Checking for dementia involves a series of steps, not a single test. Doctors typically start with brief cognitive screening, then layer on blood work, brain imaging, and sometimes specialized biomarker tests to build a complete picture. The process can span several appointments over weeks or months, depending on how clear-cut the results are.
Cognitive Screening Tests
The first step is usually a short, structured test of your thinking and memory. Two tools dominate clinical practice: the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA). Both are scored out of 30 and take roughly 10 to 15 minutes to complete.
On the MoCA, a score of 26 to 30 is considered likely normal. A score of 20 to 25 raises the possibility of mild cognitive impairment or early dementia, and anything below 20 is suspicious for dementia. The MMSE uses a simpler cutoff: a score of 24 or below should raise concern. These tests check orientation (knowing the date, where you are), short-term recall, attention, language, and the ability to follow multi-step instructions. Some versions include drawing tasks, like copying a cube or drawing a clock face set to a specific time.
Neither test is a diagnosis on its own. They’re screening tools designed to flag problems that need further investigation. Someone with high education may score well despite real decline, while someone with limited schooling or a language barrier may score poorly without having dementia.
Ruling Out Depression
Depression in older adults can mimic dementia so closely that clinicians sometimes call it “pseudodementia.” Apathy, one of the hallmark symptoms of dementia, is often mistaken for depression, and older patients tend to report fewer emotional symptoms than younger ones. People with cognitive impairment may also underestimate their own emotional state because they can’t consistently reflect on how they’re feeling.
To tease the two apart, doctors use standardized depression scales. For people who don’t yet have a dementia diagnosis, a self-report tool called the Geriatric Depression Scale works well, with a sensitivity of about 88% and specificity of 82%. For people already showing signs of dementia, clinicians rely more on the Cornell Scale for Depression in Dementia, which draws on caregiver observations rather than self-report and reaches a sensitivity of 91% and specificity of 87% in that group. Sorting this out matters because depression is treatable, and memory problems caused by depression can improve significantly with the right care.
Neurological Exam
A neurological exam looks for physical signs that point toward specific brain conditions. The doctor is checking for evidence of stroke, Parkinson’s disease, brain tumors, fluid buildup in the brain, and other problems that can impair memory or thinking but aren’t dementia in the traditional sense.
During the exam, you’ll be asked to do things like follow an object with your eyes, squeeze the doctor’s hands, walk across the room, and respond to light touches on your skin. The doctor is specifically evaluating your reflexes, coordination, muscle tone and strength, eye movement, speech, and sensation. Abnormalities in any of these areas can redirect the diagnostic workup toward a different cause.
Blood Tests and Lab Work
Blood tests serve a critical purpose in the dementia workup: they identify reversible causes of memory loss. Several conditions can produce symptoms that look like dementia but are actually fixable.
The standard panel typically includes a complete blood count, a comprehensive metabolic panel (checking kidney and liver function), thyroid-stimulating hormone levels, and vitamin B12. Low B12 and an underactive thyroid are two of the most common treatable causes of cognitive decline in older adults. Doctors also test blood glucose levels, since poorly controlled diabetes can affect thinking. Depending on your history, the workup may include screening for infections known to affect the brain, such as HIV and syphilis, along with a toxicology screen to rule out drug or alcohol-related cognitive problems.
If all of these come back normal, it makes a neurodegenerative cause more likely, and the workup moves to imaging.
Brain Imaging
Brain scans let doctors see structural and functional changes inside the brain. The type of scan depends on what the doctor is looking for.
MRI and CT Scans
Both MRI and CT can detect masses, blood vessel problems, bleeding, and structural abnormalities. MRI is preferred for a more detailed look because it can pick up subtle tissue damage, patterns of brain shrinkage, and tiny areas of vascular disease that CT misses.
