Dementia tests: How dementia is diagnosed

The tests used to diagnose dementia

A diagnosis usually brings together four things. Each one looks at a different part of the picture, and a specialist reads them together.

Your history

A doctor or nurse asks about the changes you or your family have noticed, when they started and how they affect daily life. They also ask about other health conditions and any medicines you take. It helps to have someone with you who knows you well, as they may have noticed things you have not.

Memory and thinking tests

These are short pen-and-paper tests and questions, which can also be done by video. They check memory, concentration, language and orientation, such as knowing the date and where you are.

GPs often use a brief test, such as the General Practitioner Assessment of Cognition (GPCOG). Specialists use longer tests that look at more areas of thinking in more detail.

A score on its own does not diagnose dementia, and a normal score does not rule it out. Scores can also be affected by other things, such as how many years of education someone has had, so a specialist reads them alongside the other results.

Blood tests

Blood tests look for other conditions that can cause problems with memory and thinking, some of which can be treated. They usually check how well your liver, kidneys and thyroid are working, your average blood sugar level (HbA1c) and your vitamin B12 and folate levels.

A blood test on its own does not diagnose dementia.

Brain scans

A brain scan shows the structure of the brain. It can show shrinkage in particular areas or damage from small strokes, and it can rule out other causes, such as a brain tumour. The pattern of changes can help show which type of dementia someone has.

The most common scans are magnetic resonance imaging (MRI), which uses a magnetic field, and computed tomography (CT), which uses X-rays. Both are painless. You lie still while the scanner takes pictures.

If the cause is still unclear, a specialist may suggest another type of scan that shows how the brain is working, such as a SPECT or PET scan (single photon emission computed tomography or positron emission tomography). They may also suggest a lumbar puncture, which tests the fluid around the brain and spinal cord for proteins linked to Alzheimer's disease.

Can you test for dementia online?

Online questionnaires and apps cannot diagnose dementia. Some may help you decide whether it is worth speaking to a doctor, but a diagnosis needs a full assessment.

If you are worried about your memory, or about someone close to you, speak to your GP or a specialist service. Memory problems have many possible causes, and some of them can be treated.

Blood tests for Alzheimer's disease

Researchers are studying blood tests that measure a protein linked to Alzheimer's disease, called p-tau217. In the UK, the ADAPT trial began recruiting in August 2025. It plans to recruit 1,100 people at 20 specialist NHS centres and is testing whether giving these results early in an assessment helps doctors make a diagnosis.

These blood tests are not yet part of routine NHS diagnosis. We can add a p-tau217 blood test to our assessment for £500.00, but we do not offer it as a test on its own.

Genetic tests are different

A genetic test looks at inherited risk. It does not diagnose dementia. Some genes change the chance of developing dementia without deciding it. Carrying the e4 version of the APOE gene, for example, is linked with a higher risk of Alzheimer's disease, but many people with e4 never develop it.

If you are thinking about a genetic test, a consultation before the test helps you understand what a result can and cannot tell you.

How to get tested for dementia

Through the NHS

Start by speaking to your GP. They can look for other causes, carry out a short memory test and arrange blood tests. If dementia is possible, they can refer you to a memory clinic, sometimes called a memory assessment service, for a specialist assessment.

Privately

You can book a private assessment directly, without a GP referral. At The Dementia Service, the assessment includes:

• A cognitive examination with a mental health nurse, by video at home or at our London Waterloo clinic
• A blood test at your chosen address
• A brain scan at one of over 200 scan centres across the UK
• A 24-hour heart rhythm monitor, sent to your home
• An appointment with a consultant old age psychiatrist, who reviews every result and confirms your diagnosis

Your first appointment is available the same week, and from booking to diagnosis typically takes 20 working days. The full assessment costs £2,999.00, payable in two equal instalments. With a face-to-face nurse appointment at our London Waterloo clinic it costs £3,499.00, or £3,999.00 with face-to-face nurse and consultant appointments. With your consent, we send your report to your GP.

Preparing for your tests

• Write down the changes you or your family have noticed, and roughly when they started.
• Make a list of any medicines you take.
• If you can, bring someone who knows you well.
• Bring your glasses or hearing aids if you use them, so the tests reflect how you usually do.

Questions about dementia tests

Is there a single test for dementia?

No. A diagnosis comes from several tests looked at together by a specialist, usually a memory and thinking test, blood tests and a brain scan, along with your history.

Can a GP test for dementia?

A GP can carry out first checks, including a short memory test and blood tests, to look for other causes. If dementia is possible, they can refer you to a memory clinic for a specialist assessment.

Does a normal memory test score rule out dementia?

No. Guidance from the National Institute for Health and Care Excellence (NICE) says dementia should not be ruled out only because someone has a normal score on a memory test. A specialist looks at all of the results together.

Can a blood test detect dementia?

Not on its own. Blood tests look for other causes of memory problems. Blood tests for Alzheimer's disease are being studied in the UK but are not yet part of routine NHS diagnosis.

How long do the results take?

It depends on the service. In our assessment, from booking to diagnosis typically takes 20 working days.

Sources

1. NHS: Tests for diagnosing dementiaLast reviewed 17th July 2023
2. National Institute for Health and Care Excellence: Dementia: assessment, management and support for people living with dementia and their carers (NG97)Last reviewed 26th September 2023
3. Alzheimer's Society: UK trial launches to transform Alzheimer's diagnosis with simple blood test9th September 2025