PITTSBURGH — More than a month after sustaining a concussion, Luke Kusler was having trouble focusing in class, getting irritated easily, and feeling his body veer to one side when he walked down crowded school hallways.

The 13-year-old right tackle was sidelined by a big shot early in the season and doctors looking at his results on a post-concussion test were wondering if those crushing hits might have ended his playing days.

Even so, the 6-foot, 200-pound eighth-grader was itching to get back into the game.

“I’m a lineman,” he said. “That’s what we do.”

Luke’s doctor had given him the ImPACT test, which has gained wide use in the U.S. as awareness about concussions and their long-term effects has risen in recent years. Doctors say ImPACT and other neurocognitive exams have transformed the way concussions are managed by giving a tangible measure of what’s going on in the brain — and proof for eager athletes that their heads may not be ready to take the next hit.

“There will always be concussions. The key is trying to prevent long-term injuries,” said Dr. Mark Lovell, a founding director of the University of Pittsburgh Medical Center Sports Medicine Concussion Program and ImPACT’s co-creator.

ImPACT, which stands for Immediate Post-Concussion Assessment and Cognitive Testing, is a 20-minute, computer-based series of fast-paced quizzes involving words, pictures and colors. Scores reflect how quickly and correctly the questions are answered, and are compared to a baseline test that athletes take at the beginning of a season.

“Think of it as a stress test for the brain,” Lovell said. “It tells us something about what’s going on for that individual and it makes it very hard to hide their symptoms.”

The test was developed in the early 1990s by Lovell and Dr. Joseph Maroon, the longtime neurosurgeon for the Pittsburgh Steelers. Maroon was irritated when then coach Chuck Noll asked him what proof he had to keep an injured player out of the game.

“He challenged everything and I was really upset by that,” Maroon said. “He was right. Where was my proof?”

The Steelers began baseline testing of all their players using ImPACT in 1997. The practice was later adopted by the NFL for all players in 2001, and the NHL, MLB and other professional leagues followed suit.

The tests are now given to more than 4 million college, high school and youth athletes in the U.S. High schools pay $500 to $700 per year to use ImPACT; pro teams pay about $1,000 a year.

Doctors say the tests shouldn’t be the only factor a doctor or athletic trainer considers when making return-to-play decisions. The patient’s medical history, strength, coordination and balance also need to be weighed.

The tests also can be influenced if the athlete is fatigued or distracted, or is motivated to get back in the game, said Dr. Jeffery S. Kutcher, the director of Michigan NeuroSport and a member of the American Academy of Neurology.

“These programs are really an extension of our physical examination and they should never be used to diagnose concussion or make a return-to-play decision without seeing a physician,” the neurologist said.

A concussion occurs when the brain is shaken, causing a cellular disruption that can’t be detected on a brain scan or X-ray. Symptoms, which often aren’t present for a day or two after a hit, can include headaches and memory and coordination problems.

In the past, athletes who suffered a hit to the head might have been sidelined for the rest of the game or put back in after sitting out a play or two to “shake it off,” Lovell and Maroon said. Doctors now understand that there may be catastrophic consequences if a person has repeated concussions before getting a chance to heal. And the only way to do that is through physical and mental rest.

Although 300,000 sports-related concussions are diagnosed every year in the U.S., the American College of Sports Medicine estimates that about 85 percent go undetected, putting the athletes at risk of suffering even more severe injuries.

And no two brains react the same to a hit, so there isn’t a one-size-fits-all treatment.

At UPMC’s Sports Medicine Concussion Program, Lovell and other doctors see about 10,000 patients a year.

One of them was 13-year-old Logan Stork, who was hit from behind and forced into the boards face first during a hockey tournament a few days earlier.

“All I remember is going down on the ice and getting taken off the ice on a stretcher,” Logan said. He spent five hours in the hospital, and then watched from the bench.

Logan had suffered a concussion before, so his parents wanted to take every precaution. Fortunately, Lovell said that Logan’s good ImPACT score and his complaints of a stiff neck probably indicated a neck strain and not a concussion.

“The bottom line is we don’t want anyone to go back while they are still having symptoms,” Lovell said.

In the room across the hall, Lovell was seeing Luke Kusler for his follow-up visit. Luke’s ImPACT scores were higher than a month ago, but still not back to normal. The teen also had trouble balancing when Lovell had him stand on a foamlike square in the exam room with one leg up and his eyes closed.

Even so, Luke wants to get back in the game — any game — and asked when he could start conditioning for baseball.

Lovell cautioned the teen that he wasn’t ready.

“If we treat this well, you are going to be able to play again,” Lovell said. “If we rush you back too soon, that’s when the real trouble starts.”