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Researchers at University Medicine Halle have developed a new method that could improve the reliability of blood tests for Alzheimer’s disease. Current commercial tests often rely on the protein biomarker p-tau217, whose levels can rise in the early stages of the disease. However, the biomarker levels can also be elevated in other conditions, potentially leading to false-positive results. In a study involving 315 participants, the research team demonstrated improved accuracy in distinguishing Alzheimer’s disease from other conditions. Their findings have been published in Nature Communications.
Early and accurate diagnosis is crucial for patients who may benefit from recently approved antibody treatments for Alzheimer’s disease, as these therapies must be initiated in the early stages of the disease. Blood tests are one promising diagnostic tool, offering considerable potential for identifying these patients. Many of these tests measure a phosphorylated form of the tau protein known as p-tau217. Blood levels of this biomarker can rise long before severe cognitive symptoms, such as short-term memory impairments, appear.
However, in 2025, neurologists at University Medicine Halle demonstrated that elevated levels of this biomarker alone are not a reliable indicator of Alzheimer’s disease. They also found elevated levels in people with amyotrophic lateral sclerosis (ALS), a disease affecting the motor nervous system. Diseases affecting the brain, the nerves or the muscles may therefore contribute to increased biomarker levels in the blood.
The tau protein exists in several forms. Smaller forms, known as "brain-derived tau", occur mainly in the brain, while a larger form, known as "big tau", is found in peripheral nerves, muscles and possibly other tissues. "Conventional blood tests cannot reliably distinguish between these different forms of tau," explains Professor Markus Otto, Director of the Department of Neurology at University Medicine Halle and senior author of the study. "Consequently, elevated p-tau217 levels may incorrectly indicate Alzheimer’s disease when they are actually associated with a muscle or nerve disorder."
To address this issue, a research team led by Professor Otto developed a method to improve the diagnostic accuracy of the established p-tau217 blood test. The new approach has two steps. First, a specific antibody is used to isolate brain-derived tau from the blood sample before it is measured.
The researchers then compared the conventional test with the new method using blood samples from 315 participants: 101 people with Alzheimer’s disease, 139 people with ALS and 75 control participants. The samples were collected at neurological centers in Halle and Mannheim, Germany and Milan, Italy.
The conventional test indicated elevated p-tau217 levels in both the Alzheimer’s and ALS groups. When the additional antibody step was included, however, the picture changed: "p-tau levels were elevated in people with Alzheimer’s disease, but not in those with ALS or in the control group," explains Dr. Samir Abu Rumeileh, consultant neurologist at the Department of Neurology at University Medicine Halle and first author of the study. "In our cohort, the method therefore clearly distinguished between the two diseases."
Comparative analyses of brain, spinal cord and muscle tissue conducted using mass spectrometry helped explain these results. Brain-derived p-tau217 was virtually absent from muscle tissue. This indicates that brain-derived p-tau217 measured in the blood originates from the brain and reflects Alzheimer’s-related changes there. The researchers therefore propose using the new method alongside existing blood tests in clinical practice. "A conventional p-tau217 test could provide a first indication of Alzheimer’s disease. If the result does not fit the clinical picture, or if a muscle or nerve disorder might be influencing the measurement, the two-step method can help clarify the result. This would reduce false-positive results and help identify more reliably the patients who are eligible for the new Alzheimer’s therapies," says Dr. Abu Rumeileh.
These findings could also have implications for ALS research. In the future, blood tests that target the large tau forms could help researchers evaluate muscle and nerve damage in people with ALS and track disease progression without requiring invasive procedures.
Additional research is necessary before the new method can be adopted for widespread clinical use. The measurement process must first be standardized and validated in larger, independent patient cohorts. Nevertheless, the research team believes that the method has the potential to become part of routine diagnostics.
Background
Researchers around the world are working to develop simple, reliable methods for detecting Alzheimer’s disease at an early stage. Tau protein plays a key role in these efforts. Under normal conditions, tau protein helps stabilize the internal structures that support nerve cells and their long extensions. In people with Alzheimer’s disease, however, tau becomes excessively phosphorylated, detaches from these supporting structures and forms aggregates inside nerve cells. These deposits disrupt communication between cells and eventually contribute to nerve cell death. These changes begin years before typical symptoms such as memory problems appear.
Funding was provided by the Clinician Scientist and Roux programs of the Faculty of Medicine at Martin Luther University Halle-Wittenberg, the German Federal Ministry of Research, Technology, and Space (BMFTR), the Italian Ministry of Health and the Italian Ministry of University and Research.
University Medicine Halle
Department of Neurology
Professor Markus Otto, Director
Dr. Samir Abu Rumeileh, Senior Physician
neurologie@uk-halle.de
Abu-Rumeileh, S., Großkopf, H., […], Otto, M. et al. Tau isoform mapping across tissues and biofluids reveals a signature distinguishing Alzheimer’s disease from amyotrophic lateral sclerosis. Nat Commun 17, 10745 (2026). https://doi.org/10.1038/s41467-026-78390-3
https://www.umh.de/en/news/alzheimer-diagnose-mittels-bluttest-biomarker-weniger... Press release regarding the previous study
http://umh.de/neurologie Department of Neurology at University Medicine Halle
Prof. Markus Otto (back), Dr. Samir Abu Rumeileh (right), and mass spectrometry expert Dr. Hennig Gr ...
Copyright: University Medicine Halle
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