Methods and kits useful in the detection of occult blood in biological samples and specimens, for example to screen for colorectal cancer or detect blood in samples ex vivo, e.g., at a crime scene. Also provided are methods useful in diagnosing whether a subject is predisposed to, or suffers from, an occult-blood related disorder; and methods for direct micro-mapping of the distribution of occluded vessels associated with cerebral vascular injury.