It wasn't so long ago that shaking off a knock to the head and getting back on the field was seen as a sign of toughness for sportspeople. But in recent years, increased awareness of the potential for long-term damage has put the seriousness of concussion in the spotlight. Researchers at Sahlgrenska Academy in Sweden have now developed a blood test that reveals the severity of a concussion and when it is safe for a player to return to the game.

Diagnosing the severity of concussion is notoriously difficult, with many concussions not producing any noticeable signs or symptoms. Neuropsychological tests are one of the most common diagnostic tests used by sporting team medical staff to ascertain whether a person is concussed, but researchers from Sahlgrenska Academy at the University of Gothenburg wanted to find a more definitive diagnostic test.

To this end, the researchers monitored and examined all the players in Sweden's top hockey league. Ice hockey is a notoriously violent sport, with 35 of the 288 players in the Swedish Hockey League sustaining a concussion just half way into the 2013 season. These 35 players were asked to provide blood samples directly after and during the days after they received a concussion. These samples were then compared to samples taken from two full teams before the season began.

The tests showed that concussed players had elevated levels of a special nerve protein, called tau, in the blood. By measuring the levels of tau in a standard blood test, the researchers say it is possible to determine the severity of a concussion one hour after the injury was sustained. Additionally, the test can predict with an even greater degree of accuracy which players would experience long-term symptoms and therefore need to rest for longer.

"In contact sports like ice hockey, boxing and American football, concussions are a growing international problem," says Henrik Zetterberg, Professor at the Institution for Neuroscience and Physiology, the Sahlgrenska Academy. "The stakes for the individual athlete are high, and the list of players forced to quit with life-long injury is getting ever longer.

"We hope that this method will be developed into a clinical tool for club physicians and others in sports medicine, and is used as a basis for the decision on how long the player should rest after a blow to the head. It could even be used in general in emergency medical care to diagnose brain damage from concussions regardless of how they happened."

Results of the study, which was conducted in collaboration with researchers at Luleå University of Technology, Sahlgrenska University Hospital and the US biotech firm Quanterix Corporation, appear in the journal JAMA Neurology.