Tests for diagnosing dementia

There's no single test for dementia. A diagnosis is based on a combination of assessments and tests. These may be done by a GP or a specialist at a memory clinic or hospital.

Taking a history

This is usually done by a GP. If you're referred to a specialist, a more detailed history will be taken.

It helps if someone who knows you well is also with you, as they can help describe any changes or problems they've noticed.

The doctor will:

• ask how and when your symptoms started and whether they're affecting your daily life
• check whether any existing conditions, such as heart disease, diabetes, depression or stroke, are being properly managed
• review any medicines you're taking, including prescribed medicines, those bought over the counter from pharmacies, and any alternative products, such as vitamin supplements

Mental ability tests to diagnose dementia

People with symptoms of dementia are given tests to check their mental abilities, such as memory or thinking.

These tests are known as cognitive assessments, and may be done initially by a GP.

There are several different tests. A common one used by GPs is the General Practitioner Assessment of Cognition (GPCOG).

Although these tests cannot diagnose dementia, they may show there are memory difficulties that need further investigation.

Most tests involve a series of pen-and-paper tests and questions, each of which carries a score.

These tests assess a number of different mental abilities, including:

• short- and long-term memory
• concentration and attention span
• language and communication skills
• awareness of time and place (orientation)

It's important to remember that test scores may be influenced by a person's level of education.

For example, someone who cannot read or write very well may have a lower score, but they may not have dementia.

Similarly, someone with a higher level of education may achieve a higher score, but still have dementia.

Blood tests to check for other conditions

Your GP will arrange for blood tests to help exclude other causes of symptoms that can be confused with dementia.

In most cases, these blood tests will check:

• liver function
• kidney function
• thyroid function
• HbA1c (to check for diabetes)
• vitamin B12 and folate levels

If your doctor thinks you may have an infection, they may also ask you to do a urine test or other investigations.

Read more about blood tests.

Dementia brain scans

Brain scans are often used for diagnosing dementia once the simpler tests have ruled out other problems.

Like memory tests, on their own brain scans cannot diagnose dementia, but are used as part of the wider assessment. 

Not everyone will need a brain scan, particularly if the tests and assessments show that dementia is a likely diagnosis.

These scans may also be used to check for evidence of other possible problems that could explain a person's symptoms, such as a stroke or a brain tumour.

An MRI scan is recommended to:

• help confirm a diagnosis of dementia and the type of disease causing the dementia
• provide detailed information about the blood vessel damage that happens in vascular dementia
• show shrinkage in specific areas of the brain – for example, the frontal and temporal lobes are mainly affected by shrinkage in frontotemporal dementia, while usually just the temporal lobes are affected in the early stages of Alzheimer's disease

A CT scan can be used to check for signs of stroke or a brain tumour. But it cannot provide detailed information about the structure of the brain.

Even if a brain scan does not show any obvious changes, this does not mean someone does not have dementia.

Other scans and procedures to diagnose dementia

Other types of scan, such as a SPECT scan or a PET scan, may be recommended if the result of your MRI or CT scan is uncertain.

However, most people will not need these types of scans.

Both SPECT and PET scans look at how the brain functions, and can pick up abnormalities with the blood flow in the brain.

If a specialist is worried that epilepsy may be causing the dementia symptoms, an EEG may be taken to record the brain's electrical signals (brain activity), but this is rare.

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