There is no single test that can diagnose dementia. Diagnosis requires a combination of cognitive screening, blood work, brain imaging, and clinical evaluation, pieced together over one or more visits with a doctor. The process is designed to both identify cognitive decline and rule out treatable conditions that can mimic dementia, like thyroid problems or vitamin deficiencies.
Cognitive Screening Tests
The quickest tools doctors use are short, in-office cognitive tests that take 10 to 30 minutes. The two most common are the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA). Both are scored out of 30. On the MMSE, a score of 24 or above is generally considered normal. The MoCA uses a cutoff of 26, with an extra point added for people with fewer than 12 years of formal education.
These tests check orientation (do you know the date and where you are?), memory recall, attention, language, and the ability to copy a simple drawing. The MoCA covers a broader range of thinking skills, including abstract reasoning and executive function, which makes it somewhat better at catching earlier or subtler changes. Neither test gives a definitive diagnosis on its own. A low score signals the need for deeper investigation, while a normal score doesn’t completely rule out early problems.
There’s also a shorter option called the Mini-Cog, which takes about three minutes and combines a word-recall task with a clock-drawing test. It’s often used as a quick first screen in primary care.
Self-Administered Screening at Home
If you’re concerned about yourself or a family member, the SAGE test (Self-Administered Gerocognitive Examination) is a validated pen-and-paper test you can take at home and bring to your doctor. Developed at Ohio State University, it takes about 15 minutes and tests memory, problem-solving, and language. In clinical studies, SAGE detected dementia with 100% sensitivity using a cutoff score below 18 out of 22, and identified mild cognitive impairment with about 91% sensitivity at a cutoff below 20. It’s free to download, though it’s not a replacement for a professional evaluation. Think of it as a useful starting point for a conversation with your doctor.
Blood Tests That Rule Out Other Causes
One of the first things a doctor will do is order blood work to check for conditions that cause memory problems but are fully treatable. The American Academy of Neurology specifically recommends screening for vitamin B12 deficiency and hypothyroidism, both of which can produce symptoms that look like dementia but resolve with treatment. Depending on the situation, doctors may also check folate levels, vitamin B1, calcium (to assess parathyroid function), liver and kidney function, and blood sugar. Infections like syphilis and HIV can also cause cognitive decline, so those may be tested as well.
These blood tests matter because an estimated subset of dementia cases involve potentially reversible causes, including medication side effects, depression, nutritional deficiencies, and metabolic conditions. Ruling these out is a critical early step.
The New Blood Test for Alzheimer’s
In May 2025, the FDA cleared the first blood test specifically designed to help diagnose Alzheimer’s disease. Made by Fujirebio, the Lumipulse test measures the ratio of two proteins in blood plasma: p-tau217 and beta-amyloid 1-42. These proteins reflect the amyloid plaques that build up in the brains of people with Alzheimer’s. Previously, detecting these plaques required either a spinal tap or an expensive PET scan, so a simple blood draw is a major shift in accessibility.
The test is cleared for adults 55 and older who are already showing signs of cognitive decline. It is not a screening test for people without symptoms, and it’s not meant to be used alone. Doctors are expected to combine the results with other clinical evaluations before making a diagnosis or treatment decision. Still, it represents a practical leap forward, particularly for patients who don’t have easy access to specialized imaging centers.
Brain Imaging
CT and MRI scans show the physical structure of the brain. They can reveal shrinkage in regions associated with Alzheimer’s (particularly the hippocampus, involved in memory), evidence of strokes that point to vascular dementia, tumors, or a buildup of fluid called normal pressure hydrocephalus. These scans don’t diagnose dementia directly, but they help narrow down the cause and rule out structural problems.
PET scans go further by showing how the brain is functioning. A common type uses a glucose tracer to measure brain activity. Areas with reduced glucose use suggest damaged or dying tissue. More specialized PET scans can detect amyloid plaques and tau tangles, the hallmark proteins of Alzheimer’s disease. Amyloid PET scans have high sensitivity for detecting plaque buildup in living patients. Other PET tracers can identify problems with dopamine-producing brain cells, which helps distinguish Lewy body dementia from Alzheimer’s. These advanced scans are typically reserved for cases where the diagnosis is unclear after initial testing.
Spinal Fluid Analysis
A lumbar puncture (spinal tap) allows doctors to measure Alzheimer’s-related proteins directly in cerebrospinal fluid. In people with Alzheimer’s, levels of amyloid-beta 42 drop by roughly 30 to 50% compared to healthy people of the same age, because the protein gets trapped in brain plaques instead of flowing freely. At the same time, levels of tau protein rise, reflecting nerve cell damage. This combination of low amyloid and high tau is a strong biological signal of Alzheimer’s disease. Spinal fluid testing has been used primarily in research and specialized memory clinics, though the new blood test may reduce how often it’s needed going forward.
Neuropsychological Testing
When screening tests flag a problem but the picture isn’t clear, a neuropsychologist can perform a detailed evaluation lasting several hours. This battery of tests measures memory, language, attention, problem-solving, visuospatial skills (like judging distances or copying shapes), and processing speed. Memory testing consistently shows the strongest ability to distinguish people who will develop dementia from those who won’t.
These evaluations also help identify which type of dementia someone has. Alzheimer’s tends to affect memory first, while frontotemporal dementia often shows up as personality changes or language difficulties. Vascular dementia may cause more trouble with attention and processing speed than with memory. The pattern of strengths and weaknesses across cognitive domains gives doctors important diagnostic clues.
The Neurological Exam
A standard neurological exam checks reflexes, coordination, muscle strength, eye movements, balance, and gait. The doctor will watch you walk, test whether you can walk heel-to-toe in a straight line, and check for involuntary movements. They may look for “primitive” reflexes like a grasp reflex (your hand involuntarily clasping when your palm is stroked) or a snout reflex (your lips puckering when tapped), which can reappear in dementia as the brain loses higher-level control.
This exam also helps identify other neurological conditions. Reduced arm swing, hand tremor, or difficulty maintaining balance when gently pulled backward suggest a parkinsonian disorder. One-sided weakness, visual field loss, or abnormally brisk reflexes on one side point toward vascular dementia caused by strokes. These physical findings guide the doctor toward the right diagnosis and the right next tests.
Genetic Testing
Genetic testing is not part of a routine dementia workup. The most well-known genetic risk factor, the APOE-e4 gene variant, increases the likelihood of developing Alzheimer’s but does not guarantee it. Many people carry the variant and never develop dementia, while others develop Alzheimer’s without it. Because of this, APOE testing is used mainly in research settings to identify study participants.
The exception is early-onset Alzheimer’s, which strikes before age 65 and sometimes runs strongly in families. In these cases, a doctor may test for rare mutations in three specific genes (APP, PSEN1, and PSEN2) that directly cause the disease. These mutations are deterministic, meaning carriers will almost certainly develop Alzheimer’s, but they account for a very small fraction of all cases.
How the Pieces Fit Together
No single test confirms or rules out dementia. Instead, diagnosis works by layering evidence. A typical path starts with a medical history and cognitive screening in a primary care office, followed by blood work to rule out reversible causes, brain imaging to look for structural changes, and possibly referral to a specialist for neuropsychological testing or biomarker analysis. The newer blood test for amyloid may streamline part of this process, but it supplements rather than replaces the broader evaluation. Each piece of evidence narrows the possibilities until the doctor can identify not just whether dementia is present, but what type it is and how far it has progressed.