New blood test reveals the extent of brain damage following a stroke—and makes the effects of treatment visible

A stroke is a medical emergency—but until now, imaging has only been able to detect further brain damage in the hours and days that follow to a limited and sporadic extent. While blood tests exist for many other organs to indicate acute injury, a comparable marker for the brain has been lacking until now. Researchers at LMU Medical Center and international partners are now showing that a new blood marker—brain-derived tau (BD-tau)—can track the extent of brain damage over time following an ischemic stroke.

BD-tau can also predict patients’ functional status months or even years later. It also highlights the differences resulting from successful revascularization and from a drug tested in a clinical trial. Beyond stroke, this blood marker could be applied to other neurological conditions. The study, led by first author Dr. Naomi Vlegels and first author Nicoló Luca Knuth, was published in the journal Science Translational Medicine.

In an ischemic stroke, a region of the brain no longer receives an adequate blood supply. Medical decisions for patients experiencing sudden paralysis or speech difficulties are currently based primarily on CT or MRI imaging. However, in the acute phase, these imaging studies usually provide only a snapshot of the current condition. Repeated examinations are logistically challenging, not always feasible, and imaging results often only partially reflect subsequent recovery.

While acute damage to the heart or kidneys can often be monitored with blood tests, the brain has lacked such a marker until now. “In clinical care, we therefore currently face the problem of not being able to continuously track the progression of brain damage, which limits our ability to make treatment decisions,” says PD Dr. Dr. Steffen Tiedt, a researcher at the Institute for Stroke and Dementia Research (ISD) and senior physician in the Stroke Unit of the Department of Neurology at LMU Medical Center in Munich.

As early as 2013, he therefore launched a study at LMU Medical Center with the goal of developing a reliable blood test capable of continuously monitoring brain damage and identifying the effects of treatment. His team has now identified brain-derived tau (BD-tau) as a blood marker that detects tau protein from the central nervous system—and does exactly that. In the study cohort established at LMU Medical Center, BD-tau was measured repeatedly from the time of admission through Day 7. Additionally, the results were validated in two independent multicenter cohorts. This included a biomarker-based analysis within a Phase 3 study. In total, data from over 1,200 stroke patients were included in the analyses.

A promising marker for the progression of brain damage

BD-tau levels in the blood reflected the extent of brain damage: even early levels, measured just a few hours after the onset of symptoms, were associated with the extent of the initial damage and predicted the subsequent size of the infarct. Furthermore, BD-tau reflected the dynamics over time: a steeper rise in the first 24 to 48 hours was associated with infarct growth. Elevated levels also occurred in the event of complications such as recurrent events. BD-tau was also a strong predictor of recovery and predicted functional status after 90 days and beyond at least as well as, or better than, other blood markers and even imaging-based infarct volumes.

Finally, BD-tau revealed treatment effects: following thrombectomy, the rise was smaller if the vessel could be fully reopened. In a randomised trial, the neuroprotective agent nerinetide resulted in a significantly smaller rise in BD-tau than placebo. “In the case of a stroke, we need not only an initial snapshot but also a way to track the progression of brain damage over time. BD-tau could become a kind of ‘troponin for the brain’ – an objective blood marker that makes the progression of damage and the effects of treatment measurable,” says Steffen Tiedt.

The researcher emphasises that further studies are needed, for example to define reference ranges and cut-off values and to be able to measure BD-tau more quickly in future (ideally as a point-of-care test). In the long term, such a blood test could help to monitor disease progression more effectively, detect complications earlier and evaluate new therapies more quickly in clinical trials. Furthermore, BD-tau could potentially also help to detect brain damage objectively and promptly in the blood in other neurological disorders.

Naomi Vlegels, Nicoló Luca Knuth et al. Brain-derived Tau for Monitoring Brain Injury in Acute Ischemic Stroke. Science Translational Medicine 2025