Scientists have developed a blood test to diagnose Alzheimer’s disease without the need for expensive brain imaging or a painful lumbar puncture, where a sample of cerebrospinal fluid (CSF) is drawn from the lower back. If validated, the test could enable faster diagnosis of the disease, meaning therapies could be initiated earlier.

Alzheimer’s is the most common form of dementia, but diagnosis remains challenging – particularly during the earlier stages of the disease.

Current guidelines recommend detection of three distinct markers: abnormal accumulations of amyloid and tau proteins, as well as neurodegeneration – the slow and progressive loss of neuronal cells in specified regions of the brain. This can be done through a combination of brain imaging and CSF analysis. However, a lumbar puncture can be painful and people may experience headaches or back pain after the procedure, while brain imaging is expensive and takes a long time to schedule.

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

The development of a reliable blood test would be an important step forwards. “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.

Although current blood tests can accurately detect abnormalities in amyloid and tau proteins, detecting markers of nerve cell damage that are specific to the brain has been harder. Karikari and his colleagues around the world focused on developing an antibody-based blood test that would detect a particular form of tau protein called brain-derived tau, which is specific to Alzheimer’s disease.

They tested it in 600 patients at various stages of Alzheimer’s and found that levels of the protein correlated well with levels of tau in the CSF, and could reliably distinguish Alzheimer’s from other neurodegenerative diseases. Protein levels also closely corresponded with the severity of amyloid plaques and tau tangles in brain tissue from people who had died with Alzheimer’s. The research was published in the journal Brain.

The next step will be to validate the test in a broader range of patients, including those from varied racial and ethnic backgrounds, and those suffering from different stages of memory loss or other potential dementia symptoms.

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