Researchers at Washington University School of Medicine in St. Louis have identified a blood biomarker that could help detect advanced chronic traumatic encephalopathy (CTE), a degenerative brain disease associated with repeated head injuries. The discovery could represent an important step toward identifying the condition in living people, something that has remained a major challenge in neurological research because CTE can currently be confirmed only through examination of brain tissue after death.
The study, published in the medical journal JAMA on November 13, 2026, identified a protein fragment called eMTBR-tau243 as a potential indicator of CTE-related changes in the brain. Researchers found elevated levels of the marker in blood samples from people with autopsy-confirmed CTE. However, the findings are preliminary: the test could not reliably identify early-stage disease, and larger studies are needed before it can be used to diagnose patients clinically.
What Is the Blood Marker That Could Detect CTE?
The biomarker identified by researchers is known as eMTBR-tau243, a fragment of the tau protein.
Tau is a protein that normally helps maintain the internal structure of nerve cells. In certain neurodegenerative diseases, abnormal tau proteins accumulate and form toxic clumps in the brain. These accumulations are associated with conditions such as Alzheimer’s disease and CTE.
Researchers at Washington University had previously studied eMTBR-tau243 as a blood marker for Alzheimer’s disease. Their earlier work showed that levels of the protein fragment could reflect the accumulation of tau in the brains of people with Alzheimer’s.
The new research explored whether the same biomarker could provide information about other neurological conditions involving abnormal tau accumulation.
The researchers discovered that eMTBR-tau243 was also elevated in people with advanced CTE. This finding suggests that the biomarker may have applications beyond Alzheimer’s research and could eventually help scientists investigate other forms of tau-related brain disease.
How Researchers Discovered the Link Between Tau and CTE
The research was led by Kanta Horie and Chihiro Sato at Washington University School of Medicine, in collaboration with researchers at the University of California, San Francisco.
The team initially examined samples from more than 80 people with different brain diseases confirmed through autopsy, alongside healthy volunteers. During the analysis, researchers noticed an unusual result in one individual.
The person had elevated eMTBR-tau243 levels despite having no signs of Alzheimer’s disease in the brain. When researchers reviewed the individual’s autopsy records, they discovered evidence of advanced CTE.
This unexpected finding prompted the team to investigate whether the biomarker was associated with CTE more broadly.
Researchers subsequently examined blood samples from 11 people whose CTE diagnoses had been confirmed through autopsy. They found that eMTBR-tau243 levels were higher in these individuals than in healthy people. The levels also increased with the severity of the disease.
The overall study included 229 participants drawn from several research biorepositories. The findings provided preliminary evidence that the biomarker could reflect advanced CTE-related tau accumulation.
What Is Chronic Traumatic Encephalopathy?
Chronic traumatic encephalopathy is a progressive neurodegenerative disease associated with repeated blows to the head. It has attracted considerable attention because of its connection with contact sports and activities involving repeated head impacts.
People who may face increased exposure include:
- American football players.
- Boxers and other combat-sport athletes.
- Rugby players.
- Military personnel exposed to repeated head injuries.
- Others who experience repeated traumatic impacts to the head.
CTE is associated with abnormal accumulation of tau protein in particular regions of the brain. Over time, these changes can contribute to neurological problems.
Potential symptoms include memory difficulties, changes in behaviour, mood disturbances and problems with thinking. However, these symptoms can overlap with those of other neurological and psychiatric conditions, making diagnosis difficult.
At present, CTE can only be definitively confirmed through a postmortem examination of brain tissue. Doctors can evaluate symptoms and medical history while a person is alive, but these assessments cannot establish a definitive CTE diagnosis.
A reliable blood biomarker could help researchers move toward identifying the disease during a person’s lifetime.
Can the Blood Test Reliably Identify CTE?
The study produced encouraging results for advanced CTE, but it also identified important limitations.
