How Alzheimer’s Is Diagnosed — and Why It’s So Often Gotten Wrong

Diagnosing dementia is rarely straightforward. Alzheimer’s, Lewy body dementia, frontotemporal dementia and other neurodegenerative diseases can produce overlapping symptoms, and different diagnostic tools come with different strengths and limitations. As a result, getting the diagnosis right can be difficult, and misdiagnosis is not uncommon. 

That matters because an accurate, early diagnosis can shape everything that comes next, from care planning and support to eligibility for treatments that may slow the progression of Alzheimer’s disease.

Why is an Alzheimer’s diagnosis so hard to get right?

For much of the last century, Alzheimer’s was diagnosed largely through clinical symptoms and by ruling out other possible causes of cognitive decline. Doctors looked for other explanations for memory problems and, when none fit, arrived at a probable Alzheimer’s diagnosis.

“The historical medical practice in the United States has been to take a diagnosis of exclusion,” Marwan Sabbagh, MD, a behavioral neurologist at Barrow Neurological Institute’s Alzheimer’s and Memory Disorders Program, told Being Patient. “You get a thyroid [exam] to exclude thyroid problems, and you get a B12 level [test] to exclude deficiencies in B12. The problem is that a diagnosis of exclusion is a grossly inaccurate approach. The diagnostic accuracy, at best, is 75 percent.”

Sharon Cohen, a clinician and director of the Toronto Memory Program, offered a similar estimate. “When we diagnose Alzheimer’s disease without a confirmatory test, we are wrong about 30 percent of the time,” Cohen told Being Patient.

Three factors have historically complicated Alzheimer’s diagnosis.

Overlapping symptoms and pathologies. Neurodegenerative diseases can look similar clinically, and they often coexist in the brain. “Pathologically pure Alzheimer’s without any other pathology is quite rare,” Sabbagh said. “It’s only like 33 to 40 percent. Most Alzheimer’s is mixed with something else — hippocampal sclerosis, vascular change, argyrophilic grain [disease], or Lewy body.”

Costly confirmatory testing. The tests that can more definitively identify Alzheimer’s pathology have historically been expensive and difficult to access. Amyloid PET scans, for example, can cost thousands of dollars and were not broadly covered by Medicare until a major policy change in October 2023.

Limited diagnostic expertise in primary care. “Fundamentally, it boils down to the fact that primary care physicians don’t feel comfortable making a diagnosis,” Sabbagh said. “They get 36 months of training, one month of neurology; if they’re lucky, they get one day in the cognitive clinic. Yet we lay everything on the back of a primary care physician who does not feel comfortable making these diagnoses.”

Jason Karlawish, a professor of medicine, medical ethics, health policy and neurology at the University of Pennsylvania and co-director of the Penn Memory Center, described the problem as both a workforce shortage and a reluctance to deliver the diagnosis.

“There is a reluctance on the part of some physicians to diagnose and name the disease,” he told Being Patient. “We just don’t have an adequate health care workforce to serve the needs of the many people who are experiencing cognitive changes.”

The consequences fall unevenly. One analysis of Medicare claims found Black Americans were twice as likely as white Americans to be underdiagnosed with dementia. Globally, Alzheimer’s Disease International estimates that up to three-quarters of people living with dementia have never received a diagnosis — equivalent to more than 40 million people.

Early signs of Alzheimer’s, and what mild cognitive impairment looks like

Before any test, there are the changes a person, or the people around them, begin to notice.

Three warning signs come up repeatedly in primary care: losing short-term memory, having trouble completing familiar or complex tasks, and becoming disoriented in a place that should be familiar. Neuropsychologist Emily Paolillo has also pointed to time disorientation, difficulty multitasking and navigation problems as possible signs of mild cognitive impairment, or MCI — a condition that can, but does not always, progress to dementia.

Sabbagh describes MCI as a category, not a cause. “MCI is cognitive impairment without functional impairment, still independent, but still having some cognitive issues,” he said. “Dementia is a category of definition of cognitive impairment with functional impairment. We want to capture people in the MCI phase.” The work, he added, is figuring out what’s driving it: “MCI only is a descriptive term, and the charge is to figure out what is the cause of MCI.”

Memory is not always the most noticeable early symptom, which can make cognitive decline harder to recognize. Michael Belleville, a patient advocate who was initially diagnosed with younger-onset Alzheimer’s at 52 before later receiving a Lewy body dementia diagnosis, noticed something else first.

“The things that showed up first weren’t just about memory,” Belleville told Being Patient. “Something that was happening more was my inability to multitask the way I used to be able to.” A communications technician at Verizon for nearly 20 years, he found himself asking colleagues he had personally trained how to do parts of his own job.

