Scientists have developed a new blood test to detect Alzheimer’s disease without the need for expensive brain imaging or a painful lumbar puncture, where a cerebrospinal fluid (CSF) sample is taken from the lower back. If the test is validated, it could enable faster diagnosis of the disease, which would lead to the initiation of therapies at an earlier stage.

Alzheimer's is a gradual condition that begins with modest memory loss and may proceed to loss of capacity to converse and respond to surroundings. However, diagnosis remains challenging, especially during the earlier stages of the disease.

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Current guidelines recommend detecting the following distinct markers: unusual accumulations of amyloid and tau proteins, as well as neurodegeneration, which is a slow and progressive decline of neuronal cell number in particular regions of the brain. The detection is done through brain imaging and CSF analysis, but a lumbar puncture can be painful and can lead to headaches or back pain, while brain imaging is costly and takes a long time to schedule.

“A lot of patients, even in the US, don’t have access to MRI and PET scanners. Accessibility is a major issue," Prof Thomas Karikari at the University of Pittsburgh, in Pennsylvania, who took part in the study, said.

Developing a reliable blood test would be a significant step forward.

“A blood test is cheaper, safer and easier to administer, and it can improve clinical confidence in diagnosing Alzheimer’s and selecting participants for clinical trial and disease monitoring,” Karikari said.

The current blood tests can detect abnormalities in amyloid and tau proteins accurately, but the detection of nerve cell damage markers that are specific to the brain has been more difficult. Karikari and his colleagues worked on developing an antibody-based blood test that would detect an Alzheimer's disease-specific form of tau protein called brain-derived tau.

In the research published in the Brain journal, the scientists tested 600 patients at various stages of the disease and found that levels of the protein correlated well with those of tau in the CSF, and were able to reliably differentiate Alzheimer’s from other neurodegenerative diseases. Protein levels also closely corresponded with the severity of amyloid plaques and tau tangles in brain tissue from individuals who had died of Alzheimer’s.

The next required step to validate the test is to have a broader range of patients, such as varied racial and ethnic backgrounds, and people suffering from different memory loss stages or other potential dementia symptoms.

Karikari hoped that monitoring brain-derived tau levels in the blood could improve the design of clinical trials for Alzheimer’s treatments.