A new blood test can tell doctors whether a person has suffered a concussion up to a week after he or she was injured. A study describing the test was published in the journal JAMA Neurology. People who suffer a head injury should rest soon after they are hurt. Doctors say rest is important in helping the brain to heal after the injury. Individuals who have suffered a concussion do not always show symptoms. Experts say those warning signs can be delayed, especially in children. A concussion can lead to a feeling of dizziness, headaches and an inability to sleep. These problems can exist for a long time. Some concussion patients have experienced loss of memory, trouble thinking and feelings of anxiety. Doctors at Orlando Health System in Florida developed the new blood test. It shows if a biomarker is present in a person’s blood.