Yes, there are several tests for Alzheimer’s disease, and the options have expanded significantly in recent years. For decades, a definitive diagnosis was only possible after death through autopsy. Today, doctors can identify Alzheimer’s biology in living patients using brain scans, spinal fluid analysis, and, most recently, a blood test. The first blood test for Alzheimer’s received FDA clearance in 2025, making biological diagnosis more accessible than ever before.
How Alzheimer’s Is Diagnosed Now
The diagnostic landscape shifted dramatically in 2024 when the National Institute on Aging and the Alzheimer’s Association redefined the disease. Alzheimer’s is now defined by its biology, not its symptoms. That means specific protein changes in the brain (the buildup of amyloid plaques and tangled tau proteins) are what make it Alzheimer’s, regardless of whether memory loss has appeared yet. This biological definition exists because symptoms alone aren’t reliable. Several other conditions, including Lewy body dementia and vascular dementia, can look nearly identical in their early stages.
In practice, most diagnostic workups still begin the traditional way: a doctor evaluates your memory, thinking skills, and daily functioning, then orders tests to confirm whether Alzheimer’s biology is present and to rule out other causes.
Cognitive Screening Tests
The first step is usually a brief cognitive screening in a doctor’s office. The two most common are the Montreal Cognitive Assessment (MoCA) and the Mini-Mental State Examination (MMSE). These take about 10 to 15 minutes and test memory, attention, language, and spatial reasoning. On the MoCA, a score below 26 out of 30 is the standard threshold suggesting mild cognitive impairment, while a score around 18 or below may point toward Alzheimer’s-level decline.
These tests don’t diagnose Alzheimer’s on their own. They measure how well your brain is performing right now, not why it’s struggling. A low score could reflect Alzheimer’s, another form of dementia, depression, medication side effects, or even a thyroid problem. But they’re a useful starting point that helps determine whether further testing is needed.
Brain Imaging: MRI and PET Scans
Most people with suspected dementia will get a brain scan. A standard MRI or CT scan is typically ordered first, mainly to rule out other causes like a stroke, tumor, or fluid buildup. But MRI also reveals patterns of brain shrinkage that can support an Alzheimer’s diagnosis. Doctors look specifically at the hippocampus, the brain’s memory center, and rate its size on a 0-to-4 atrophy scale. Greater shrinkage in this area predicts a higher likelihood of progressing from mild memory problems to full Alzheimer’s dementia.
More specialized PET scans go further by detecting the proteins that define Alzheimer’s. An amyloid PET scan shows whether sticky amyloid plaques have accumulated in the brain. This scan is most useful when a doctor suspects Alzheimer’s but isn’t certain, and a positive or negative result would change the diagnosis. For people with mild cognitive impairment, a positive amyloid PET indicates they likely have early-stage Alzheimer’s and are at greater risk of progressing to dementia. A negative scan, on the other hand, effectively rules out Alzheimer’s as the cause.
A tau PET scan detects the other hallmark protein. While amyloid plaques can appear years before symptoms, tau tangles track much more closely with actual cognitive decline. Where tau shows up in the brain also helps distinguish between typical Alzheimer’s and atypical forms that affect language or vision rather than memory. In current practice, amyloid PET is used more widely for diagnosis, while tau PET adds detail about disease stage and severity.
PET scans are expensive, often costing several thousand dollars. Medicare provides conditional coverage for amyloid PET, but typically only when the scan is part of an approved clinical study or meets specific criteria. Availability is also limited to larger medical centers, which can mean long wait times or travel.
Spinal Fluid Analysis
Cerebrospinal fluid (CSF) testing is another established method. A doctor collects a small sample through a lumbar puncture (spinal tap) and measures levels of amyloid and tau proteins. In Alzheimer’s, amyloid levels in spinal fluid drop (because the protein is getting trapped in brain plaques instead of flowing freely), while tau levels rise.
The test looks at specific ratios between these proteins. For example, on one widely used testing platform, a ratio of phosphorylated tau to amyloid above 0.068 is classified as abnormal and consistent with Alzheimer’s pathology. These ratios agree closely with what amyloid PET scans show, making spinal fluid a reliable alternative when PET imaging isn’t available or affordable.
The main barrier is the procedure itself. A spinal tap is invasive, can cause a temporary headache, and isn’t something most people are eager to repeat. That’s one reason the arrival of blood-based testing has generated so much excitement.
The New Blood Test
The FDA cleared the first blood test for diagnosing Alzheimer’s in early 2025. Made by Fujirebio, the Lumipulse test measures the ratio of a specific tau protein fragment (p-tau217) to amyloid in a standard blood draw. It’s approved for adults 55 and older who are already showing signs of cognitive decline.
In validation studies, the blood test detected amyloid plaques with about 82% sensitivity and 86% specificity, and it picked up tau pathology with similar accuracy (83% sensitivity, 83% specificity). That means it correctly identifies most people who have Alzheimer’s biology, and it correctly clears most people who don’t, though it isn’t perfect. Some people will get a result that needs confirmation with a PET scan or spinal fluid test.
What makes this test transformative is access. A blood draw can happen in any doctor’s office, costs far less than a PET scan, and doesn’t require a specialist or a hospital visit. For the millions of people wondering whether their memory problems are normal aging or something more, this lowers the barrier to getting a clear answer.
Genetic Testing: Risk, Not Diagnosis
You may have heard about genetic tests for Alzheimer’s, particularly for the APOE-e4 gene. About 15% to 25% of people carry one copy of this gene variant, and 2% to 5% carry two copies. Carrying APOE-e4 increases your risk of developing Alzheimer’s, but it is not a diagnosis. Many carriers never develop the disease, and many Alzheimer’s patients don’t carry the gene. No gene has been found to directly cause the common form of Alzheimer’s.
Genetic testing can be useful for understanding your personal risk profile, especially if you have a family history. But it cannot tell you whether you have Alzheimer’s or will get it. The biomarker tests described above are what confirm the actual presence of disease biology.
Ruling Out Other Types of Dementia
Part of the diagnostic process involves making sure symptoms aren’t caused by something else. Lewy body dementia, for instance, shares many features with Alzheimer’s but also involves visual hallucinations, changes in alertness, and movement problems like stiffness, shuffling, and balance issues. A specialized dopamine PET scan can help identify Lewy body disease by revealing reduced dopamine activity in the brain, a pattern not seen in Alzheimer’s.
Doctors also look for early physical signs that point away from Alzheimer’s, including changes in facial expression, hand posture, or handwriting. A clinical tool called the Lewy Body composite risk score helps clinicians screen for these features during a standard office visit. Vascular dementia, frontotemporal dementia, and other conditions each have their own diagnostic signatures on imaging and clinical exams.
What Testing Looks Like in Practice
If you or a family member are concerned about memory, the typical path starts with your primary care doctor. They’ll do a cognitive screening, order basic bloodwork to check for reversible causes (thyroid problems, vitamin deficiencies, infections), and likely request a brain MRI. If those results suggest a neurodegenerative cause, the next step is usually a referral to a neurologist or memory specialist who can order biomarker testing: a blood test, spinal fluid analysis, or PET scan depending on what’s available and appropriate.
With the new blood test now on the market, the process is becoming faster and less invasive. In many cases, a blood draw combined with cognitive testing and an MRI can provide enough information for a confident diagnosis without ever needing a PET scan or spinal tap. For ambiguous results, those more specialized tests remain available as confirmation.