A new blood test could help doctors tell the difference between a bleeding stroke and a clot-caused stroke before a patient even reaches the hospital.
This finding comes from a preliminary study to be presented at the American Stroke Association’s International Stroke Conference 2025 in Los Angeles.
When someone has a stroke, every minute counts. The longer the brain goes without the right treatment, the more damage occurs, and the greater the risk of permanent disability or death.
But before treatment can begin, doctors must know whether the stroke is ischemic (caused by a blood clot) or hemorrhagic (caused by bleeding in the brain), because each requires a completely different approach.
Clot-caused strokes need drugs or procedures to remove the blockage, while bleeding strokes require lowering blood pressure and reversing the effects of any blood thinners. Currently, doctors confirm the type of stroke using brain scans, but getting to that step can take hours.
In this study, researchers investigated whether a blood protein called glial fibrillary acidic protein (GFAP) could provide a faster answer.
GFAP is released into the blood when brain cells are damaged, and previous research has shown it can help detect brain injuries. The team collected blood samples from patients in an ambulance before they arrived at the emergency room.
The results were promising. GFAP levels were almost seven times higher in people with bleeding strokes compared to those with clot-caused strokes, and more than four times higher than in people whose symptoms mimicked a stroke.
The study also found that a GFAP level below 30 picograms per milliliter could reliably rule out a bleeding stroke in patients with moderate to severe symptoms. Using age-based cut-off points, the test could predict a bleeding stroke with 90%–95% accuracy.
Interestingly, bleeding stroke patients taking blood thinners had even higher GFAP levels than those not on these medications.
The study included 353 people (average age 75, 47% women) who arrived at the hospital within six hours of their first symptoms. Of these, 76 had bleeding strokes, 258 had clot-caused strokes, and 19 had other conditions such as seizures or migraines.
If confirmed in larger studies, this blood test could allow paramedics to start treatment—such as lowering blood pressure or reversing blood thinners—before the patient reaches the hospital. In the future, even clot-busting drugs might be given en route.
However, there are limitations: the current version of the test requires a centrifuge, and GFAP levels tend to rise with age, which could make diagnosing small bleeding strokes harder in older patients.
Experts say that while the study is small, it shows strong potential for improving prehospital stroke care. A rapid “point-of-care” GFAP test in ambulances could revolutionize stroke treatment by saving precious time and brain tissue.
If you care about stroke, please read research about Stronger high blood pressure treatment may help prevent stroke in older people and findings of Stroke death risk increases again after falling for 40 years.
For more about stroke, please read research about Research finds a better high blood pressure treatment for stroke patients and findings of Scientists find a better drug than statins for stroke patients.
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