The available tests were made for people with symptoms, and no treatment is approved for people without them.^3,7 If you are curious about your risk, a research study is the best place to learn it with proper support.

My mother had Alzheimer's. Should I be tested?

Most cases of Alzheimer's are not caused by a single gene.⁶ Gene tests are not routinely used to predict dementia. A specialist may order one in special cases, such as early onset with a strong family history.⁵ Read genes and dementia and talk with a doctor or genetic counselor.

I feel my memory is slipping, but tests are normal. What is that?

This is sometimes called subjective cognitive decline. Under the 2024 criteria, a person with mild changes like this plus abnormal biomarkers would be in stage 2.³ But many things cause these feelings, including stress, poor sleep, low mood and normal aging. Mention it to your doctor, and see mild cognitive impairment for what comes next if changes grow.

Education only. This page is general information written from the sources listed. It is not medical, legal or financial advice and does not replace a doctor, therapist or lawyer who knows your situation. How we write and check pages.