What are blood tests and blood biomarkers for diagnosing dementia?

A blood-based biomarker is an indicator about a person’s health that can be measured by testing their blood. Find out more about blood tests and blood-based biomarkers for dementia diagnosis. 

What is a blood-based biomarker? 

A biomarker is an indicator which could suggest whether a person has a disease, or a risk of developing it. A biomarker can be a specific process, a molecule, or protein that we can measure in the body, which informs us about a person's health.  

For example, measuring iron levels in the blood could tell us if a person has anaemia or detecting genetic mutations could tell us if a person is likely to develop certain diseases.  

A blood-based biomarker is an indicator about a person’s health that can be measured by testing their blood.  

How can a blood test detect Alzheimer’s disease? 

In Alzheimer's disease, there is an abnormal build-up of proteins in the brain, which are thought to be toxic to brain cells and lead to the disease symptoms. These proteins are called amyloid and tau proteins.  

As amyloid and tau proteins build up in the brain, the body tries to clear them away. As a result, these proteins can cross into a spinal fluid surrounding the brain and spinal cord. The spinal fluid is connected to our blood, which means that these proteins can cross into the blood and could be tested for by a blood test. As these proteins are specific to Alzheimer’s disease, a blood test like this could help doctors distinguish between Alzheimer’s disease and other types of dementia, which would mean a more accurate diagnosis.  

There are different types of dementia, including Alzheimer's disease, vascular dementia, Lewy Body Dementia, and frontotemporal dementia.  

Each type of dementia has a different cause and would require a tailored blood test to detect the early changes that would allow for an early diagnosis. However, these are not available yet.  

This is why, Alzheimer’s Society, in collaboration with Alzheimer's Research UK and the National Institute for Health and Care Research (NIHR), and supported by Gates Ventures, will pilot a project called the Blood Biomarker Challenge, where researchers will investigate the use of blood tests in the NHS for Alzheimer’s disease as well as other dementia types. This five-year project, supported by a £5 million award from People’s Postcode Lottery, hopes to revolutionise how dementia is diagnosed in the UK. 

No, these blood tests are not yet available on the NHS or privately.  

In January 2024, news broke about a research study from Sweden, which looked at detecting p-tau217 (a variant of the tau protein) in the blood. The study found that this blood test could be just as accurate in predicting if someone has Alzheimer’s disease in the brain as other more invasive tests. The study is a hugely welcome step in the right direction. 

However, we still need to know how these tests work in the real world, away from research labs. We need to know if the tests are reliable at detecting Alzheimer’s disease in diverse populations, with other health conditions and in NHS clinics and labs across the country. We also need to develop blood tests to detect other types of dementia, which will ensure that patients can get tailored support and treatments once they are available.  

That is why the Blood Biomarker Challenge will help us understand how effective blood tests are in diagnosing different types of dementia, in real-life settings. The project will gather the information needed to introduce blood tests for dementia diagnosis into UK healthcare systems.   


Dementia is the UK's biggest killer. There are 900,000 people living with dementia in the UK. However, a third of people living with dementia do not have a diagnosis.  

Currently, dementia is diagnosed using memory and thinking tests as well as scans that look at the structure of the brain. These do not show the proteins that are building up in the brain. For this, more advanced techniques are needed. Two ways we can detect these proteins are through specialised brain scans (called Positron Emission Tomography or PET scans) or by measuring them in spinal fluid. However, both methods require a specialised workforce and equipment, and are invasive. They are also not widely available. 

Blood testing is important, as it is an inexpensive way that we can detect the diseases that cause dementia, early and accurately. This is crucial as it allows people to access care and support they need, and plan for their future. New treatments are being developed, such as lecanemab and donanemab, which appear to slow disease progression in people with early Alzheimer’s disease. Therefore, for people to be eligible to receive them, they need an accurate and early diagnosis.  

Knowing which type of dementia people have is important, as for people living with other types of dementia, where there are no treatments available yet, getting an accurate and early diagnosis will allow them to participate in research and clinical trials that can lead to dementia breakthroughs and new treatments being developed. An early and accurate diagnosis will also help patients to access the care and support they need, understand their diagnosis more, and plan for the future. 

Research into blood-based biomarkers will also allow us to understand the diseases better, including their causes and processes that are happening in the body. Therefore, it is possible that new knowledge will be discovered that will lead researchers to develop new ways of treating dementia.  

Unfortunately, we cannot directly signpost people to specific research regarding the Blood Biomarker Challenge. The research teams that will be carrying out the projects will handle trial recruitment themselves once the project starts.  

For more information about the Blood Biomarker Challenge and how to take part, please visit Dementias Platform UK

Currently, there is no cure for dementia. However, new treatment options are being developed, new breakthroughs emerging, and there are 141 drugs in clinical trials right now. 

There are some symptomatic treatments available. These medicines help manage the symptoms of dementia but do not slow it down. For more information about these, head to our information page

For Alzheimer’s disease, potential disease modifying drugs are undergoing review in the UK by our regulatory bodies. These drugs are designed to clear the root cause of the disease, which is an abnormal build-up of the amyloid proteins in the brain. The drugs are called lecanemab and donanemab and, if approved, would be suitable for people with early stages of Alzheimer’s disease. 

If you are worried about your symptoms, or symptoms of a loved one, please visit our dementia symptom checklist, which can help you describe symptoms to a GP or health professional and give you current information on how to get a diagnosis. 

If you would like to speak to someone, please contact our Dementia Support Line on 0333 150 3456. Our dementia advisers will listen and give you support and advice and connect you to the help you need. Phone support is available seven days a week. 

You can also access peer support through our Dementia Support Forum.  

How to get a dementia diagnosis

Read our support information to find out what to expect when getting a diagnosis.

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