If you notice a loved one starting to have thinking or memory problems, you might wonder: How is Alzheimer’s disease diagnosed? In previous years, the answer wasn’t so simple. But today, thanks to improved technology and new research, getting an early and accurate diagnosis is more possible than ever.

There’s no one test that can determine an Alzheimer’s diagnosis. Instead, doctors use a mix of memory tests, brain scans, and blood tests. Early diagnosis can help you plan treatment sooner, plan for care, and even join clinical trials to test new treatments. In this article, we’ll cover what you need to know about the latest tests for diagnosing Alzheimer’s disease.

How Is Alzheimer’s Diagnosed?

In Alzheimer’s disease, two proteins — beta-amyloid and tau — build up in the brain. Beta-amyloid forms sticky clumps called plaques between brain cells. Tau forms twisted strands known as tangles inside brain cells. These plaques and tangles disrupt brain function and contribute to the memory and thinking problems seen in Alzheimer’s. Tracking these proteins helps doctors diagnose Alzheimer’s early and accurately.

In 2024, the guidelines for diagnosing Alzheimer’s were updated. Previously, a definitive diagnosis for Alzheimer’s could only be made after death. Now, doctors rely on biomarkers — biological signs of disease in the body — to confirm a diagnosis while a person is still alive. Biomarkers for Alzheimer’s are grouped into two main types.

Core 1 biomarkers are the earliest and most important signs. They directly measure amyloid plaques or changes in tau protein using:

• Positron-emission tomography (PET) scans that detect amyloid levels
• Cerebrospinal fluid (CSF) tests that look at the fluid in your brain and spinal cord
• Highly accurate blood tests

Researchers and doctors now agree that an abnormal Core 1 biomarker result is enough to diagnose Alzheimer’s disease.

Core 2 biomarkers appear later in the disease. They measure how much tau has built up and can show how far the disease has progressed. Core 2 biomarkers can be measured using tau PET scans and CSF and blood tests. They aren’t used alone to diagnose Alzheimer’s, but they provide important information about how the disease is progressing.

In addition to looking for biomarkers, doctors use a mix of neuropsychological (mental) tests, imaging scans, and lab tests to diagnose Alzheimer’s.

Medical History and Physical Exam

During an initial evaluation, a doctor will start by asking about your symptoms and reviewing your medical history, including any medications you take. The goal of a physical exam is to check your overall health. Be prepared for questions about:

• Memory or thinking changes
• Family history of Alzheimer’s disease or dementia
• History of head injuries or other health problems
• Medications that could cause neurological (thinking) side effects

Mental Status Tests

After a physical exam, the doctor will perform a neurological exam. This is to check your balance, reflexes, coordination, and senses. The results can help rule out other causes of memory or thinking problems.

This could be accompanied by a series of tests that assess your neuropsychological function — your mental skills, including memory, attention, language, and problem-solving abilities. You might be asked to remember a list of words, name objects, or perform simple calculations. These tests can help spot early signs of cognitive impairment (thinking problems) and track changes over time.

Imaging Scans for Alzheimer’s Disease

Brain imaging helps doctors see changes in the brain linked to Alzheimer’s disease. There are several types commonly used:

• Magnetic resonance imaging (MRI) shows structural (shape) brain changes and any signs of brain shrinkage or injury.
• Computed tomography, or CT scan, helps identify strokes, tumors, or injuries.
• PET scans show areas of low brain activity and areas with beta-amyloid buildup.

A PET scan for Alzheimer’s diagnosis can be particularly helpful. A special type of PET scan uses a drug called flortaucipir F18 (Tauvid). Approved by the U.S. Food and Drug Administration (FDA) in 2020, Tauvid helps detect tau tangles — a major hallmark of Alzheimer’s disease.

Blood Tests for Alzheimer’s Disease

Blood tests have become a game changer in Alzheimer’s diagnosis. New tests can detect key proteins, like beta-amyloid and tau, linked to the disease. One important test measures a protein called MTBR-tau243. Levels of this protein stay normal in healthy people but rise in those with Alzheimer’s, especially as the disease advances. Researchers found that levels of MTBR-tau243 in the blood can show the amount of tau tangles in the brain with accuracy as high as 92 percent. It can also estimate how far Alzheimer’s has progressed.

Other blood tests measure p-tau217, a form of tau protein that helps diagnose Alzheimer’s earlier in the disease. Together, these tests can help doctors confirm Alzheimer’s as well as determine if symptoms are caused by another condition. Blood tests make diagnosis more accessible and may soon help guide personalized treatment plans.

Cerebrospinal Fluid Tests

CSF is the fluid that surrounds the brain and spinal cord. Collecting a small sample involves a procedure called a lumbar puncture or spinal tap. During the test, a doctor inserts a thin needle into the lower back to remove a small amount of fluid. The fluid is then tested for important biomarkers.

Doctors look for two main changes in the CSF: lower levels of beta-amyloid and higher levels of tau proteins. Low beta-amyloid levels suggest that plaques are forming in the brain. High tau levels are a marker for brain cell damage. Together, these findings can confirm the presence of Alzheimer’s disease, even before severe symptoms appear. CSF testing is highly accurate and helps doctors make an early and confident diagnosis.

Ruling Out Other Conditions

Alzheimer’s accounts for the majority of dementia cases — about 80 percent. However, to get an accurate diagnosis, it’s important for doctors to carefully rule out other conditions. This process is also known as differential diagnosis. Some types of dementia can have similar symptoms to Alzheimer’s, such as:

• Lewy body dementia
• Frontotemporal dementia
• Mixed dementia
• Vascular dementia

Accurate diagnosis matters because treatments and support services vary depending on the type of dementia or disease. Other conditions considered in Alzheimer’s differential diagnosis may include:

• Parkinson’s disease
• Huntington’s disease
• Creutzfeldt–Jakob disease
• Korsakoff syndrome
• Normal pressure hydrocephalus

Staging of Alzheimer’s Disease

After confirming a diagnosis, doctors may stage the disease. Staging allows doctors to describe how advanced the disease is. Staging for Alzheimer’s mainly involves how much amyloid and tau have built up and whether there is neurodegeneration (brain shrinkage).

Doctors use brain scans, like PET scans, or CSF and blood tests to determine the stage. For Alzheimer’s disease, there are four stages:

• Stage A — Early amyloid buildup
• Stage B — Amyloid buildup and early tau changes
• Stage C — Amyloid buildup and tau changes with moderate brain changes
• Stage D — Amyloid buildup and tau changes with advanced brain changes

Staging is an important part of understanding how fast the disease may progress and deciding what treatments may work best.

Why Early and Accurate Diagnosis Matters

Getting an early and accurate diagnosis of Alzheimer’s is crucial. It helps doctors develop a plan of treatment and implement it sooner, when they may be most effective. It also gives you and your family time to plan for the future, make informed decisions, and find the right support services. As new therapies become available, knowing exactly how advanced someone’s disease is could help doctors personalize treatment plans and greatly improve outcomes.

Organizations like the Alzheimer’s Association and the National Institute on Aging offer resources and support for families and caregivers. If you or a loved one notices signs of Alzheimer’s disease, talk to your doctor. Early intervention can make a difference.

Talk With Others Who Understand

On myALZteam, the social network for people with Alzheimer’s disease and their loved ones, more than 86,000 members come together to ask questions, give advice, and share their stories with others who understand life with Alzheimer’s disease.

What has the path to Alzheimer’s disease diagnosis looked like for you or your loved one? Share your experience in the comments below, or start a conversation by posting on your Activities page.