Overview and context

Alzheimer's disease is the most common form of dementia, marked by abnormal brain proteins such as beta-amyloid and phosphorylated tau. Traditional diagnostic methods—cognitive testing, MRI, PET scans, or lumbar punctures—can be slow, expensive, and not always readily accessible. In this Guardian Science Weekly episode, Ian Sample speaks with Jonathan Schott, a Professor of Neurology at the University College London Dementia Research Center, about a new blood test that detects phosphorylated tau 217 in the blood. Early results suggest higher diagnostic accuracy when used within the right clinical context, potentially moving from about 70% accuracy to as high as 95% in patients with cognitive impairment. The test is not a population screening tool and must be interpreted alongside clinical evaluation.

"Early diagnosis is at the heart of all of medicine" - Jonathan Schott

The blood test and the trial design

The trial will recruit 1,100 patients attending memory clinics across the NHS and involve around 20 memory centres. All participants will provide consent and have a blood test. Half will be told their results at three months, the other half at a year, to assess whether earlier results improve diagnostic certainty, influence patient experience, and affect the use and allocation of healthcare resources. The investigators aim to determine whether clinicians are comfortable using the test, whether it is acceptable to patients, and whether it is cost-effective enough to pass NICE review.

"the evidence suggests that in the right hands, the test can increase the accuracy of diagnosis from around 70 to 95 percent" - Jonathan Schott

Implications for diagnosis, treatment, and cost

Although a positive result on this blood test indicates a high likelihood of Alzheimer's changes in the brain, it does not by itself diagnose dementia. Clinicians will interpret the result in the full clinical context, and there will be intermediate results that do not clearly support a diagnosis. If validated, the test could become a gateway to disease-modifying therapies, potentially lowering overall diagnostic costs and enabling earlier treatment decisions. Two drugs, leanumab and danumab, show potential to slow disease progression, but NICE has deemed them not cost-effective so far. A cheaper, scalable blood test could shift the economics by refining who should receive expensive therapies and by shaping future pricing and negotiations with manufacturers.

"people can deal with uncertainty" - Jonathan Schott

Future directions and optimism

Beyond diagnostics, researchers are exploring ways to deliver therapies across the blood-brain barrier. Innovations such as transferrin-based shuttles may allow anti-amyloid treatments to reach the brain more efficiently, potentially requiring smaller doses with fewer side effects. Early trials using transferrin receptor–based delivery show promising clearance of brain amyloid with favorable safety profiles. The field is buoyed by renewed investment and a sense of turning point after years of limited options, with the blood test serving as a galvanizing tool for research and clinical trials.

"there are exciting results with transferrin-based shuttles that could deliver drugs directly to the brain" - Jonathan Schott

In sum, while there are still significant hurdles, the episode frames a future in which affordable, scalable diagnostics and targeted therapies could transform the management of dementia and improve lives for patients and families alike.

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