Different types of dementia leave distinct signatures on MRI. Alzheimer’s disease typically shows shrinkage in the hippocampus (the brain’s memory center) and in areas at the back and sides of the brain. Frontotemporal dementia shows shrinkage concentrated in the front and sides of the brain, with the back relatively preserved. Vascular dementia shows damage to the brain’s white matter, often with small strokes visible in deep brain structures. These patterns help doctors narrow down which type of dementia is most likely.
PET Scans
PET scans go a step further by measuring brain activity and detecting specific proteins. A glucose PET scan reveals which parts of the brain are using less energy than expected. Each dementia type produces a characteristic pattern of reduced activity. Alzheimer’s, for instance, shows decreased energy use first in areas near the center-back of the brain, then spreading outward to the sides and eventually the front.
Amyloid PET scans detect the sticky protein plaques associated with Alzheimer’s disease. A positive result means moderate to heavy plaque buildup; a negative result suggests little to no plaque. Tau PET scans detect a second problematic protein that forms tangles inside brain cells. Together, these molecular scans can confirm or rule out Alzheimer’s pathology with high confidence, though they’re not ordered for every patient. They’re most useful when the diagnosis is uncertain after other testing.
Spinal Fluid Analysis
A lumbar puncture (spinal tap) can measure proteins in the fluid surrounding the brain and spinal cord. Three core biomarkers make up what’s called the “Alzheimer’s disease profile.” The first is a protein fragment called amyloid-beta 42. When this protein gets trapped in brain plaques, less of it flows into the spinal fluid, so lower-than-normal levels actually suggest Alzheimer’s. The other two, total tau and phosphorylated tau, run in the opposite direction: higher levels indicate damage to brain cells.
This test is more invasive than a blood draw, so it’s typically reserved for cases where imaging and cognitive testing haven’t provided a clear answer.
Blood-Based Biomarker Tests
A newer and less invasive option is now available. In early 2025, the FDA cleared the first blood test for use in diagnosing Alzheimer’s disease. The test measures a ratio of two proteins in a standard blood draw and is approved for adults 55 and older who are already showing signs of cognitive impairment.
In clinical testing on 499 plasma samples, 91.7% of people who tested positive on the blood test were confirmed to have amyloid plaques by PET scan or spinal fluid analysis. Among those who tested negative, 97.3% were confirmed negative by those same methods. Less than 20% of patients received an indeterminate result. This test doesn’t replace imaging or cognitive assessment, but it gives doctors a faster, cheaper way to determine whether Alzheimer’s-related brain changes are present before ordering more expensive scans.
Genetic Testing
Genetic testing plays a limited role in most dementia evaluations. The gene most commonly associated with Alzheimer’s risk is APOE4, but carrying this gene variant doesn’t mean you’ll develop the disease, and not carrying it doesn’t mean you won’t. For this reason, most experts don’t routinely recommend genetic testing for the common late-onset form of Alzheimer’s, and most doctors don’t test for APOE genes in standard practice.
The exception is early-onset Alzheimer’s, which strikes before age 65 and is more likely to have a strong genetic component. In those cases, genetic testing may be useful for confirming a diagnosis and for informing family members about their own risk. Specific gene mutations tied to early-onset forms are rare but highly predictive when present.
How the Process Comes Together
No single test confirms or rules out dementia. Doctors piece together results from cognitive screening, physical exams, lab work, imaging, and sometimes biomarker tests to arrive at a diagnosis. The process typically unfolds over multiple visits. An initial appointment might include cognitive screening, a neurological exam, and blood work orders. Follow-up appointments address imaging results and, if needed, more specialized testing like PET scans or spinal fluid analysis.
For straightforward cases where cognitive screening, blood work, and an MRI all point in the same direction, a diagnosis may come within a few weeks. Complex cases, particularly when symptoms are mild or could stem from multiple causes, can take longer as doctors work through the differential. The goal isn’t just to determine whether dementia is present but to identify the specific type, since Alzheimer’s, vascular dementia, frontotemporal dementia, and Lewy body dementia each follow different trajectories and respond to different management strategies.