A simple test that checks the levels of a certain protein in the blood could “reliably rule out” Alzheimer’s in those being investigated for the disease, according to its developers.

There are hopes it will offer reassurance to patients with cognitive decline and help them avoid unnecessary further testing, researchers said.

The Elecsys Amyloid Plasma Panel, developed by Roche, checks levels of phosphorylated Tau (pTau) 181, which increases in people with Alzheimer’s disease.

For many people, getting a clear and timely diagnosis remains challenging. This test could help patients to receive the right care at the earliest opportunity

The trial included 492 patients from across the US, Europe and Australia aged between 55 and 80.

All had memory concerns that classified them as having subjective cognitive decline or mild cognitive impairment or had mild dementia and were being assessed for Alzheimer’s.

Researchers found the test achieved a high negative predictive value of 96.2%, which means that if a patient tests negative, there is a 96.2% chance they do not have Alzheimer’s-related brain changes.

Of the 492 patients, 23.4% had amyloid plaques in the brain, as confirmed by PET scans.

The test demonstrated 91% sensitivity, which means it was able to correctly identify 91% of people who have amyloid plaques.

It also had a 69.8% specificity, which means it was able to correctly show a negative result for about 70 out of 100 people who don’t have plaques.

Matt Sause, chief executive of Roche Diagnostics, said: “The data from this large-scale study in cognitively impaired individuals suggests that a fast and simple blood test could reliably rule out amyloid pathology, offering much-needed reassurance to patients and their families.

“Alzheimer’s disease is one of the most challenging health issues of our time, and its impact on society is growing as the world’s population ages.

“For many people, getting a clear and timely diagnosis remains challenging. This test could help patients to receive the right care at the earliest opportunity.”

It is thought about 982,000 people in the UK are living with dementia, with some waiting up to a year for diagnosis.

The test can accurately rule out Alzheimer's as a possible cause of cognitive decline symptoms with a more than 90 per cent specificity, offering reassurance with a simple blood test and avoiding unnecessary further testing

The process usually involves a combination of assessments and tests, either carried out by a GP, at hospital or at specialist memory clinics.

These are followed by blood tests to rule out other conditions with similar symptoms, brain scans and a lumbar puncture to test the spinal fluid.

Professor Dag Aarsland of the Institute of Psychiatry, Psychology and Neuroscience at King’s College London, was involved with the study, which has been presented at the 17th Clinical Trials in Alzheimer’s Disease congress (CTAD) in Madrid.

He said: “Currently, diagnosis is largely based on clinical manifestation and biomarker confirmation requires invasive tests that draw spinal fluid.

“The test can accurately rule out Alzheimer’s as a possible cause of cognitive decline symptoms with a more than 90% specificity, offering reassurance with a simple blood test and avoiding unnecessary further testing.”

According to Prof Aarsland, Roche plans to secure a CE mark – a label that indicates a product meets the European Union’s (EU) safety, health, and environmental protection standards – for the test in late 2025, which he says “could open up availability across Europe”.

He added: “There is huge interest among doctors working with people with dementia to get access to these new tests.

“Widespread adoption will depend on proving these tests are reliable and cost-effective.”

Reacting to the findings, Dr Sheona Scales, director of research at Alzheimer’s Research UK, said: “The results of this trial appear to show that the Elecsys Amyloid Plasma Panel can accurately rule out amyloid pathology, which is one of the signs that Alzheimer’s disease is present.

“However, the blood test is still under development and other assessments confirming the absence of amyloid pathology, such as lumbar puncture and PET scans are still needed.

“And while the test rules out amyloid pathology, people had cognitive decline, so other forms of dementia or other underlying health conditions would still need to be investigated.”

Dr Richard Oakley, associate director of research and innovation at Alzheimer’s Society, added: “Blood testing is likely to become a crucial stage in getting a dementia diagnosis, it’s therefore really encouraging that this new blood test from Roche could help rule out Alzheimer’s disease for people who are experiencing memory issues and could be another tool to understand the cause of their symptoms.

“This test is very accurate at correctly identifying when people with memory complaints don’t have amyloid in their brain, which we know builds up in the brain of those with Alzheimer’s disease and can be measured in the blood.

“While the company say it will avoid unnecessary further tests, patients would still need to have further investigations to find out what is affecting their memory, even if Alzheimer’s disease can be ruled out with this blood test.”