Checking for dementia starts with recognizing patterns that go beyond normal forgetfulness, then moves through screening tools you can use at home and, if needed, a medical evaluation that includes cognitive testing, blood work, and brain imaging. No single test confirms dementia on its own. The process works by layering evidence from multiple sources to build a clear picture.
Normal Aging vs. Early Warning Signs
Before anything else, it helps to understand what’s worth worrying about and what isn’t. Forgetting where you put your keys once in a while is normal at any age. Regularly misplacing things and being unable to retrace your steps is not. The National Institute on Aging draws a useful line between the two:
- Normal: Making a bad decision once in a while. Concerning: Making poor judgments and decisions frequently.
- Normal: Missing a monthly payment. Concerning: Ongoing problems managing monthly bills.
- Normal: Forgetting which day it is and remembering later. Concerning: Losing track of the date or time of year entirely.
- Normal: Sometimes forgetting which word to use. Concerning: Trouble holding a conversation.
- Normal: Losing things from time to time. Concerning: Misplacing things often and being unable to find them.
Other red flags include asking the same questions repeatedly, getting lost in familiar places, having trouble following recipes or directions, growing confused about people and places, and neglecting self-care like eating, bathing, or personal safety. Any of these patterns showing up consistently, not as a one-off, warrants a closer look.
Screening Tools You Can Use at Home
Two well-validated screening tools let you start gathering information before a doctor’s visit. Neither one diagnoses dementia, but both flag cognitive changes worth discussing with a physician.
The SAGE Test (Self-Administered)
The Self-Administered Gerocognitive Exam, developed at Ohio State University, is a pen-and-paper test designed to detect early cognitive impairment. You print it out, answer the questions in ink without help from anyone else, and avoid looking at a clock or calendar while taking it. It takes about 10 to 15 minutes with no time limit. Four interchangeable versions exist, and you only need to complete one.
In validation studies, SAGE detected cognitive impairment with 79 percent sensitivity and a false positive rate of just 5 percent. Its questions are intentionally harder than those on other common screening tools, which helps it catch very mild impairments that easier tests miss. Once you finish, bring your answer sheet to your doctor for scoring and discussion.
The AD8 (For Family Members)
If you’re concerned about someone else, the AD8 is an eight-question screening interview designed for a family member or close friend to complete. It asks whether you’ve noticed changes in the person’s:
- Judgment and decision-making
- Interest in hobbies or activities
- Tendency to repeat questions, stories, or statements
- Ability to learn new tools or devices
- Knowledge of the correct month or year
- Handling of complicated financial matters like taxes or bills
- Ability to remember appointments
- Day-to-day thinking and memory
The AD8 is available through the Alzheimer’s Association. A “yes” to two or more items suggests cognitive changes that should be evaluated professionally. What makes it valuable is that people in early stages of decline often don’t recognize changes in themselves, but the people around them do.
What Happens During a Medical Evaluation
A doctor’s assessment for dementia is more thorough than any home screening. It typically involves three components: a neurological exam, blood tests, and cognitive testing.
During the neurological exam, a provider checks multiple aspects of nervous system function. This includes testing strength, coordination, reflexes, balance, and sensation in different parts of the body. You may be asked to close your eyes and touch your nose, move your arms and legs in specific ways, or demonstrate fine motor skills like writing your name. Cranial nerve testing covers eye movements, facial movements, vision, hearing, and sense of smell. For the cognitive portion, expect questions about the date, time, and where you are, along with tasks like repeating a short sequence of words.
Blood work screens for conditions that can mimic dementia but are treatable. Thyroid hormone levels, vitamin B12, and markers of infection are standard. This step matters because hypothyroidism, B12 deficiency, depression, and even certain nutritional gaps caused by excessive alcohol use (particularly thiamine deficiency) can all produce memory problems and confusion that look like dementia but improve or resolve with the right treatment. Subdural hematomas and brain tumors can also cause cognitive symptoms, which is why imaging is part of the workup.
Brain Imaging and What It Reveals
MRI and PET scans let doctors see structural and functional changes in the brain that point toward specific types of dementia. In Alzheimer’s disease, MRI typically shows shrinkage in the hippocampus (the brain’s main memory center), along with thinning in areas responsible for spatial awareness and language. PET scans reveal reduced brain activity that starts in regions involved in memory retrieval and self-awareness, then spreads to areas handling language and spatial processing, and eventually reaches the frontal lobes.
Frontotemporal dementia looks different. MRI shows shrinkage concentrated in the frontal and temporal lobes, the areas that govern personality, behavior, and language, while the back of the brain remains relatively intact. PET scans confirm reduced activity in those same frontal regions. These distinct patterns help doctors tell one type of dementia from another, which matters because the progression, symptoms, and management differ.
Blood Tests for Alzheimer’s Biomarkers
A newer development in dementia diagnosis is the ability to detect Alzheimer’s disease through a blood draw. A test measuring a protein called p-tau217, which rises when Alzheimer’s-related brain changes are underway, has been validated in outpatient memory clinics. In a study of 509 patients at Mayo Clinic, the blood test confirmed Alzheimer’s with 95 percent sensitivity and 82 percent specificity. It correctly identified 233 out of 246 patients whose cognitive problems were caused by Alzheimer’s.
This is a significant shift from the traditional diagnostic process, which often relied on spinal fluid samples or expensive PET scans to confirm Alzheimer’s biology. The 2024 criteria from the National Institute on Aging and Alzheimer’s Association now define Alzheimer’s by its biology rather than its symptoms alone, and include plasma p-tau217 as a core diagnostic option alongside spinal fluid tests. The practical impact is that confirmation of Alzheimer’s is becoming faster and less invasive than it used to be, though availability still varies by location and clinical setting.
How a Formal Diagnosis Is Made
A formal dementia diagnosis under current psychiatric criteria requires evidence of decline in one or more cognitive domains, confirmed by standardized testing, combined with a meaningful loss of everyday functioning. The severity is graded based on what the person can still do independently. Mild dementia means difficulty with complex tasks like managing money or keeping up with housework. Moderate dementia involves trouble with basic activities like dressing and feeding. Severe dementia means full dependence on others.
This functional dimension is key. Someone who scores poorly on a cognitive test but manages daily life without difficulty would not meet the threshold for a dementia diagnosis. The combination of measurable cognitive decline and real-world functional loss is what separates dementia from milder forms of cognitive impairment.
Conditions That Mimic Dementia
Not everything that looks like dementia is dementia, and this is one of the most important reasons to get a full medical evaluation rather than relying on a screening tool alone. Depression can cause concentration problems, memory lapses, and withdrawal from activities that closely resemble early dementia. Hypothyroidism slows thinking and causes brain fog. Vitamin B12 deficiency produces confusion and memory problems that can be reversed with supplementation. Chronic heavy drinking leads to thiamine deficiency, which causes a specific pattern of memory loss and disorientation known as Wernicke encephalopathy, and early treatment with thiamine can prevent permanent damage.
Structural problems in the brain, including bleeding between the skull and brain surface or tumors, can also produce cognitive symptoms that improve once the underlying problem is addressed. The standard blood panel and brain imaging ordered during a dementia workup are specifically designed to catch these reversible causes before anyone is given a diagnosis they may not actually have.