A novel blood test measuring glial fibrillary acidic protein levels may help distinguish between hemorrhagic and ischemic strokes before patients reach the hospital, according to preliminary research presented at the American Stroke Association's International Stroke Conference 2025.

In the study, investigators found that glial fibrillary acidic protein (GFAP) levels were nearly 7 times higher in patients who had bleeding strokes compared with those who had clot-caused strokes (208 pg/mL vs 30 pg/mL). This distinction could potentially accelerate appropriate treatment delivery, as hemorrhagic and ischemic strokes require opposing therapeutic approaches, according to a press release from the American Heart Association.

"It is crucial to differentiate these two types of strokes because they need opposite treatments. In ischemic stroke, you need to open the blocked blood vessel with clot-busting drugs or physically remove the clot. In contrast, in a bleeding stroke, you need to lower increased blood pressure and give medication to reverse the effects of certain blood-thinning drugs," said lead study author Love-Preet Kalra, MD, a neurology resident at the RKH Hospital Klinikum Ludwigsburg in Germany, in a statement.

The investigators evaluated 353 patients (average age = 75, 47% women) who arrived at the emergency room within 6 hours of stroke symptom onset. Using age-based cut-off points, the test demonstrated 90% to 95% accuracy in predicting bleeding strokes.

"I was personally surprised by the extremely elevated GFAP values in blood thinner–associated bleeding stroke and the fact that, in [patients with] moderately or severely affected acute stroke, bleeding stroke could be excluded in all cases [that] showed a GFAP lower than 30 pg/mL," Dr. Kalra noted.

The test showed particular utility in several key areas:

• GFAP levels were more than 4 times higher in patients with bleeding stroke compared with stroke mimics.
• The test could rule out bleeding stroke when levels fell below 30 pg/mL in patients with moderate to severe neurological deficits.
• Higher GFAP levels were observed in patients with bleeding stroke taking blood thinners.

However, the investigators noted limitations in the abstract, including the need for blood centrifugation and potential challenges in identifying small bleeding strokes in elderly patients as a result of age-related GFAP increases.

If validated by larger studies, this diagnostic approach could revolutionize prehospital stroke care.

"Treatment to lower blood pressure and reverse blood-thinning medications could be performed in the prehospital setting, leading to a huge change in clinical practice. In the future, even blood thinners or clot-busting treatment might be applied before [patients] reach the hospital," Dr. Kalra concluded.

The study excluded patients with previous brain tumors or recent stroke/traumatic brain injury. Blood samples were collected and analyzed using a portable blood analyzer before emergency room arrival at the RKH Hospital Ludwigsburg.