Blood tests that look for signs of Alzheimer’s disease are moving closer to routine clinical use, but a central challenge remains: a promising biomarker can also rise in people with other neurological or muscular conditions. Researchers at University Medicine Halle report a method intended to make those tests more specific by adding an antibody-based step that distinguishes forms of the tau protein.
The study, published in Nature Communications, involved 315 participants. Its authors say the approach improved the ability to distinguish Alzheimer’s disease from other conditions that can otherwise complicate interpretation of a blood test.
Why p-tau217 needs context
Many commercial blood tests focus on phosphorylated tau 217, generally called p-tau217. Levels of that biomarker can increase early in Alzheimer’s disease, before severe cognitive symptoms such as short-term memory problems are apparent. That timing makes it an attractive candidate for identifying people who may need further assessment.
But a raised p-tau217 result is not, by itself, a definitive diagnosis. Neurologists at University Medicine Halle reported in 2025 that the marker could also be elevated in people with amyotrophic lateral sclerosis, or ALS. The newer work starts from that limitation: diseases affecting the brain, nerves or muscles may contribute to higher tau-related signals in blood.
The distinction matters because an imprecise result can direct patients toward the wrong clinical pathway. It also matters as antibody treatments for Alzheimer’s become available. According to the researchers, those therapies must be started in the disease’s earlier stages, increasing the value of an accurate way to identify appropriate patients.
Separating tau sources
Tau is not a single uniform molecule. The research team describes smaller tau forms, known as brain-derived tau, that occur mainly in the brain. A larger form, called big tau, is found in peripheral nerves, muscles and possibly other tissues.
Conventional blood tests cannot reliably separate those forms, according to Markus Otto, director of the Department of Neurology at University Medicine Halle and a senior author of the work. That limitation can make a signal originating outside the brain look more like evidence for Alzheimer’s disease than it should.
The team’s proposed solution is an added antibody step that helps identify the relevant tau isoform signatures. Rather than treating every p-tau217-related signal as equivalent, the method is designed to account for the form of tau present and, by extension, its likely source.
A potential guardrail against false positives
The study’s reported result is an improvement in diagnostic discrimination, not a replacement for clinical judgment. Blood-based biomarkers can make testing more accessible and less burdensome than some alternatives, but their usefulness depends on how well clinicians can separate an Alzheimer’s-related signal from similar signals associated with other disorders.
That is particularly important for people with ALS and potentially for patients with diseases involving nerves or muscles. If big tau or other non-brain sources influence a conventional measurement, a positive result could lead to unnecessary concern or follow-up. A test that identifies the source-related tau form could provide a useful guardrail.
The findings also illustrate a broader point about biomarker development. A marker may be sensitive enough to reveal biological change early, yet still lack the specificity needed for a stand-alone answer. Improving a test can mean not only detecting more signal, but determining which signal belongs to the disease being investigated.
What the study does and does not establish
The Halle researchers tested their method in 315 participants and report better accuracy in differentiating Alzheimer’s disease from other conditions. The work was published in a peer-reviewed journal, but the supplied findings do not establish that the antibody step has been incorporated into commercial tests or that it is ready to change clinical practice immediately.
Those questions will depend on further validation across settings and patient populations, as well as on how the method performs alongside established diagnostic assessments. Alzheimer’s diagnosis is based on more than a single laboratory value, and the source material does not claim otherwise.
Still, the study addresses a practical weakness in the growing field of blood-based Alzheimer’s testing. By distinguishing tau signatures that are more closely associated with the brain from those associated with peripheral tissues, the researchers aim to make a widely watched biomarker more reliable when it matters most: early in the decision process.
Why earlier certainty matters
For patients and clinicians, a better test is not simply a technical advance. Earlier and more accurate identification may help determine who should receive additional evaluations and who may be eligible for treatments that work best when begun early. It may also reduce the risk that a non-Alzheimer’s condition is mistaken for evidence of the disease.
The new work does not resolve every uncertainty around Alzheimer’s blood testing. It does, however, offer a specific strategy for handling one of the field’s most important sources of ambiguity: tau does not come from one place, and tests that can recognize that difference may produce more dependable results.
This article is based on reporting by Medical Xpress. Read the original article.
Originally published on medicalxpress.com
