Assessing for dementia is a multi-step process that combines cognitive screening, a detailed personal history, functional evaluation, lab work, and brain imaging. No single test confirms or rules out dementia on its own. Instead, clinicians layer several types of evidence to determine whether cognitive decline is present, how severe it is, and what’s causing it.
Why Assessment Takes Multiple Steps
Memory loss and confusion can stem from dozens of causes, many of them treatable. Vitamin B12 deficiency, an underactive thyroid, depression, medication side effects, and even urinary tract infections in older adults can all mimic dementia. A thorough assessment isn’t just about identifying cognitive problems. It’s about separating irreversible brain disease from reversible conditions that look similar.
Gathering History From the Person and Someone Close to Them
The assessment typically starts with two conversations: one with the person being evaluated and one with a family member, partner, or close friend. The informant interview is critical because people in early stages of dementia often underestimate or don’t notice their own decline.
One widely used informant tool is the AD8, an eight-item questionnaire. A family member is asked whether they’ve noticed changes in things like judgment, interest in hobbies, or the ability to remember appointments. Each “yes, a change” answer scores one point. A score of 2 or higher suggests possible very mild dementia, while a cutoff of 4 provides a more balanced reading when distinguishing people who do and don’t have dementia.
Clinicians also ask about the timeline. When did changes first appear? Did they come on gradually or suddenly? A slow, steady decline over months or years points toward a neurodegenerative disease. A sudden change after surgery, a fall, or a new medication suggests something else entirely.
Cognitive Screening Tests
Two screening tools dominate clinical practice: the Mini-Mental State Exam (MMSE) and the Montreal Cognitive Assessment (MoCA). Both are scored out of 30 and take about 10 to 15 minutes.
The MMSE tests orientation (knowing the date and location), memory recall, attention, language, and simple drawing tasks. A score of 24 or above is generally considered normal. The MoCA covers those areas plus executive function, abstract reasoning, and delayed recall, making it more sensitive to early and subtle cognitive changes. A score of 26 or above is considered normal on the MoCA, with an extra point added for people with fewer than 12 years of formal education.
Head-to-head comparisons show the MoCA is the stronger screening tool. In studies comparing the two, the MoCA had better overall diagnostic accuracy, particularly for catching early-stage decline that the MMSE misses. For people in a prodromal stage, where symptoms are emerging but not yet obvious, the MoCA correctly identified 83% of cases compared to the MMSE’s weaker performance at the same threshold. The tradeoff is that the MoCA is harder, so it can sometimes flag people who are cognitively healthy but less educated or less test-savvy.
Detecting cognitive impairment is a required element of Medicare’s Annual Wellness Visit. This doesn’t always mean a formal screening tool. Clinicians can also flag concerns through direct observation or reports from family members about changes in memory, judgment, or medication management.
Evaluating Daily Functioning
Cognitive test scores alone don’t determine whether someone has dementia. The key distinction between mild cognitive impairment and dementia is functional impact: has the cognitive decline started interfering with the person’s ability to manage daily life?
Clinicians look at two levels of function. Basic activities of daily living (ADLs) include bathing, dressing, eating, using the toilet, and moving around. These tend to remain intact until moderate or advanced stages. Instrumental activities of daily living (IADLs) are more complex: managing finances, preparing meals, shopping for groceries, keeping up with medications, doing laundry, using a phone, and arranging transportation. IADL problems show up earlier and are often the first concrete sign that something beyond normal aging is happening.
If your parent has always managed the household bills but is now missing payments, or has cooked for decades but suddenly can’t follow a recipe, those IADL changes carry real diagnostic weight. Tools like the Lawton Instrumental Activities of Daily Living Scale systematically assess these abilities across eight domains.
Blood Tests to Rule Out Reversible Causes
Standard lab work is a non-negotiable part of any dementia workup. The American Academy of Neurology recommends screening for vitamin B12 deficiency and hypothyroidism, both of which can cause cognitive symptoms that improve with treatment. A basic metabolic panel checks for kidney or liver dysfunction, electrolyte imbalances, and blood sugar problems that can cloud thinking. Depression screening is also part of the standard evaluation, since depression in older adults frequently presents as memory and concentration problems rather than sadness.
