Methods and apparatus for determining blood brain barrier (BBB) damage and treating patients who may have suffered from BBB damage due to an ischemic event are provided. The methods and apparatus involve detecting the presence of cleaved occludin fragments in a sample of blood. According to some embodiments, the method further provides determining the degree of BBB damage based on the concentration of occludin fragments in the sample. In further embodiments the present disclosure provides kits for detecting the presence of occludin fragments in a blood sample.