Alzheimer’s: a new ‘two-in-one’ blood test to detect the disease is on the way

At the end of August, the US Food and Drug Administration gave the green light to a new blood test for the diagnosis of Alzheimer’s disease, the Elecsys pTau217, developed by Roche in collaboration with Eli Lilly. It is not the first blood test to be approved for this disease, but it is the first capable, from a single blood sample, of confirming or ruling out the presence of the amyloid pathology typical of Alzheimer’s in adults over the age of 55 who show signs or symptoms of cognitive decline.

The test measures the plasma concentration of pTau217, a phosphorylated form of the tau protein which tends to increase at an early stage in the course of Alzheimer’s disease, whilst it remains essentially normal in other neurodegenerative conditions. Although it is a marker of the tau protein, pTau217 measured in the blood correlates closely with the presence of amyloid in the brain, the other protein whose accumulation, in the form of plaques, is considered one of the biological ‘signatures’ of Alzheimer’s. According to Laura Nisenbaum, interim scientific director of the Alzheimer’s Drug Discovery Foundation, the strength of this new test lies in the fact that it has well-validated and standardised normal reference ranges applicable in both general and specialist medical practice.

Over the past two years, the field of blood tests for Alzheimer’s has expanded rapidly. In May 2025, the FDA authorised Fujirebio’s Lumipulse G pTau217/β-amyloid 1-42 Plasma Ratio, which calculates the ratio between two biomarkers; also in 2025, Roche’s Elecsys pTau181 received approval, although it is intended solely to rule out amyloid pathology in general practice settings. Finally, in the same week as the approval of the Elecsys pTau217, the FDA also gave the go-ahead to C2N Diagnostics’ Precivity AD2. “The unique feature of the new Roche-Lilly test,” emphasises Dung Trinh, Medical Director of the Healthy Brain Clinic in Irvine (USA), “is that it is a single-biomarker test capable of confirming or ruling out the disease, using the same normal cut-off value, in any clinical setting.”

The new test is carried out using a standard blood sample, and is only performed on patients aged 55 and over who exhibit cognitive impairment. The results may be positive for amyloid pathology, negative or intermediate, and must always be interpreted by a doctor, alongside other clinical information, to determine the next steps in the diagnostic process. In short, it is not a test that one can request for oneself, nor is it recommended for mass screening of healthy, asymptomatic people.

The enthusiasm for the ease of carrying out this new test also stems from a huge problem. Around 75 per cent of dementia cases worldwide remain undiagnosed, mainly because traditional confirmatory tests (amyloid PET scans and lumbar punctures) are expensive, invasive and only available at specialist centres. Furthermore, diagnosis usually takes place 3.5 years after the first symptoms appear. “Just a year ago, there wasn’t even a single FDA-approved test for Alzheimer’s,” recalls Nisenbaum. “Today we have as many as four.” In short, blood tests for diagnosing Alzheimer’s are no longer a promise for the future, but are becoming part of routine clinical practice. And this changes everything: from the design of future studies, to the development of new drugs, to the advice that can be given to patients and their families.