Concussions are a growing problem in competitive sports and doctors may soon have a blood test that will detect the injury's extent and later help determine when an athlete is fit to play.

The test has emerged from Sahlgrenska University Hospital in Sweden and targets the brain protein tau, which long has been under study for its role in Alzheimer's disease.

Dr. Pashtun Shahim, who studied injured Swedish ice hockey players, found they sustained high levels of the protein, which is produced by the central nervous system.

The protein can be detected in the blood, Shahim and his colleagues found, and they have alerted the global medical community to a new way to screen for traumatic brain injury. Shahim and his team reported their discovery in Thursday's JAMA Neurology.

"We have been trying to do something like this in Alzheimer's disease for 30 years and have not yet succeeded," said Dr. Samuel Gandy, who chairs Alzheimer's research at The Mount Sinai School of Medicine in Manhattan.

"This is an extremely interesting and groundbreaking paper," he said.

Two years ago, Gandy suggested screening young athletes for the Alzheimer's-related gene, APOE-4, because carriers are more likely to develop the disease in old age as a result of traumatic brain injury sustained in youth.

He sees possibilities for more accurate diagnoses because of the Swedish research.

"This looks extremely promising for quantifying and measuring the effect head injury has on a brain protein that appears in the blood," he said. "It could be useful for diagnosis and prognosis."

Gandy is an expert in the brain condition dementia pugilistica, once believed to occur only in boxers. Now, the condition is called chronic traumatic encephalopathy -- CTE -- and it is known to affect severely head-injured athletes in a variety of sports.

Dr. Philippe Marambaud, director of the Laboratory of Memory Disorders at the Feinstein Institute for Medical Research in Manhasset, said the protein tau has been under intense research at his institution for years.

Tau, Marambaud said, is one of the key biological culprits that destroys brain tissue in Alzheimer's disease. But scientists, he added, have long been aware of its presence in injured athletes.

"We knew that looking at the brain [tissue] from athletes who died that tau accumulated," Marambaud said. "So the new idea in this paper is that it is not only in the brain but in the plasma in the blood. You can look at tau in the blood now, which is extremely important."

The Centers for Disease Control has declared traumatic brain injury a serious problem, estimating about 1.7 million cases annually. Nearly three-quarters of them are concussions that have occurred as a result of accidents of all kinds.

Dr. Robert Glatter, director of sports medicine and traumatic brain injury at Lenox Hill Hospital in Manhattan, said he's pleased a new biomarker is on the horizon.

"We currently use measures such as balance-testing and rapid number naming with eye movements as ways to screen for concussions," Glatter said. "The addition of a valid biomarker, such a total tau to quantify whether a player truly has suffered a concussion, and to then track progress, based on its level in the bloodstream, represents a potential advance in providing optimal care," he said.

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