These tests won’t diagnose Alzheimer’s or other neurodegenerative conditions, but they can catch the treatable mimics that account for a meaningful percentage of cognitive complaints in older adults.
Brain Imaging
Most dementia assessments include a structural brain scan, typically an MRI. The primary purpose is twofold: rule out other conditions (tumors, strokes, fluid buildup in the brain) and look for patterns of brain shrinkage that point toward specific types of dementia.
In Alzheimer’s disease, the hippocampus, the brain’s memory hub, is hit earliest and hardest. A meta-analysis of over 1,800 people found that hippocampal volume was already reduced by about 20% even at a mild stage of Alzheimer’s. Shrinkage in the temporal and parietal lobes follows, though these changes are more variable. White matter damage, visible on specialized MRI sequences, affects the connections between the hippocampus and other brain regions involved in memory retrieval and spatial awareness.
More advanced imaging like PET scans can detect amyloid plaques and abnormal tau protein deposits in the brain. These aren’t part of a routine first assessment but become relevant when the diagnosis is uncertain or when a person is being evaluated for newer targeted treatments.
Blood-Based Biomarkers
A newer development is blood tests that measure specific proteins linked to Alzheimer’s disease. The most promising is phosphorylated tau 217, a protein fragment that rises in the blood years before symptoms appear. In research studies, p-tau217 measurements were approximately 90% accurate at identifying people with Alzheimer’s-related brain changes, performing as well as PET imaging and spinal fluid testing. Levels correlated with disease development up to 20 years before symptoms emerged.
The 2024 revised diagnostic criteria from the Alzheimer’s Association now recognize that an abnormal result on certain core biomarkers, including accurate plasma tests, is sufficient to establish an Alzheimer’s diagnosis across the disease spectrum. This represents a shift toward defining Alzheimer’s as a biological process rather than waiting for a clinical syndrome to fully develop. That said, blood-based biomarkers are still being validated in large, diverse populations and aren’t yet standard in every clinical setting.
Distinguishing Between Types of Dementia
Not all dementia is Alzheimer’s. The assessment process also aims to determine which type of dementia a person has, because this affects prognosis, symptoms to watch for, and treatment options.
Lewy body dementia, the second most common type, has a distinctive signature. Diagnosis generally requires ongoing cognitive decline plus at least two of the following: vivid visual hallucinations, Parkinson’s-like movement symptoms (stiffness, slow movement, tremor), or noticeable fluctuations in alertness and attention throughout the day. People with Lewy body dementia often act out their dreams during sleep, physically moving or calling out, sometimes years before other symptoms appear. They may also experience drops in blood pressure upon standing and difficulty regulating body temperature. In Alzheimer’s, hallucinations typically don’t appear until about four years into the disease. In Lewy body dementia, they show up early.
Vascular dementia follows a different pattern, often appearing in a stepwise fashion after strokes or in the context of chronic small vessel disease visible on brain imaging. Frontotemporal dementia tends to strike younger, often between ages 45 and 65, and initially affects personality, behavior, or language more than memory.
What the Full Assessment Looks Like
Putting it all together, a comprehensive dementia evaluation typically unfolds over one to three visits and includes:
- Clinical interview with the patient and an informant who knows them well
- Cognitive screening using a validated tool like the MoCA or MMSE, sometimes followed by more detailed neuropsychological testing
- Functional assessment evaluating both basic self-care and more complex daily tasks
- Lab work to rule out thyroid problems, vitamin deficiencies, infections, and metabolic issues
- Brain imaging to identify structural changes and exclude other conditions
- Mood evaluation to screen for depression or anxiety that could be contributing to symptoms
In some cases, particularly when results are ambiguous or the person is young, the workup expands to include formal neuropsychological testing (a battery of tests lasting several hours that maps strengths and weaknesses across specific cognitive domains), biomarker blood tests, or PET imaging. The goal is always the same: establish whether dementia is present, identify the cause, and catch anything that might be treatable.