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Having a concussion may not be the only indicator of brain damage among football players.

A recent study from the Cleveland Clinic and the University of Rochester reports that football players may experience long-term brain changes even if they haven’t suffered a concussion. The researchers studied 67 college football players and after each game, conducted brain scans and blood tests, to determine the extent of brain injury. In the blood, the researchers searched for S100B, a protein that is involved in regulating nerve growth that has been associated with certain neurological conditions such as Alzheimer’s disease, epilepsy, amyotrophic lateral sclerosis (ALS) as well as certain cancers. They found that the more hits the players received to the head, the higher the level of S100B that seeps into the blood stream after an injury.

(MORE: Study Details How Brain Injury from Concussions Progresses)

None of these hits were classified as a concussion, but four players showed symptoms of an autoimmune response that is linked to brain problems like epilepsy and dementia.

HealthDay writes:

If this protein is repeatedly released into the bloodstream, the body’s immune system will eventually take notice of the protein. And, because it’s a protein not normally seen in the blood, the immune system may see it as a foreign invader, much like bacteria or viruses. If the immune system feels it’s a dangerous foreign substance, it will create antibodies against the protein, presumably to destroy it, which is what these researchers found.

Diagnosing brain injury in high-impact sports players is receiving more attention in recent months given the growing body of research documenting the high prevalence of memory loss among NFL players. Concussions are difficult to diagnose since they rely heavily on the player’s symptoms and pricey brain scans. The sports culture also discourages players from reporting their symptoms out of pride and the desire to keep playing and not watch from the sidelines.

But the dangers of head injuries, and their potentially long-lasting effects, are prompting more doctors and players, not just in the NFL but in other sports as well, to take the risk seriously. In November, a study found that soccer players, who head oncoming balls directly, have changes in the protective white matter in their brains, even if they haven’t suffered from concussions.

MORE: NFL Players May Be More Vulnerable to Alzheimer’s Disease

The report on the football players, published in the journal PLOS ONE, suggests that blood tests could be an inexpensive and objective way to predict or measure brain trauma. According to the study authors, the test would cost around $40 and could easily be performed at stadiums.

Preventing concussions from happening, and minimizing their effects when they do, is another way to reduce the toll that direct contact sports can have on athletes. Other research suggests that players may protect themselves from concussions by strengthening neck muscles to avoid the extreme jarring motion that can rattle the brain and cause damage to delicate tissues. Presenting their findings at the fourth annual Youth Sports Safety Summit in early February, researchers said that the stronger the neck, the lower the risk of suffering a concussion.

TIME reported:

This new study is very promising. Neck strengthening exercises are easy. For example, you can use your own hands as a resistance tool — put your hands on the back of your head, and press them forward while your bend your neck backwards. They don’t require any huge investment in additional equipment; that’s important for today’s cash-strapped schools.

More research is needed to determine the best way to assess brain damage and even diagnose concussions, but the researchers believe that as such studies continue, athletes may be able to take advantage of more systems that can protect and detect potential brain injury early.