Researchers found that eMTBR-tau243 could distinguish people with advanced CTE from healthy individuals with high accuracy. However, the biomarker did not reliably identify early-stage CTE.
Another challenge is that the same protein fragment is elevated in Alzheimer’s disease. Both conditions involve abnormal accumulation of tau, meaning the biomarker cannot independently establish whether a person has CTE or Alzheimer’s.
Researchers therefore do not consider eMTBR-tau243 a standalone diagnostic test for CTE.
| Research finding | What it means |
|---|---|
| Elevated eMTBR-tau243 in advanced CTE | Potential indicator of disease-related tau accumulation |
| Higher levels in 11 autopsy-confirmed CTE cases | Preliminary evidence supporting the association |
| Levels increased with disease severity | Possible usefulness in monitoring disease progression |
| Limited ability to detect early-stage CTE | More research is needed for early diagnosis |
| Also elevated in Alzheimer’s disease | Cannot independently distinguish the two conditions |
The researchers believe the biomarker may eventually become useful alongside a person’s medical history, symptoms and other diagnostic assessments.
For example, a person with a history of repeated head injuries and no evidence of Alzheimer’s could potentially undergo further investigation if the biomarker were elevated. However, this is a possible future application, not an established clinical procedure.
Why the Discovery Matters for Athletes and Military Veterans
A reliable way to identify CTE in living people could have important implications for athletes, military veterans and others exposed to repeated head impacts.
One major challenge in CTE research has been the inability to confirm the disease while patients are alive. This limits doctors’ ability to study how the condition develops and makes it difficult to evaluate potential treatments.
A validated blood biomarker could help researchers identify suitable participants for clinical trials. It could also provide a way to monitor changes in disease-related proteins over time.
The discovery may be particularly relevant as pharmaceutical companies investigate treatments targeting abnormal tau accumulation. Researchers need reliable biomarkers to determine whether experimental treatments are affecting the biological processes associated with a disease.
However, the current findings do not establish that the test can predict who will develop CTE or determine whether a person with a history of head injuries will eventually experience neurological problems.
Is the CTE Blood Test Available to the Public?
No. The biomarker has not yet been validated for diagnosing CTE in clinical practice.
Washington University has licensed the technology used to measure eMTBR-tau243 in blood to C2N Diagnostics, a university startup that has also developed a blood test to help diagnose Alzheimer’s disease.
The company and researchers may be able to use the technology in future studies, but the CTE application requires additional validation.
Larger studies will need to establish how accurately the biomarker identifies CTE across different stages of the disease and how well it distinguishes CTE from other neurological conditions involving abnormal tau.
Until that evidence is available, the research should be considered an important scientific lead rather than a ready-to-use diagnostic breakthrough.
The Bigger Picture
The discovery highlights the growing role of blood-based biomarkers in neurological research. Scientists have been working to identify measurable biological signals that could help detect brain diseases without relying exclusively on expensive imaging procedures or postmortem examinations.
For CTE research, the potential value is particularly significant because the condition has been difficult to study in living patients. A reliable biomarker could help researchers understand disease progression, identify participants for treatment trials and evaluate whether experimental therapies are working.
However, the overlap between CTE and Alzheimer’s disease demonstrates why a single biomarker may not be enough. Future diagnostic approaches could require multiple biological indicators combined with medical history and clinical assessments.
Looking Ahead
The next stage of research will involve larger studies to determine whether eMTBR-tau243 can reliably identify CTE in living people. Scientists will also need to establish whether combining the biomarker with other tests can improve diagnostic accuracy, particularly for early-stage disease. Until those studies are completed, the test cannot be considered a validated clinical diagnostic tool for CTE.
If the findings are confirmed, the discovery could change how researchers investigate a disease that has traditionally been diagnosed only after death. It may also support future clinical trials targeting abnormal tau accumulation, offering a potential route toward better diagnosis and treatment research for people affected by repeated head injuries.
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