Mood and anxiety changes can also appear early. “Memory loss is certainly an early sign of Alzheimer’s, but frankly, mood and anxiety symptoms are an early sign, potentially, of dementia,” Brent P. Forester, an expert in geriatric psychiatry at Tufts University, told Being Patient. “It may be that it’s the underlying disease process coming out, and it’s manifesting with these psychiatric symptoms.” 

Barak Gaster, director of the University of Washington’s Cognition in Primary Care program, has emphasized that no single observation is enough on its own — and that the people around a patient can provide crucial information.

“The person experiencing cognitive decline might not realize what’s happening, but family members or friends will notice signs like repeatedly asking the same question or having trouble with familiar tasks,” he told Being Patient. “These observations, combined with cognitive test results, are essential for making an early diagnosis.”

What a cognitive screening test can — and can’t — tell you

The Montreal Cognitive Assessment, or MoCA, is one of the most widely used cognitive screening tools. The 30-point test takes about 10 minutes and assesses several areas of cognition, including short-term memory, executive function, attention, language, and visuospatial skills — including a clock-drawing task. 

In the study that originally validated the test, a score of 26 or higher was considered normal. Participants with mild cognitive impairment averaged 22.1, while those with Alzheimer’s disease averaged 16.2. 

Those numbers can provide useful clues, but a screening score is not a diagnosis. Performance can be influenced by factors unrelated to neurodegenerative disease, including education, hearing, and language proficiency. The standard MoCA is intended to be administered and interpreted in a clinical context; even self-administered cognitive screens are meant to flag whether further evaluation may be warranted, not determine whether someone has Alzheimer’s.

Doreen Monks, a neurology nurse for more than 40 years, spent decades giving these tests before she took one as a patient, describing their function precisely. “What mini-testing does, whichever one you use — it opens the door to investigation,” she said. “It doesn’t get you there to the diagnosis, it’s just the starting point.”

She argues for establishing a cognitive baseline well before symptoms raise concern, much like tracking blood pressure over time. “It takes maybe three minutes,” she said. “If you start doing baseline testing at 50, let’s say, the minute you pick up a glitch, you drop a point or two on their testing, whatever score you use, that’s where you start the evaluation.”

Ways doctors diagnose Alzheimer’s

Screening can reveal that something is wrong. Figuring out why requires a broader diagnostic workup — one that increasingly combines clinical evaluation with tests that can detect the biological hallmarks of Alzheimer’s.

Well established

Brain imaging. CT and MRI scans can reveal structural changes in the brain and help doctors look for other causes of cognitive symptoms, such as tumors, hydrocephalus or stroke. They cannot, on their own, confirm Alzheimer’s pathology. Amyloid PET scans can detect beta-amyloid plaques in the brain, while tau PET can detect the neurofibrillary tangles that are another hallmark of the disease.

Lumbar puncture. A lumbar puncture, or spinal tap, removes a small sample of the cerebrospinal fluid surrounding the brain and spinal cord. The fluid can then be tested for biomarkers associated with beta-amyloid plaques and tau tangles. 

It has a reputation problem that Sabbagh thinks is unearned. “We do lumbar punctures for meningitis, encephalitis, multiple sclerosis, and a dozen, two dozen other things, and there’s no reason not to do them for Alzheimer’s,” he said. “It’s a five-minute office procedure.” At the time of the interview, Sabbagh estimated that the procedure and analysis together cost about one-quarter as much as an amyloid PET scan. 

Emerging

Blood tests. Blood biomarkers are rapidly changing how Alzheimer’s is diagnosed. In May 2025, the FDA cleared the first blood test to aid in diagnosis, and by 2026 specialists were increasingly incorporating tests such as p-tau217 into routine workups for people with cognitive symptoms.

For Sabbagh, the blood test is currently the first step rather than the last. When a patient comes in with cognitive concerns, he now orders blood biomarkers alongside more traditional tests such as an MRI and neuropsychological testing. If the blood result is abnormal, he follows it with amyloid PET or spinal fluid testing for confirmation. “I’m not replacing the PET yet,” Sabbagh told Being Patient. “And I find that that stepped approach seems to be working pretty well.”

That approach reflects an important limitation: blood tests can improve diagnostic accuracy, but their performance varies across tests and settings. At the 2026 Alzheimer’s Association International Conference, researchers reported that adding a blood test improved diagnostic accuracy to 88 percent among primary care physicians and 93 percent among dementia specialists in a study of more than 1,300 people suspected of having Alzheimer’s. The test also changed the diagnosis in more than a quarter of cases. Being Patient reported that some FDA-cleared tests have performed less accurately in real-world studies than earlier validation data suggested.

For now, experts also caution against using these tests as general screening tools in people without symptoms. Current guidance does not recommend testing cognitively healthy people, Sabbagh said, because a positive biomarker result can not reliably predict when, or if, a person will develop cognitive decline.

