The Sunday after Thanksgiving last year proved tragic for family and friends of 22-year-old Kosta Karageorge. The defensive tackle for the Ohio State Buckeyes was found dead that day after apparently shooting himself in the head. Looking for a cause for this terrible event, his family noted that he had suffered several recent concussions, which had left him confused, disoriented and emotional.

No one knows whether concussions played a role in Karageorge’s suicidal behavior. But head injuries can spawn neurodegenerative changes that could lead athletes down that road. Other suicides, such as that of high school hockey player Willy Alexander Thomas, who jumped off the George Washington Bridge in October of 2013, were also preceded by at least one concussion.

A blow to the head does not generally lead to suicide, and often produces no serious problems. In fact, 80 to 90 percent of those who suffer from mild traumatic brain injury (TBI)—head trauma in which a loss of consciousness or cognitive changes last less than half an hour—will recover fully. Yet right now there is no way to tell early on which people with mild TBI will not be fine, even months or years later.

Neuroscientist Robert Siman at the University of Pennsylvania and his colleagues have taken an important step toward solving some of this mystery. They have found a protein fragment in the blood whose levels parallel how badly the brain is damaged. A blood test for this fragment could thus reveal how soon it is safe for a concussion victim to resume normal activities—including sports. It might also open the door to finding out which therapies for brain injury actually work.

About 12 years ago Siman and his colleagues decided to look for proteins in blood that could serve as markers for brain damage. A protein fragment called SNTF was a good candidate. SNTF is part of a structural protein called spectrin in neurons. When neurons are stretched and deformed, chemical changes activate an enzyme that cuts spectrin, creating SNTF and causing it to accumulate in the cell. In serious cases, the fragment spills out of cells and enters the blood.

To test whether SNTF levels in the blood might be a good marker for neuronal injury, Siman and his team followed 288 players in the top professional hockey league in Sweden for half of the 2012-2013 season. Of the 28 players who got concussions during this time, 20 had symptoms that lasted for six days or more. One player’s symptoms persisted for so long that he decided to retire. In those players with lasting injuries, blood levels of SNTF were much higher one hour to six days later than were SNTF levels in the eight athletes whose concussions cleared up within five days. Levels were also low in 45 players who did not have concussions and were tested during the preseason. A blood test for SNTF might thus forecast recovery time from a head injury. Players and others with mild traumatic brain injuries who have elevated levels in the ER are more likely to have cognitive problems that persist. (For more on this study, listen to the 60-Second Mind podcast, “Blood Test Forecasts Concussion Severity.”)

Additional testing could also help determine whether an athlete has recovered enough to play again. Currently, decisions about putting an athlete back on the court, field or ice are based on the disappearance of symptoms such as dizziness, nausea, headaches, confusion and disorientation. When all such symptoms are gone, exercising and then game play are gradually reintroduced. But because evaluating symptoms is subjective, blood test results could provide important additional information. “An objective, quantitative test tied to brain functions could have a lot of utility in return to play decisions,” Siman says. The blood test could be similarly useful, he adds, in determining when a victim of a fall, motor vehicle collision or other accident can safely return to school or work.

The Penn team’s simple assay also could be a boon for evaluating possible brain injury treatments. To date, no therapy for brain injury has any real scientific backing. No one even knows for sure whether the common practice of resting the brain speeds recovery—or, if it does, what the components or duration of the rest should be. Evaluating remedies on all brain injury patients is difficult to impossible because so many get better on their own. But identifying those patients whose injuries will persist could provide a practical patient population on which to test therapies.

Potentially an SNTF blood test might even be useful in detecting those players at risk for chronic, long-term neurological problems. SNTF is not detectable in the blood of healthy individuals, but the researchers did find low levels in 42 percent of the hockey players tested during the preseason. Although the meaning of this finding is not clear, one possibility is that chronic elevation of this molecule may be common in people who participate in contact sports at a high level—and could put them at risk for a neurodegenerative disease such as chronic traumatic encephalopathy. Such a blood marker would be quite useful in determining how much monitoring, care and attention a person needs—especially if the early stages of degenerative disease put him or her at risk for suicide.