There is not a definitive test that can diagnose a concussion like a blood test or imaging scan. A concussion is usually diagnosed based on physical symptoms, cognitive impairment, and neurological examination. A healthcare professional might assess the person's balance, coordination, reflexes, and memory. In cases with severe symptoms or those that don't improve over time, a CT scan or MRI may be ordered, primarily to rule out more serious brain injuries, such as bleeding or swelling in the brain. However, most concussions won't show up on these types of scans.