In development

Skin tests. Researchers have explored whether Alzheimer’s-related cellular abnormalities can also be detected in skin. The DISCERN test uses a three-millimeter skin biopsy and analyzes three biomarkers. Its developers have reported accuracy above 95 percent in distinguishing Alzheimer’s from other conditions, though the test is not used in routine clinical practice. “I put the emphasis on accuracy, and it’s minimally invasive, very much like a blood draw,” Daniel Alkon, director of the Blanchette Rockefeller Neuroscience Institute, told Being Patient.

Retinal scans. Researchers are also studying whether changes in the retina could provide an early warning sign of Alzheimer’s. Because retinal tissue is part of the nervous system, it offers a noninvasive way to look for changes associated with disease. “It’s a rare opportunity to look at actual nervous system tissue for clues to the disease,” Peter Snyder, a professor of biomedical sciences at the University of Rhode Island, told Being Patient.

More recently, companies have begun pairing retinal imaging with artificial intelligence. RetiSpec, for example, is developing software that analyzes images from standard eye-exam cameras for signals associated with amyloid in the brain. The company says the test is designed to produce a real-time result and is being prepared for regulatory review.

Snyder has emphasized that such a tool would be used for screening rather than diagnosis: “A screening test is not the same as making a confirmatory diagnosis.”

“Don’t let doctors dismiss your complaints”

Meaningful changes in memory or thinking should be taken seriously and investigated.

“The patient should be asking about the new blood tests, the new scans, the new technologies; they should not be letting doctors dismiss their complaints,” Sabbagh  told Being Patient. “That makes me crazy,” he said. “If the patient complains about their memory, they should evaluate it or refer on. Tell the patients to keep going and don’t let the doctor talk them out of it.”

Monks makes the same case. “You have to become that person’s strongest advocate and demand further investigation,” she said. “If you had chest pain, you would expect that the physician would do a certain EKG. They’re not going to let it go; they’re going to do further testing. If there was a possibility of cancer, the same thing.” 

Her own primary care doctor did not think anything was wrong but referred her for further evaluation anyway. “She owned up to the fact that she wasn’t prepared to make any further diagnostic studies,” Monks said.

A few things can make that conversation more useful:

• Write down specific examples of what has changed, such as repeated questions, missed appointments, trouble with familiar tasks or getting disoriented in familiar places.
• Bring a full medication list, including over-the-counter drugs and supplements. Some medications can contribute to memory problems and should be reviewed as part of the workup.
• Bring someone who has noticed the changes. Clinicians often rely on a spouse, relative, or other “knowledgeable informant” to help establish whether cognition or day-to-day functioning has changed.
• Ask for a referral if necessary. “You’re looking for a geriatrician, neurologist or psychiatrist who states they evaluate and care for persons with cognitive complaints as part of their practice,” Karlawish said.

And if the diagnosis still does not make sense, a second opinion can be worthwhile. “Always, you should get a second opinion when you’re facing a deadly disease or a disease with a poor outcome,” said David Agus, a physician at the University of Southern California.

What happens after a diagnosis

An Alzheimer’s diagnosis is the beginning of a new set of decisions, not the end of the conversation. Common next steps include learning what living with dementia may involve, seeing a specialist, discussing treatment and lifestyle options, involving family in care planning, organizing legal and financial documents early, and considering participation in research.

Belleville’s advice focuses on something he felt was missing from his own care. After his diagnosis, he said he was given a prescription and told to return in six months, with no referral to a support group or guidance about what came next. For the next five or six months, he said, he largely withdrew.

“I like to tell folks, you get a prescription for a medication and I think one of the first prescriptions they should be giving people with a dementia diagnosis is for social engagement,” he said. “You can still live a meaningful, purposeful life.”

Why getting an Alzheimer’s diagnosis matters more now

Diagnosing Alzheimer’s has improved significantly in a short span of time. A diagnosis of exclusion is no longer the only option: spinal fluid analysis and amyloid PET can provide biological evidence of the disease, Medicare now covers amyloid PET scans more broadly, and FDA-cleared blood tests are available for people with cognitive symptoms. Tools that were speculative a decade ago — including retinal imaging, skin biopsies and AI-assisted analysis — are also moving through development.

What has not caught up is access. Specialist wait times can be long, primary care physicians often receive limited training in cognitive assessment, and the burden of pushing for further evaluation can still fall heavily on the person experiencing symptoms and their family.

Early diagnosis also matters more now because there is more that can follow from it: treatments that may slow progression in the earliest stages, evidence-based lifestyle interventions, clinical trials and more time to plan for the future.

The message from clinicians and patients alike is simple: meaningful changes in memory or thinking should be documented, evaluated, and not dismissed.

This article was adapted from the Being Patient guide to diagnosing Alzheimer’s and draws on Being Patient’s reporting and interviews with researchers and people living with dementia. It is intended for general information and is not a substitute for medical advice. If you or a loved one is experiencing changes in memory or thinking, consult a qualified healthcare professional.