In the movie “Concussion,” which is based on the life of Bennet Omalu, a doctor who studied traumatic brain injury, Omalu explains that the reason the prognosis is so poor for so many of them is because their symptoms went undiagnosed.

When head injuries aren’t treated or are undertreated, patients are at risk of more-serious injury. This is why children with concussions are often asked not to return to class or sports until their symptoms have resolved and adults often have to take days off work.

One of the challenges has been that concussions are tricky to diagnose, and it isn’t uncommon for a patient to rush to the emergency room, only to be met with a vague response from the doctor about whether there’s anything worrisome. Symptoms often aren’t apparent for hours or even days after the initial injury, and the imaging technology we have can’t pick up anything other than larger bleeds and lesions.

How different could things have been if there was a simple blood test to detect a concussion?

In a paper published in JAMA Neurology on Monday, researchers reported that they may be closer than ever to such a test. The study involved 600 patients admitted to a trauma center from March 2010 to March 2014. All had suffered some kind of head injury resulting in loss of consciousness, amnesia or disorientation.

The researchers drew the participants’ blood when they were initially admitted and at regular intervals in the days following to look at how a level of a biomarker known as glial fibrillary acidic protein (GFAP) changed over time.

The blood samples showed that GFAP peaked at 20 hours after injury and slowly declined over 72 hours but continued to be detectable for seven days.

The researchers wrote that the marker “performed consistently” in helping detect mild to moderate traumatic brain injury and traumatic intracranial lesions. This could help diagnose not only patients in ERs but also those who never made it there but may find that they have symptoms such as confusion or headache days later.

GFAP is unique to the brain and central nervous system and has been shown in previous research to play a critical role in repairing the body. After a head injury, it is released into the bloodstream.

“We have so many diagnostic blood tests for different parts of the body, like the heart, liver and kidneys, but there’s never been a reliable blood test to identify trauma in the brain,” lead author Linda Papa, an emergency medicine physician at Orlando Health, said in a statement. “We think this particular test could change that.”

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