There are three grades of concussions. Loosely speaking, determining which grade to assign a concussion depends on the duration of the loss of consciousness. The three primary systems used today were developed by Cantu, Colorado Medical Society, and American Academy of Neurology [source: Lew].
Using the Cantu scale, a concussion is categorized as grade one (mild) if there has been no loss of consciousness, and posttraumatic amnesia lasts for less than 30 minutes after the injury. If loss of consciousness occurs, but it last for less than five minutes, and posttraumatic amnesia lasts for more than half an hour, then Cantu classifies the injury as a grade-two (moderate) concussion. Finally, if the victim loses consciousness for more than five minutes, and posttraumatic amnesia persists for more than 24 hours, then the concussion is considered grade three (severe) [source: Lew].
The Colorado scale is simpler, and it says that a concussion that results in no loss of consciousness, no confusion and no amnesia should be classified as grade one. A concussion that results in no loss of consciousness, but some confusion and amnesia should be considered grade two. And a concussion that results in any loss of consciousness at all should be treated as a grade-three concussion [source: Lew].
The American Academy of Neurology's system is very similar to that of the Colorado Medical Society's. According to the AAN, a victim of a grade-one concussion may experience some transient confusion, but the concussion symptoms will resolve in less than 15 minutes, and no loss of consciousness will occur. A grade-two concussion is exactly the same, except the symptoms last for more than 15 minutes. A grade-three concussion, according to the AAN, is any that results in loss of consciousness, whether it lasts only a few seconds or several minutes [source: Lew].
There are cognitive tests for determining whether someone is experiencing concussion symptoms, and many of them provide their own "return to play" guidelines. AAN maintains that someone who has had a grade-one concussion may resume physical activity after 15 minutes of exhibiting no post-concussion symptoms. If someone has had a grade-two concussion, the victim can return to play after being symptom-free for one to two weeks and with clearance by a physician. But grade-three concussions require hospitalization, and the athletes must be asymptomatic for at least two to four weeks with a physician's clearance before returning to play [source: Lew].