A new, more accurate blood test for Alzheimer’s disease has been circulating in the news. But what is the new test? How does it work? And what are the implications for the future diagnosis and treatment of Alzheimer’s?

4 minute read

What is Alzheimer’s disease?

Alzheimer’s disease is the most common cause of dementia, a condition that affects over 50 million people worldwide. It causes damage to the brain and is a degenerative disease, which means it gets worse over time.

Alzheimer’s disease causes damage to the brain in several ways, one of which is the formation of beta-amyloid plaques that build up between neurons (nerve cells in the brain) and stop them from working properly. One type of beta-amyloid protein, beta-amyloid 42 (A-beta 42) is thought to be particularly harmful. 

Further damage to the brain occurs when another protein called tau clumps together to form tangles inside neurons. This blocks the neuron’s transport system and damages communication between them.   

The first symptoms of Alzheimer’s disease are usually memory problems and forgetfulness, but as the condition progresses, it can cause further problems, including: 

• Confusion and disorientation

• Difficulty making plans or decisions

• Speech problems and difficulty understanding language (dysphasia)

• Personality changes, such as becoming more aggressive or suspicious

• Hallucinations (seeing things that are not there)

• Delusions (believing things that are not true)

• Loss of independence

• Depression and anxiety

How is Alzheimer’s disease diagnosed? 

Diagnosing Alzheimer’s disease isn’t a straightforward process, and until now, there hasn’t been a simple test to diagnose the condition. 

Traditionally, Alzheimer’s disease has been diagnosed in several ways: 

• Assessing your symptoms and performing tests to check your memory, mental ability, speech, and communication skills.

• A blood or urine test to check for other medical conditions that could be causing your symptoms.

• Scans such as a CT (computerised tomography), or MRI (magnetic resonance imaging). These cannot diagnose Alzheimer’s disease but can confirm or rule out diseases with similar symptoms such as a brain tumour, or stroke. They can also show whether the brain has lost mass (shrunk) which can be a sign of Alzheimer’s disease.

• An amyloid-PET (positron emission tomography) scan measures the buildup of abnormal amyloid protein in the brain, a key sign of Alzheimer’s disease

• A lumbar puncture (where a needle is inserted into the spine and fluid removed) to check the levels of amyloid proteins in the spinal fluid

Alzheimer’s disease progresses slowly, and many people put their symptoms down to “getting old”. By the time most people are diagnosed with Alzheimer’s, their symptoms are usually quite severe, and they have probably had the disease for some time, which can make it harder to treat. 

What treatments are available for Alzheimer’s disease?

There is currently no cure for Alzheimer’s disease, but there are treatments available to improve symptoms. These include: 

• Medications such as acetylcholinesterase (AChE) inhibitors, memantine, anti-psychotics and anti-depressants

• Cognitive stimulation therapy (CST) — group therapy aimed at improving memory and problem-solving skills 

• Cognitive rehabilitation — learning everyday tasks and skills by using parts of the brain that are working to help the parts of the brain that are not 

• Reminiscence/ life story work — talking about events in the past and compiling photos, items and notes from your life can help improve Alzheimer’s patients overall mood and wellbeing

How do the new blood tests work to diagnose Alzheimer’s disease?

Beta-amyloid 42/40 ratio

This test measures the ratio between 2 types of amyloid beta proteins in the blood, A-beta 40, and A-beta 42. These are known as biomarkers, which give us information about our health and measure the likelihood of developing certain diseases. Beta-amyloid proteins are known to build up in the brains of people with Alzheimer’s disease, causing damage to the brain and triggering symptoms of the disease. 

The test also measures apolipoprotein E (ApoE) variants in the blood to see whether you carry the APOE4 mutation, a gene that increases your risk of developing Alzheimer’s disease. 

The combination of the A-beta 42/40 ratio and whether you carry the APOE4 gene are used to determine your amyloid probability score (how likely you are to develop Alzheimer’s disease). Your amyloid probability score is given as a range and is expressed as low, intermediate, or high. 

p-tau217

A new 2-step blood test has recently been developed to measure another biomarker in the blood called p-tau217. The result is combined with the patient’s age and the presence of the APOE4 mutation to diagnose Alzheimer’s in people with mild symptoms of the disease.  

The second step involves testing cerebrospinal fluid (CSF) to determine the A-beta 42/40 ratio and is only used when the results of the blood test are unclear.

What are the benefits of the new blood test? 

The new blood test for Alzheimer’s may have several benefits, including: 

Convenience and cost

A blood test to diagnose Alzheimer’s is quick, easy, and relatively painless. It can be done in a clinic or doctor’s surgery, reducing the need for lengthy assessments by specialists, expensive diagnostic scans, and unpleasant procedures such as a lumbar puncture.

Lower cost and ease of use should make the test more widely available in the future, leading to more people receiving an early diagnosis and treatment. 

Early detection

Amyloid proteins can start to build up in the brain up to two decades before the symptoms of Alzheimer’s disease appear. The new test is able to measure these proteins and detect Alzheimer’s disease much earlier than previous diagnostic methods.

Detecting Alzheimer’s in the early stages, or before you start showing symptoms of the disease, can allow you to make the necessary lifestyle changes to help slow the progression of the disease. Some treatments for Alzheimer’s disease, such as medication, may also be more effective when started in the early stages. 

Accuracy 

A study published in the medical journal Neurology compared the A-beta 42/40 ratio tests of 465 participants with the results of amyloid PET scans and cerebrospinal fluid (CSF) tests. The study concluded that the A-beta 42/40 ratio blood test is up to 93% accurate at diagnosing early Alzheimer’s disease. 

Who should have the new blood test for Alzheimer’s? 

A blood test for Alzheimer’s may be beneficial if you are experiencing early symptoms of Alzheimer’s disease, such as memory loss, or if you have a family history of the disease. 

Summary 

An accurate blood test to diagnose Alzheimer’s disease is a major breakthrough in the early diagnosis and treatment of this common, but often devastating, condition. Early diagnosis allows patients to make necessary lifestyle changes and start treatment that could potentially slow the progression of the disease.