The Glasgow Coma Scale is a clinical scale used to reliably measure a person's level of consciousness after a brain injury. The GCS assesses a person based on their ability to perform eye movements, speak, and move their body. The highest possible score is 15 and the lowest possible score is 3. A score of 15 indicates a best response (fully conscious patient), score of 8 or less indicates a comatose patient and a score of less than 3 indicates complete unresponsiveness. The above picture shows the glasgow coma scale and its values.