Provided is a method for detecting injury to the brain comprising: a) determining the level of a tight junction (TJ) protein in exosomes isolated from a test sample from a subject, wherein the TJ protein is occludin, claudin-3, claudin-5, claudin-12, ZO-1, ZO-2, ZO-3, JAM-A, JAM-B or JAM-C, or any combination thereof b) comparing the level of the TJ protein in the test sample to the level of the TJ protein in a control sample, wherein an elevated level of the TJ protein in the test sample relative to the level of the TJ protein in the control sample indicates that the subject has an injury to the brain.
