Concussions can be tricky to diagnose. Making it even harder, sometimes people brush off a head injury at first and only days later decide to see a doctor.

But soon physicians may have a new tool to help. A study by researchers from Orlando Regional Medical Center shows that a simple blood test can detect whether or not someone has suffered a concussion as long as a week after the initial injury. The test may even eventually help guide treatment in individuals.

The study included 584 patients with trauma-related injuries who visited Orlando Regional Medical Center, a Level 1 Trauma Center. Half had brain-related injuries and half had other types of traumatic injuries, such as broken bones.

The scientists ran blood tests on the study participants at their initial visits, looking for two biomarkers, called GFAP and UCH-L1, which are released into the bloodstream after a head injury. Biomarkers are molecules that can be measured to help doctors detect changes in the body related to injury and disease.

Get Breaking News Delivered to Your Inbox

The blood tests were repeated every four hours for the first 24 hours and then twice a day for the next six days, study author Dr. Linda Papa, an emergency physician and director of clinical research at Orlando Regional Medical Center, told CBS News.

"In all, we had twenty time points -- twenty blood draws over the course of the seven days," said Papa.

The biomarker GFAP, short for glial fibrillary acidic protein, peaked at 20 hours but "was working consistently over the seven days," she said. UCH-L1 peaked more quickly, within eight hours.

The study, published today in JAMA Neurology, showed that the diagnostic accuracy of GFAP exceeded that of UCH-L1, helping to distinguish patients with mild traumatic brain injury from the study's control group patients within seven days after injury.

The study showed that patients who exhibited traumatic brain injury symptoms on CT scans had higher levels of the two biomarkers, too, especially GFAP.

What's more, the authors said GFAP appears to "predict neurosurgical intervention consistently over seven days after injury, whereas the ability of UCH-L1 seems to be more limited to the earliest time points after injury."

Knowing who has a more serious injury based on the blood test could help limit the number of unnecessary brain scans, said Papa.

A biomarker blood test could also be very useful in people who don't seek medical treatment immediately but show up in the emergency room or the doctor's office days later with possible concussion symptoms, including dizziness, headache, memory problems, fatigue, and feeling dazed.

"About 20 percent of people who have concussions don't come in right away," Papa said, explaining that the typical delayed visit includes someone who's been playing recreational sports, such as flag football or soccer, or who's been injured while drinking alcohol and only later realizes they still feel unwell.

The findings have implications for developing future concussion studies and therapies, she noted.

"A patient may have symptoms of a concussion and may want to participate in a [therapy] trial. The blood test shows if indeed the biomarkers are elevated, and if so, we could put them in a study," said Papa.

"Having a good marker that determines if there's an injury can help guide us on which therapies will work and which will not."