– For decades, researchers have been seeking a blood test that could diagnose a concussion and tell whether it is severe enough to cause lasting brain damage.

In a big step toward that goal, University of Pennsylvania scientists found that a blood protein called SNTF surged and stayed elevated in professional hockey players with persistent concussion symptoms, but not in players who recovered within a few days.

“These results show that SNTF has promise as a blood biomarker for sports-related concussion,” said Robert Siman, a professor of neurosurgery at Penn and lead author of the study in last month’s Journal of Neurotrauma.

Every year, a million people in the U.S. — many of them young athletes — are hit on the head, causing the mild brain trauma known as concussion. Although most recover within hours or days, a minority suffer lasting symptoms of brain injury such as headaches, confusion and irritability.

Current diagnostic tests for concussion are imprecise and indirect; even a CT scan may show nothing unusual. Test results often leave coaches and athletes unsure about whether returning to play is safe — or liable to lead to disabling, potentially fatal, reinjury.

Siman and his Penn team discovered SNTF and have spent 20 years studying it, hoping to find a blood protein that correlates with brain injury the way troponin signals cardiac damage. SNTF is normally undetectable in brain nerve cells called axons. But after injury, the protein accumulates in axons and spills into the blood — even when a CT scan seems normal.

In a past study of concussion treated in the emergency room, Siman’s team found that patients who had brain abnormalities on MRI scans or thinking problems that persisted at least three months had elevated SNTF blood levels. The new study, done with Swedish researchers, used blood drawn before and during the hockey season from 73 Swedish professional hockey players, including 28 who had concussions. By measuring SNTF after a training session, the study also found that exertion did not affect the level.

“Contact sports are being played differently now. Athletes get hit a lot more,” Bazarian said. “A protein like this (SNTF) is so desperately needed. We need a way to pull athletes out of a game, prick their finger, and not even ask them their symptoms. We need to take the guesswork out of diagnosing concussion.”

Though SNTF needs to be validated in a larger, longer study, Siman said he was pursuing development of a commercial test. A reliable test could open the door to developing something else that is desperately needed — a way to heal concussion.