How could blood biomarkers transform dementia diagnosis?

With an estimated third of people living with dementia currently undiagnosed, there is a clear need to improve the speed and accuracy of dementia diagnosis. Alzheimer's Society is hoping to achieve this through the Blood Biomarker Challenge.

What is the Blood Biomarker Challenge? 

Alzheimer’s Society, Alzheimer’s Research UK, together with the National Institute for Health and Care Research (NIHR), have jointly launched the game-changing Blood Biomarker Challenge which could revolutionise the way dementia is diagnosed.    

The project, which is possible thanks to a £5m award raised by players of People’s Postcode Lottery, will gather the information needed to introduce a blood test for dementia into UK healthcare systems.  

Why is the Blood Biomarker Challenge needed?  

We don’t want a world where the NHS has dementia drugs available but people are unable to access them because they don’t have the diagnosis they need. Yet that’s the future we’re hurtling towards.  

Current diagnosis of dementia in the UK relies on cognitive tests which assess the severity of a person’s symptoms.

Specialised brain scans or lumbar punctures are needed to measure the presence of key proteins which build up in the brains of people living with Alzheimer’s disease.

They will also be needed to confirm eligibility for new amyloid antibody treatments should they become available to patients in the UK.

This is because doctors would need to make sure a person has the target of the drug, amyloid, present in their brain before being able to start treatment. 

Making dementia diagnosis more accessible

However, as well as Cerebrospinal Fluid tests being invasive, these diagnostic tests are expensive, and not available to many memory assessment services.

This means that in some cases people may be told that they have dementia, but the clinician doesn’t have access to the tests to find out which disease of the brain is causing their dementia.

Blood-based biomarkers are poised to be a critical tool for dementia diagnosis in the future, by helping speed up the diagnosis process.

Obtaining vital evidence of biomarker accuracy

Blood tests for Alzheimer’s disease exist and have been extensively tested in research studies to show that they are accurate in diagnosing Alzheimer’s disease. They are also used in distinguishing it from other diseases that cause dementia.   

However, we are lacking the evidence to implement these blood tests into the NHS as they have not been tested in diverse patient groups in the UK. This evidence is crucial to their roll out and so more research is needed before they are ready to be used in a clinical setting in the UK. 

What is a blood biomarker?

Biomarkers are different medical signs that we can test which can be used to suggest whether a person has a disease or is at risk of developing it.

For example, taking a person’s temperature can be used as a biomarker for infection, or measuring the amount of iron in the blood can be a biomarker for whether or not a person is deficient in iron.    

Biomarkers can be detected in bodily fluids such as the blood, providing valuable information about what is happening in other parts of the body.  

How can Alzheimer’s disease be diagnosed using blood testing? 

Researchers are now developing biomarker tests that can detect two proteins called amyloid or tau proteins in the blood. These proteins both build up in the brain in Alzheimer’s disease, and when detected in blood could be used to indicate that they are also present in the brain.  

As amyloid and tau protein build up in the brain, our body tries to clear away these proteins. As a result, they can end up in spinal fluid, the special liquid which surrounds the brain and spinal cord and protects them.

Spinal fluid is connected to our blood stream by the brain-blood barrier. While researchers do not fully understand how these proteins reach the blood, theories include: 

• The brain-blood barrier becomes leaky in Alzheimer’s disease and allows amyloid/tau to escape into the blood. 
• Amyloid/tau protein can be produced in other parts of the body and naturally finds its way into the blood. 

When will we see biomarkers for dementia diagnosis being used in clinical practise?

For blood tests to be used in clinical practice, they must reach the same level of sensitivity and specificity as spinal fluid tests that are currently used in the NHS.

The Blood Biomarker Challenge will begin to build the evidence needed to show that blood testing for the diseases that cause dementia is accurate for patients with suspected dementia living in the UK. It is important to also ensure that this testing fits within the NHS Healthcare system.  

In early 2024, we’ll find out which researchers will take the project forward.